The potential existence of a giant planet orbiting within a few AU of a stellar remnant has profound implications for both the survival and possible regeneration of planets during post-main sequence stellar evolution. This paper reports Hubble Space Telescope Fine Guidance Sensor and U.S. Naval Observatory relative astrometry of GD 66, a white dwarf thought to harbor a giant planet between 2 and 3 AU based on stellar pulsation arrival times. Combined with existing infrared data, the precision measurements here rule out all stellar-mass and brown dwarf companions, implying that only a planet remains plausible, if orbital motion is indeed the cause of the variations in pulsation timing.
We present low-resolution MMT Hectospec spectroscopy of 594 candidate Monoceros stream member stars. Based on strong color-magnitude diagram overdensities, we targeted three fields within the stream's footprint, with 178 deg < l < 203 deg and -25 deg < b < 25 deg. By comparing the measured iron abundances with those expected from smooth Galactic components alone, we measure, for the first time, the spectroscopic metallicity distribution function for Monoceros. We find the stream to be chemically distinct from both the thick disk and halo, with [Fe/H] = -1, and do not detect a trend in the stream's metallicity with Galactic longitude. Passing from b = +25 deg to b = -25 deg the median Monoceros metallicity trends upward by 0.1 dex, though uncertainties in modeling sample contamination by the disk and halo make this a marginal detection. In each field, we find Monoceros to have an intrinsic [Fe/H] dispersion of 0.10-0.22 dex. From the CaII K line, we measure [Ca/Fe] for a subsample of metal poor program stars with -1.1 < [Fe/H] < -0.5. In two of three fields, we find calcium deficiencies qualitatively similar to previously reported [Ti/Fe] underabundances in Monoceros and the Sagittarius tidal stream. Further, using 90 spectra of thick disk stars in the Monoceros pointings with b ~ +/-25 deg, we detect a 0.22 dex north/south metallicity asymmetry coincident with known stellar density asymmetry at R_GC ~ 12 kpc and |Z| ~ 1.7 kpc. Our median Monoceros [Fe/H] = -1.0 and its relatively low dispersion naturally fit the expectation for an appropriately luminous M_V ~ -13 dwarf galaxy progenitor.
Optical-UV photometry of blazars detected by the Fermi satellite and classified as BL Lacs allowed to determine the redshift for a handful of objects and redshift upper limits for the great majority. A few of these are candidates to be "blue quasars", namely FSRQs whose broad emission lines are hidden by an overwhelming synchrotron emission peaking in the UV. This implies that the emitting electrons have high energies, which in turn requires relatively weak radiative cooling, a condition that can be met if the main radiative dissipation of the jet power occurs outside the broad line region. We confirm this hypothesis by studying and modelling their spectral energy distributions and argue that these objects are a minority within the blazar populations.
Every experiment is affected by systematic effects that hamper the data analysis and have the potential to ultimately degrade its performance. In the case of probes of the cosmic microwave background (CMB) radiation, a minimal set of issues to consider includes asymmetric beam functions, correlated noise, and incomplete sky coverage. Presuming a simplified scanning strategy that allows for an exact analytical treatment of the problem, we study the impact of systematic effects on the likelihood function of the CMB power spectrum. We use the Fisher matrix, a measure of the information content of a data set, for a quantitative comparison of different experimental configurations. In addition, for various power spectrum coefficients, we explore the functional form of the likelihood directly, and obtain the following results: The likelihood function can deviate systematically from a Gaussian distribution up to the highest multipole values considered in our analysis. Treated exactly, realistic levels of asymmetric beam functions and correlated noise do not by themselves decrease the information yield of CMB experiments nor do they induce noticeable coupling between multipoles. Masking large fractions of the sky, on the other hand, results in a considerably more complex correlation structure of the likelihood function. Combining adjacent power spectrum coefficients into bins can partially mitigate these problems.
The Wide-field Infrared Survey Explorer (WISE) is an extremely capable and efficient black hole finder. We present a simple mid-infrared color criterion, W1-W2 \geq 0.8 (i.e., [3.4]-[4.6] \geq 0.8, Vega), which identifies 61.9 \pm 5.4 AGN candidates per deg2 to a depth of W2 = 15.0. This implies a much larger census of luminous AGN than found by typical wide-area surveys, attributable to the fact that mid-infrared selection identifies both unobscured (type 1) and obscured (type 2) AGN. Optical and soft X-ray surveys alone are highly biased towards only unobscured AGN, while this simple WISE selection likely identifies even heavily obscured, Compton-thick AGN. Using deep, public data in the COSMOS field, we explore the properties of WISE-selected AGN candidates. At the mid-infrared depth considered, 160 uJy at 4.6 microns, this simple criterion identifies 78% of Spitzer mid-infrared AGN candidates according to the criteria of Stern et al. (2005) and the reliability is 95%. We explore the demographics, multiwavelength properties and redshift distribution of WISE-selected AGN candidates in the COSMOS field.
We investigate galactic-scale outflowing winds in 72 star-forming galaxies at z~1 in the Extended Groth Strip. Galaxies were selected from the DEEP2 survey and follow-up LRIS spectroscopy was obtained covering SiII, CIV, FeII, MgII, and MgI lines in the rest-frame ultraviolet. Using GALEX, HST, and Spitzer imaging, we examine galaxies on a per-object basis in order to understand both the prevalence of galactic winds at z~1 and the star-forming and structural properties of objects experiencing outflows. Gas velocities, measured from the centroids of FeII interstellar absorption lines, span the interval [-217, +155] km/s. We find that ~40% (10%) of the sample exhibits blueshifted FeII lines at the 1-sigma (3-sigma) level. We also measure maximal outflow velocities using the profiles of the FeII and MgII lines, and show that MgII frequently traces higher velocity gas than FeII. Quantitative morphological parameters derived from the HST imaging suggest that mergers are not a prerequisite for driving outflows. More face-on galaxies also show stronger winds than highly-inclined systems, consistent with the canonical picture of winds emanating perpendicular to galactic disks. Using star-formation rates calculated from GALEX data, and areas estimated from HST imaging, we detect a ~3-sigma correlation between outflow velocity and star-formation rate surface density, but only a weak (~1-sigma) trend between outflow velocity and star-formation rate. Higher resolution data are needed in order to test the scaling relations between outflow velocity and both star-formation rate and star-formation rate surface density predicted by theory.
We present a study of the peculiar Type Ia supernova 2001ay (SN 2001ay). The defining features of its peculiarity are: high velocity, broad lines, and a fast rising light curve, combined with the slowest known rate of decline. It is one magnitude dimmer than would be predicted from its observed value of Delta-m15, and shows broad spectral features. We base our analysis on detailed calculations for the explosion, light curves, and spectra. We demonstrate that consistency is key for both validating the models and probing the underlying physics. We show that this SN can be understood within the physics underlying the Delta-m15 relation, and in the framework of pulsating delayed detonation models originating from a Chandrasekhar mass, white dwarf, but with a progenitor core composed of 80% carbon. We suggest a possible scenario for stellar evolution which leads to such a progenitor. We show that the unusual light curve decline can be understood with the same physics as has been used to understand the Delta-m15 relation for normal SNe Ia. The decline relation can be explained by a combination of the temperature dependence of the opacity and excess or deficit of the peak luminosity, alpha, measured relative to the instantaneous rate of radiative decay energy generation. What differentiates SN 2001ay from normal SNe Ia is a higher explosion energy which leads to a shift of the Ni56 distribution towards higher velocity and alpha < 1. This result is responsible for the fast rise and slow decline. We define a class of SN 2001ay-like SNe Ia, which will show an anti-Phillips relation.
We present Chandra High Resolution Camera observations of CID-42, a candidate recoiling supermassive black hole (SMBH) at z=0.359 in the COSMOS survey. CID-42 shows two optical compact sources resolved in the HST/ACS image embedded in the same galaxy structure and a velocity offset of ~1300 km/s between the H\beta\ broad and narrow emission line, as presented by Civano et al. (2010). Two scenarios have been proposed to explain the properties of CID-42: a GW recoiling SMBH and a double Type 1/ Type 2 AGN system, where one of the two is recoiling because of slingshot effect. In both scenario, one of the optical nuclei hosts an unobscured AGN, while the other one, either an obscured AGN or a star forming compact region. The X-ray Chandra data allow to unambiguously resolve the X-ray emission, and unveil the nature, of the two optical sources in CID-42. We find that only one of the optical nuclei is responsible for the whole X-ray unobscured emission observed and a 3sigma upper limit on the flux of the second optical nucleus is measured. The upper limit on the X-ray luminosity plus the analysis of the multiwavelength spectral energy distribution indicate the presence of a starforming region in the second source rather than an obscured SMBH, thus favoring the GW recoil scenario. However the presence of a very obscured SMBH cannot be fully ruled-out. A new X-ray feature, in a SW direction with respect to the main source, is discovered and discussed.
We present a new stellar dynamical mass measurement of the black hole in the nearby, S0 galaxy NGC 3998. By combining laser guide star adaptive optics observations obtained with the OH-Suppressing Infrared Imaging Spectrograph on the Keck II telescope with long-slit spectroscopy from the Hubble Space Telescope and the Keck I telescope, we map out the stellar kinematics on both small spatial scales, well within the black hole sphere of influence, and on large scales. We find that the galaxy is rapidly rotating and exhibits a sharp central peak in the velocity dispersion. Using the kinematics and the stellar luminosity density derived from imaging observations, we construct three-integral, orbit-based, triaxial stellar dynamical models. We find the black hole has a mass of M_BH = (8.1_{-1.9}^{+2.0}) x 10^8 M_sun, with an I-band stellar mass-to-light ratio of M/L = 5.0_{-0.4}^{+0.3} M_sun/L_sun (3-sigma uncertainties), and that the intrinsic shape of the galaxy is very round, but oblate. With the work presented here, NGC 3998 is now one of a very small number of galaxies for which both stellar and gas dynamical modeling have been used to measure the mass of the black hole. The stellar dynamical mass is nearly a factor of four larger than the previous gas dynamical black hole mass measurement. Given that this cross-check has so far only been attempted on a few galaxies with mixed results, carrying out similar studies in other objects is essential for quantifying the magnitude and distribution of the cosmic scatter in the black hole mass - host galaxy relations.
We present the discovery and spectroscopic follow-up of a nearby late-type L dwarf (2M0614+3950), and two extremely wide very-low-mass binary systems (2M0525-7425AB and 2M1348-1344AB), resulting from our search for common proper motion pairs containing ultracool components in the Two Micron All Sky Survey (2MASS) and the Wide-field Infrared Survey Explorer (WISE) catalogs. The near-infrared spectrum of 2M0614+3950 indicates a spectral type L9 \pm 1 object residing at a distance of 26.1 \pm 1.3 pc. The optical spectrum of the 2M0525-7425 primary reveals an M3.0 \pm 0.5 dwarf, accompanied by a secondary previously classified as L2. The system has an angular separation of ~44", equivalent to ~2000 AU at the 45.7 \pm 2.5 pc distance. Using optical and infrared spectra, respectively, we classify the components of 2M1348-1344AB as M4.5 \pm 0.5 and T6 \pm 1. The angular separation of ~68" is equivalent to ~1300 AU at the distance of 19.2 \pm 0.9 pc. 2M1348-1344AB is one of only five very wide (separation > 1000 AU) systems containing late T dwarfs known to date.
The Kepler-11 star hosts at least six transiting super-Earth planets detected through the precision photometric observations of the KEPLER mission (Lissauer et al.). In this paper, we re-analyze the available KEPLER data, using the direct N-body approach rather than an indirect TTV method in the discovery paper. The orbital modeling in the realm of the direct approach relies on the whole data set, rather than the times of mid-transits only. Most of the results in the original paper are confirmed and extended. We constrained the mass of the outermost planet g to less than 30 Earth masses. The mutual inclinations between orbits b and c as well as between orbits d and e are determined with a good precision, in the range of [1,5] degrees. Having several solutions to four qualitative orbital models of the Kepler-11 system, we analyze its global dynamics with the help of dynamical maps. They reveal very complex structure of the phase space with narrow regions of regular motion. The dynamics are governed by a dense net of three- and four-body mean motion resonances, forming the Arnold web. Overlapping of these resonances is a main source of instability. We found that the Kepler-11 system may be long-term stable only in particular multiple resonant configurations with small relative inclinations. The mass-radius data derived for all companions reveal a clear anti-correlation between the mean density of the planets with their distance from the star. It may reflect the formation and early evolution history of the system.
The Hubble constant Ho describes not only the expansion of local space at redshift z ~ 0, but is also a fundamental parameter determining the evolution of the universe. Recent measurements of Ho anchored on Cepheid observations have reached a precision of several percent. However, this problem is so important that confirmation from several methods is needed to better constrain Ho and, with it, dark energy and the curvature of space. A particularly direct method involves the determination of distances to local galaxies far enough to be part of the Hubble flow through water vapor (H2O) masers orbiting nuclear supermassive black holes. The goal of this article is to describe the relevance of Ho with respect to fundamental cosmological questions and to summarize recent progress of the the `Megamaser Cosmology Project' (MCP) related to the Hubble constant.
The past decade has seen a dramatic improvement in the quality of data available at both high (HE: 100 MeV to 100 GeV) and very high (VHE: 100 GeV to 100 TeV) gamma-ray energies. With three years of data from the Fermi Large Area Telescope (LAT) and deep pointed observations with arrays of Cherenkov telescope, continuous spectral coverage from 100 MeV to $\sim10$ TeV exists for the first time for the brightest gamma-ray sources. The Fermi-LAT is likely to continue for several years, resulting in significant improvements in high energy sensitivity. On the same timescale, the Cherenkov Telescope Array (CTA) will be constructed providing unprecedented VHE capabilities. The optimisation of CTA must take into account competition and complementarity with Fermi, in particularly in the overlapping energy range 10$-$100 GeV. Here we compare the performance of Fermi-LAT and the current baseline CTA design for steady and transient, point-like and extended sources.
One of the main challenges of modern cosmology is to investigate the nature of dark energy in our Universe. The properties of such a component are normally summarised as a perfect fluid with a (potentially) time-dependent equation-of-state parameter $w(z)$. We investigate the evolution of this parameter with redshift by performing a Bayesian analysis of current cosmological observations. We model the temporal evolution as piecewise linear in redshift between `nodes', whose $w$-values and redshifts are allowed to vary. The optimal number of nodes is chosen by the Bayesian evidence. In this way, we can both determine the complexity supported by current data and locate any features present in $w(z)$. We compare this node-based reconstruction with some previously well-studied parameterisations: the Chevallier-Polarski-Linder (CPL) and the Jassal-Bagla-Padmanabhan (JBP) models. By comparing the Bayesian evidence for all of these models we find an indication towards possible time-dependence in the dark energy equation-of-state. It is also worth noting that the CPL and JBP models are significantly disfavoured when compared to our node-based reconstruction and also to a simple cosmological constant $w=-1$.
We propose an alternative, non-singular, cosmic scenario based on gravitationally-induced particle production. The model is an attempt to evade the coincidence and cosmological constant problems of the standard model ($\Lambda$CDM) and also to connect the early and late time accelerating stages of the Universe. Our space-time emerges from a pure initial de Sitter stage thereby providing a natural solution to the horizon problem. Subsequently, due to an instability provoked by the production of massless particles, the Universe evolves smoothly to the standard radiation dominated era thereby ending the production of radiation as required by the conformal invariance. Next, the radiation becomes subdominant with the Universe entering in the cold dark matter dominated era. Finally, the negative pressure associated with the creation of cold dark matter (CCDM model) particles accelerates the expansion and drives the Universe to a final de-Sitter stage. The late time cosmic expansion history of the CCDM model is exactly like in the standard $\Lambda$CDM model, however, there is no dark energy. The model evolves between two limiting (early and late time) de-Sitter regimes. All the stages are also discussed in terms of a scalar field description. This complete scenario is fully determined by two extreme energy densities, or equivalently, the associated de-Sitter Hubble scales connected by $\rho_I/\rho_f=(H_I/H_f)^{2} \sim 10^{122}$, a result that has no correlation with the cosmological constant problem. We also study the linear growth of matter perturbations at the final accelerating stage. It is found that the growth index can be written as a function of the $\Lambda$ growth index, $\gamma_{\Lambda} \simeq 6/11$. Performing a $\chi^{2}$ statistical test we show that the CCDM model provides growth rates that match sufficiently well with the observed growth rate of structure.
(abridged) Pulsar activity and its related radiation mechanism are usually
explained by invoking some plasma processes occurring inside the magnetosphere.
Despite many detailed local investigations, the global electrodynamics around
those neutron stars remains poorly described. Better understanding of these
compact objects requires a deep and accurate knowledge of their immediate
electromagnetic surrounding within the magnetosphere and its link to the
relativistic pulsar wind.
The aim of this work is to present accurate solutions to the nearly
stationary force-free pulsar magnetosphere and its link to the striped wind,
for various spin periods and arbitrary inclination. To this end, the
time-dependent Maxwell equations are solved in spherical geometry in the
force-free approximation using a vector spherical harmonic expansion of the
electromagnetic field. An exact analytical enforcement of the divergenceless of
the magnetic part is obtained by a projection method. Special care has been
given to design an algorithm able to look deeply into the magnetosphere with
physically realistic ratios of stellar $R_*$ to light-cylinder $\rlight$
radius. We checked our code against several analytical solutions, like the
Deutsch vacuum rotator solution and the Michel monopole field. We also retrieve
energy losses comparable to the magneto-dipole radiation formula and consistent
with previous similar works. Finally, for arbitrary obliquity, we give an
expression for the total electric charge of the system. It does not vanish
except for the perpendicular rotator. This is due to the often ignored point
charge located at the centre of the neutron star. It is questionable if such
solutions with huge electric charges could exist in reality except for
configurations close to an orthogonal rotator. The charge spread over the
stellar crust is not a tunable parameter as is often hypothesized.
Quasi-periodic disturbances have been observed in the outer solar atmosphere for many years now. Although first interpreted as upflows (Schrijver et al. (1999)), they have been widely regarded as slow magnetoacoustic waves, due to observed velocities and periods. However, recent observations have questioned this interpretation, as periodic disturbances in Doppler velocity, line width and profile asymmetry were found to be in phase with the intensity oscillations (De Pontieu et al. (2010),Tian1 et al. (2011))}, suggesting the disturbances could be quasi-periodic upflows. Here we conduct a detailed analysis of the velocities of these disturbances across several wavelengths using the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We analysed 41 examples, including both sunspot and non sunspot regions of the Sun. We found that the velocities of propagating disturbances (PDs) located at sunspots are more likely to be temperature dependent, whereas the velocities of PDs at non sunspot locations do not show a clear temperature dependence. We also considered on what scale the underlying driver is affecting the properties of the PDs. Finally, we found that removing the contribution due to the cooler ions in the 193 A wavelength suggests that a substantial part of the 193 emission of sunspot PDs can be contributed to the cool component of 193\AA.
Carbon rich stars of Population II, such as CH giants, can provide direct information on the role of low to intermediate mass stars of the Halo in early Galactic evolution. Moreover, accurate knowledge of the CH stellar population is a critical requirement for building up scenarios for early Galactic chemical evolution. The first list of the faint high latitude C stars (FHLCs), found in the Digitized First Byurakan Survey {this http URL and this http URL} (DFBS) is given in a paper recently submitted for publication in Astronomy ad Astrophysics. In the present work, we report the recent discovery of two additional CH type stars (not previously catalogued), namely DFBS J075331.98+190344.3 and DFBS J111422.94+091442.7, detected on the DFBS plates with help of the image analysis softwares (FITSView and SAOImage DS9). Medium resolution spectra confirm the C rich nature for both of them. Using infrared color magnitudes relationship, we estimated the distances and K band absolute magnitudes of the new objects.
GALEX J215818.5+241924 was initially identified as a possible nova in Pegasus. We report unfiltered photometry of the object which revealed the presence of superhumps, with peak-to-peak amplitude of up to 0.22 magnitudes, diagnostic of it being a member of the SU UMa family of dwarf novae. The outburst amplitude was 4.3 magnitudes and it lasted at least 10 days, with a maximum brightness of magnitude 14.3. We determined the mean superhump period from our first 5 nights of observations as Psh = 0.06728(21) d. However analysis of the O-C residuals showed a dramatic evolution in Psh during the outburst. During the first part of the plateau phase the period increased with dPsh/dt = +2.67(15) \times 10-4. There was then an abrupt change following which the period decreased with dPsh/dt = -2.08(9)\times10-4. We found a signal in the power spectrum of the photometry which we interpret as the orbital signal with Porb = 0.06606(35) d. Thus the superhump period excess was epsilon = 0.020(8), such value being consistent with other SU UMa systems of similar orbital period.
We analyze the role of bars in the build-up of central mass concentrations in massive, disk galaxies. Our parent sample consists of 3757 face-on disk galaxies with redshifts between 0.01 and 0.05, selected from the seventh Data Release of the Sloan Digital Sky Survey. 1555 galaxies with bars are identified using position angle and ellipticity profiles of the $i$-band light. We compare the ratio of the specific star formation rate measured in the 1-3 kpc central region of the galaxy to that measured for the whole galaxy. Galaxies with strong bars have centrally enhanced star formation; the degree of enhancement depends primarily on the ellipticity of the bar, and not on the size of the bar or on the mass or structure of the host galaxy. The fraction of galaxies with strong bars is highest at stellar masses greater than $3 \times 10^{10} M_{\odot}$, stellar surface densities less than $3 \times 10^8 M_{\odot}$ and concentration indices less than 2.5. In this region of parameter space, galaxies with strong bars either have enhanced central star formation rates, or star formation that is {\em suppressed} compared to the mean. This suggests that bars may play a role in the eventual quenching of star formation in galaxies. Only 50% of galaxies with strongly concentrated star formation have strong bars, indicating that other processes such as galaxy interactions also induce central star-bursts. We also find that the ratio of the size of the bar to that of the disk depends mainly on the colour of the galaxy, suggesting that the growth and destruction of bars are regulated by gas accretion, as suggested by simulations.
Magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere. Alfven waves and magneto-sonic waves are particular classes of MHD waves. These wave modes are clearly different and have pure properties in uniform plasmas of infinite extent only. Due to plasma non-uniformity MHD waves have mixed properties and cannot be classified as pure Alfven or magneto-sonic waves. However, vorticity is a quantity unequivocally related to Alfven waves as compression is for magneto-sonic waves. Here, we investigate MHD waves superimposed on a one-dimensional non-uniform straight cylinder with constant magnetic field. For a piecewise constant density profile we find that the fundamental radial modes of the non-axisymmetric waves have the same properties as surface Alfven waves at a true discontinuity in density. Contrary to the classic Alfveen waves in a uniform plasma of infinite extent, vorticity is zero everywhere except at the cylinder boundary. If the discontinuity in density is replaced with a continuous variation of density, vorticity is spread out over the whole interval with non-uniform density. The fundamental radial modes of the non-axisymmetric waves do not need compression to exist unlike the radial overtones. In thin magnetic cylinders the fundamental radial modes of the non-axisymmetric waves with phase velocities between the internal and the external Alfven velocities can be considered as surface Alfven waves. On the contrary, the radial overtones can be related to fast-like magneto-sonic modes.
Strong Halpha Emitters (HAEs) dominate the z~4 Lyman-break galaxy population. We have identified local analogs of these HAEs using the Sloan Digital Sky Survey (SDSS). At z<0.4, only 0.04% of galaxies are classified as HAEs with Halpha equivalent widths (>500A) comparable to that of z~4 HAEs. Local HAEs have lower stellar mass and lower ultraviolet (UV) luminosity than z~4 HAEs, yet the Halpha-to-UV luminosity ratio as well as their specific star-formation rate is consistent with that of z~4 HAEs indicating that they are scaled down versions of high-z star-forming galaxies. Compared to the previously studied local analogs of z~2 Lyman break galaxies selected using rest-frame UV, local HAEs show similar UV luminosity surface density, weaker Dn(4000) breaks, lower metallicity and lower stellar mass. This supports the idea that local HAEs are less evolved galaxies than the traditional Lyman break analogs. We are not able to constrain if the star-formation history in local HAEs is powered by mergers or by cosmological cold flow accretion. However, in the stacked spectrum, local HAEs show a strong HeII4686 emission line suggesting a population of young (<10Myr), hot, massive stars similar to that seen in some Wolf-Rayet galaxies. Low [NII]/[OIII] line flux ratios imply that local HAEs are inconsistent with being systems that host bright AGN. Instead, it is highly likely that local HAEs are galaxies with an elevated ionization parameter, either due to a high electron density or large escape fraction of hydrogen ionizing photons as in the case for Wolf-Rayet galaxies.
Our aim is to identify and classify mean-motion resonances (MMRs) for the coplanar circular restricted three-body problem (CR3BP) for mass ratios between 0.10 and 0.50. Our methods include the maximum Lyapunov exponent, which is used as an indicator for the location of the resonances, the Fast Fourier Transform (FFT) used for determining what kind of resonances are present, and the inspection of the orbital elements to classify the periodicity. We show that the 2:1 resonance occurs the most frequently. Among other resonances, the 3:1 resonance is the second most common, and furthermore both 3:2 and 5:3 resonances occur more often than the 4:1 resonance. Moreover, the resonances in the coplanar CR3BP are classified based on the behaviour of the orbits. We show that orbital stability is ensured for high values of resonance (i.e., high ratios) where only a single resonance is present. The resonances attained are consistent with the previously established resonances for the Solar System, i.e., specifically, in regards to the asteroid belt. Previous work employed digital filtering and Lyapunov characteristic exponents to determine stochasticity of the eccentricity, which is found to be consistent with our usage of Lyapunov exponents as an alternate approach based on varying the mass ratio instead of the eccentricity. Our results are expected to be of principal interest to future studies, including augmentations to observed or proposed resonances, of extra-solar planets in binary stellar systems.
We present Chandra X-ray and VLA radio observations of the radio galaxy 3C305. The X-ray observations reveal the details of the previously known extended X-ray halo around the radio galaxy. We show using X-ray spectroscopy that the X-ray emission is consistent with being shock-heated material and can be modelled with standard collisional-ionization models, rather than being photoionized by the active nucleus. On this basis, we can make a self-consistent model in which the X-ray-emitting plasma is responsible for the depolarization of some regions of the radio emission from the jets and hotspots, and to place lower and upper limits on the magnetic field strength in the depolarizing medium. On the assumption that the X-ray-emitting material, together with the previously-known extended emission-line region and the outflow in neutral hydrogen, are all being driven out of the centre of the galaxy by an interaction with the jets, we derive a detailed energy budget for the radio galaxy, showing that the X-ray-emitting gas dominates the other phases in terms of its energy content. The power supplied by the jets must be ~ 10^43 erg/s.
Type Ia supernovae are bright stellar explosions distinguished by standardizable light curves that allow for their use as distance indicators for cosmological studies. Despite their highly successful use in this capacity, the progenitors of these events are incompletely understood. We describe simulating type Ia supernovae in the paradigm of a thermonuclear runaway occurring in a massive white dwarf star. We describe the multi-scale physical processes that realistic models must incorporate and the numerical models for these that we employ. In particular, we describe a flame-capturing scheme that addresses the problem of turbulent thermonuclear combustion on unresolved scales. We present the results of our study of the systematics of type Ia supernovae including trends in brightness following from properties of the host galaxy that agree with observations. We also present performance results from simulations on leadership-class architectures.
Two years of neutral measurements by IBEX-Lo have yielded several direct observations of interstellar neutral helium and oxygen during preferred viewing seasons. Besides the interstellar signal, there are indications of the presence of secondary neutral helium and oxygen created in the heliosphere. Detailed modeling of these particle species is necessary to connect the measured fluxes to the pristine local interstellar medium while accounting for loss and production of neutral particles during their path through the heliosphere. In this contribution, global heliosphere models are coupled to analytic calculations of neutral trajectories to obtain detailed estimates of the neutral distribution function of primary interstellar helium atoms in the heliosphere, in particular in the inner heliosphere.
The G0V dwarf TrES-2A, which is transited by a hot Jupiter, is one of the main short-cadence targets of the Kepler telescope and, therefore, among the photometrically best-studied planetary systems known today. Given the near-grazing geometry of the planetary orbit, TrES-2 offers an outstanding opportunity to search for changes in its orbital geometry. Our study focuses on the secular change in orbital inclination reported in previous studies. We present a joint analysis of the first four quarters of Kepler photometry together with the publicly available ground-based data obtained since the discovery of TrES-2b in 2006. We use a common approach based on the latest information regarding the visual companion of TrES-2A and stellar limb darkening to further refine the orbital parameters. We find that the Kepler observations rule out a secular inclination change of previously claimed order as well as variations of the transit timing, however, they also show slight indication for further variability in the inclination which remains marginally significant.
We constrain a unified dark matter (UDM) model from the latest observational data. This model assumes that the dark sector is degenerate. Dark energy and dark matter are the same component. It can be described by an affine equation of state $P_X= p_0 +\alpha \rho_X$. Our data set contains the newly revised $H(z)$ data, type Ia supernovae (SNe Ia) from Union2 set, baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample, as well as the cosmic microwave background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) results. By using the Markov Chain Monte Carlo (MCMC) method, we obtain the results in a flat universe: $\Omega_\Lambda$=$0.719_{-0.0305}^{+0.0264}(1\sigma)_{-0.0458}^{+0.0380}(2\sigma)$, $\alpha$=$1.72_{-4.79}^{+3.92}(1\sigma)_{-7.30}^{+5.47}(2\sigma)(\times10^{-3})$, $\Omega_bh^2$=$0.0226_{-0.0011}^{+0.0011}(1\sigma)_{-0.0015}^{+0.0016}(2\sigma)$. Moreover, when considering a non-flat universe, $\Omega_\Lambda$=$0.722_{-0.0447}^{+0.0362}(1\sigma)_{-0.0634}^{+0.0479}(2\sigma)$, $\alpha$=$0.242_{-0.775}^{+0.787}(1\sigma)_{-1.03}^{+1.10}(2\sigma)(\times10^{-2})$, $\Omega_bh^2$=$0.0227_{-0.0014}^{+0.0015}(1\sigma)_{-0.0018}^{+0.0021}(2\sigma)$, $\Omega_k$=$-0.194_{-1.85}^{+2.02}(1\sigma)_{-2.57}^{+2.75}(2\sigma)(\times10^{-2})$. These give a more stringent results than before. We also give the results from other combinations of these data for comparison. The observational Hubble parameter data can give a more stringent constraint than SNe Ia. From the constraint results, we can see the parameters $\alpha$ and $\Omega_k$ are very close to zero, which means a flat universe is strongly supported and the speed of sound of the dark sector seems to be zero.
Directional detection is a promising Dark Matter search strategy. Even though it could accommodate to a sizeable background contamination, electron/recoil discrimination remains a key and challenging issue as for direction-insensitive detectors. The measurement of the 3D track may be used to discriminate electrons from nuclear recoils. While a high rejection power is expected above 20 keV ionization, a dedicated data analysis is needed at low energy. After identifying discriminant observables, a multivariate analysis, namely a Boosted Decision Tree, is proposed, enabling an efficient event tagging for Dark Matter search. We show that it allows us to optimize rejection while keeping a rather high efficiency which is compulsory for rare event search.With respect to a sequential analysis, the rejection is about 20 times higher with a multivariate analysis, for the same Dark Matter exclusion limit.
Young, OB-type candidates are identified in a ~7900 sq-deg. region encompassing the Large and Small Magellanic Clouds (LMC/SMC) periphery, the Bridge, part of the Magellanic Stream (MS) and Leading Arm (LA). Selection is based on UV, optical and IR photometry from existing large-area surveys and proper motions from the Southern Proper Motion 4 catalog (SPM4). The spatial distribution of these young star candidates shows: 1) a well-populated SMC wing which continues westward with two branches partially surrounding the SMC, 2) a rather narrow path from the SMC wing eastward toward the LMC which is offset by 1 to 2 deg. from the high-density H I ridge in the Bridge, 3) a well-populated periphery of the LMC dominated by clumps of stars at the ends of the LMC bar and 4) a few scattered candidates in the MS and two overdensities in the LA regions above and below the Galactic plane. Additionally, a proper-motion analysis is made of a radial-velocity selected sample of red giants and supergiants in the LMC, previously shown to be a kinematically and chemically distinct subgroup, most likely captured from the SMC. SPM4 proper motions of these stars also indicate they are distinct from the LMC population. The observational results presented here, combined with the known orbits of the Clouds, and other aspects of the LMC morphology, suggest an off-center, moderate to highly-inclined collision between the SMC and the LMC's disk that took place between 100 and 200 Myr ago.
We used the Project 1640 near-infrared coronagraph and integral field spectrograph to observe 19 young solar type stars. Five of these stars are known binary stars and we detected the late-type secondaries and were able to measure their JH spectra with a resolution of R\sim30. The reduced, extracted, and calibrated spectra were compared to template spectra from the IRTF spectral library. With this comparison we test the accuracy and consistency of spectral type determination with the low-resolution near-infrared spectra from P1640. Additionally, we determine effective temperature and surface gravity of the companions by fitting synthetic spectra calculated with the PHOENIX model atmosphere code. We also present several new epochs of astrometry of each of the systems. Together these data increase our knowledge and understanding of the stellar make up of these systems. In addition to the astronomical results, the analysis presented helps validate the Project 1640 data reduction and spectral extraction processes and the utility of low-resolution, near-infrared spectra for characterizing late-type companions in multiple systems.
The astronomical dark matter could be made of weakly interacting and massive particles. If so, these species would be abundant inside the Milky Way, where they would continuously annihilate and produce cosmic rays. Those annihilation products are potentially detectable at the Earth, and could provide indirect clues for the presence of dark matter species within the Galaxy. We will review here the various cosmic radiations which the dark matter can produce. We will examine how they propagate throughout the Milky Way and compare the dark matter yields with what pure astrophysical processes are expected to generate. The presence of dark matter substructures might enhance the signals and will be briefly discussed.
We report the discovery of 6 SX Phoenicis stars in the southern globular cluster NGC 4833. Images were obtained from January through June 2011 with the Southeastern Association for Research in Astronomy 0.6 meter telescope located at Cerro Tololo Interamerican Observatory. The image subtraction method of Alard & Lupton (1998)was used to search for variable stars in the cluster. We confirmed 17 previously cataloged variables by Demers & Wehlau(1977). In addition to the previously known variables we have identified 10 new variables. Of the total number of confirmed variables in our 10x10 arcmin^2 field, we classified 10 RRab variables, with a mean period of 0.69591 days, 7 RRc, with a mean period of 0.39555 days, 2 possible RRe variables with a mean period of 0.30950 days, a W Ursae Majoris contact binary, an Algol-type binary, and the 6 SX Phoenicis stars with a mean period of 0.05847 days. The periods, relative numbers of RRab and RRc variables, and Bailey diagram are indicative of the cluster being of the Oosterhoff type II. We present the phased-light curves, periods of previously known variables and the periods and classifications of the newly discovered variables, and their location on the color-magnitude diagram.
Using a 3D MHD simulation, we model the quasi-static evolution and the onset of eruption of a coronal flux rope. The simulation begins with a twisted flux rope emerging at the lower boundary and pushing into a pre-existing coronal potential arcade field. At a chosen time the emergence is stopped with the lower boundary taken to be rigid. Then the coronal flux rope settles into a quasi-static rise phase with an underlying, central sigmoid-shaped current layer developing. Reconnections in the dissipating current layer during the quasi-static phase effectively add twisted flux to the flux rope and thus allow it to rise quasi-statically, even though the magnetic energy is decreasing as the system relaxes. We examine the thermal features produced by such "tether-cutting" reconnections as a result of heating and field aligned thermal conduction. It is found that a central hot, low-density channel containing reconnected, twisted flux threading under the flux rope axis forms on top of the central current layer. When viewed in the line of sight roughly aligned with the hot channel (which is roughly along the neutral line), the central current layer appears as a high-density vertical column with upward extensions as a "U" shaped dense shell enclosing a central hot, low-density void. Such thermal features have been observed within coronal prominence cavities. Our MHD simulations suggest that they are the signatures and consequences of the tether-cutting reconnections, and that the central void grows and rises with the reconnections, until the flux rope reaches the critical height for the onset of the torus instability and dynamic eruption ensues.
Using the Southeastern Association for Research in Astronomy 0.6 meter telescope located at Cerro Tololo, we searched for variable stars in the southern globular cluster NGC 6584. We obtained images during 8 nights between 28 May and 6 July of 2011. After processing the images, we used the image subtraction package ISIS developed by Alard (2000)to search for the variable stars. We identified a total of 69 variable stars in our 10x10 arcmin^2 field, including 43 variables cataloged by Millis & Liller (1980) and 26 hereto unknown variables. In total, we classified 46 of the variables as type RRab, with a mean period of 0.56776 days, 15 as type RRc with a mean period of 0.30886 days, perhaps one lower amplitude type RRe, with a period of 0.26482 days, 4 eclipsing binaries, and 3 long period (P > 2 days) variable stars. As many as 15 of the RRab Lyrae stars exhibited the Blazhko Effect. Furthermore, the mean periods of the RR Lyrae types, the exhibited period/amplitude relationship, and the ratio of N_c/(N_ab+N_c) of 0.25 are consistent with an Oosterhoff Type I cluster. Here we present refined periods, V-band light curves, and classifications for each of the 69 variables, as well as a color-magnitude diagram of the cluster.
Debris disks with extremely large infrared excesses (fractional luminosities $> 10^{-2}$) are rare. Those with ages between 30 and 130 Myr are of interest because their evolution has progressed well beyond that of protoplanetary disks (which dissipate with a timescale of order 3 Myr), yet they represent a period when dynamical models suggest that terrestrial planet building may still be progressing through large, violent collisions that could yield large amounts of debris and large infrared excesses. For example, our Moon was formed through a violent collision of two large proto-planets during this age range. We report two disks around the solar-like stars ID8 and HD 23514 in this age range where the 24 {\mu}m infrared excesses vary on timescales of a few years, even though the stars are not variable in the optical. Variations this rapid are difficult to understand if the debris is produced by collisional cascades, as it is for most debris disks. It is possible that the debris in these two systems arises in part from condensates from silicate-rich vapor produced in a series of violent collisions among relatively large bodies. If their evolution is rapid, the rate of detection of extreme excesses would indicate that major collisions may be relatively common in this age range.
I review here the present observational efforts to study parsec-scale radio jets in active galactic nuclei with very-long-baseline interferometry (VLBI) as related to the new window to the Universe opened by the LAT instrument on-board the Fermi Gamma-Ray Space Telescope. I describe the goals and achievements of those radio studies, which aim to probe the emission properties, morphological changes and related kinematics, magnetic fields from the linear and circular polarization, etc., and I put those in the context of the radio--gamma-ray connection. Both statistical studies based on radio surveys and individual studies on selected sources are reported. Those should shed some light in the open questions about the nature of emission in blazars.
In this paper we explore the impact of including redshift information on cosmological applications with the forthcoming generation of large-scale, deep radio continuum surveys. By cross-matching these radio surveys with shallow optical to near-infrared surveys we can essentially separate the source distribution into a low redshift sample and the high-z tail of the radio sources that are unidentified, thus providing a constraint on the evolution of cosmological parameters such as those of dark energy. We examine two radio surveys, the Evolutionary Map of the Universe (EMU) and the Westerbork Observations of the Deep APERTIF Northern sky (WODAN). A crucial advantage is their combined potential to provide a deep, full-sky survey. The surveys used for the cross-identifications are SkyMapper and SDSS, for the southern and northern skies, respectively. We concentrate on the galaxy clustering angular power spectrum as our benchmark observable and find that the possibility of including this low redshift information yields major improvements in the results. With this approach, we are able to put strict constraints on the dark energy parameters, i.e. w_0=-0.9+/-0.065(0.087) and w_a=-0.24+/-0.19(0.26) with(without) priors from Planck; this corresponds to a Figure of Merit (FoM) of circa 400(>200), which is two to three orders of magnitude times better than the case without any redshift information and more than three times better than what obtained by using only the cross-identified sources.
We have developed a set of dynamically evolving Fokker-Planck models for the collapsed-core globular star cluster M15, which directly address the issue of whether a central black hole is required to fit Hubble Space Telescope (HST) observations of the stellar spatial distribution and kinematics. As in our previous work reported by Dull et al., we find that a central black hole is not needed. Using local mass-function data from HST studies, we have also inferred the global initial stellar mass function. As a consequence of extreme mass segregation, the local mass functions differs from the global mass function at every location. In addition to reproducing the observed mass functions, the models also provide good fits to the star-count and velocity-dispersion profiles, and to the millisecond pulsar accelerations. We address concerns about the large neutron star populations adopted in our previous Fokker-Planck models for M15. We find that good model fits can be obtained with as few as 1600 neutron stars; this corresponds to a retention fraction of 5% of the initial population for our best fit initial mass function. The models contain a substantial population of massive white dwarfs, that range in mass up to 1.2 solar masses. The combined contribution by the massive white dwarfs and neutron stars provides the gravitational potential needed to reproduce HST measurements of the central velocity dispersion profile.
The present work is devoted to the detection of monochromatic gravitational waves signals from pulsars using the ALLEGRO's data detector. In this work we will present the region (in frequency) of millisecond pulsars of the 47 Tucanae (NGC 104) in the band of detector. According with this result was possible to analyse the frequency of the pulsar J1748-2446L and J1342+2822c, searching annual Doppler variations using power spectrum estimates for the year 1999. We tested this method injecting a simulated signal in real data and we were able to detect it.
Higher derivative scalar field theories have received considerable attention for the potentially explanations of the initial state of the universe or the current cosmic acceleration which they might offer. They have also attracted many interests in the phenomenological studies of infrared modifications of gravity. These theories are mostly studied by the metric variational approach in which only the metric is the fundamental field to account for the gravitation. In this paper we study the higher derivative scalar fields with the metric-affine formalism where the connections are treated arbitrarily at the beginning. Because the higher derivative scalar fields couple to the connections directly in a covariant theory these two formalisms will lead to different results. These differences are suppressed by the powers of the Planck mass and are usually expected to have small effects. But in some cases they may cause non-negligible deviations. We show by a higher derivative dark energy model that the two formalisms lead to significantly different pictures of the future universe.
We investigate the viability of having dark matter in the minimal left-right symmetric theory. We find the lightest right-handed neutrino with a mass around keV as the only viable candidate consistent with a TeV scale of left-right symmetry. In order to account for the correct relic density with such low scales, the thermal overproduction of the dark matter in the early universe is compensated by a sufficient late entropy production due to late decay of heavier right-handed neutrinos. We point out that the presence of the right-handed charge-current interactions, operative around the QCD phase transition, has a crucial impact on the amount of dilution, as does the nature of the phase transition itself. A careful numerical study, employing the Boltzmann equations, reveals the existence of a narrow window for the right-handed gauge boson mass, possibly within the reach of LHC (in disagreement with a previous study). We also elaborate on a variety of astrophysical, cosmological and low energy constraints on this scenario.
Using constraints on the pure neutron matter (PNM) equation of state (EoS) from recent \emph{ab initio} calculations, we present a general optimization of the pure isovector parameters of the popular relativistic mean-field (RMF) and Skyrme-Hartree-Fock (SHF) nuclear energy-density functionals (EDFs) while maintaining the broad quality of the predictions for binding energies and charge radii of nuclei. Such optimization leads to broadly consistent and tight predictions of the symmetry energy $J$ and its slope parameter $L$ at saturation density with associated joint 1$\sigma$ confidence ellipses in the $J-L$ plane. We demonstrate that given this optimization, the resulting neutron skin thicknesses are consistent with the experimental data so far, but clear model dependence shows up in (a) the slope of the correlation between $J$ and $L$ from the confidence ellipse, (b) the curvature parameter of the symmetry energy $K_{\rm sym}$, (c) the symmetry energy at supra-saturation densities, and (d) the neutron star radius. Notably, the RMF and SHF models are shown to be only marginally consistent at best with constraints on the isospin-dependent part of the incompressibility of neutron-rich nuclear matter $K_{\tau}$, and that the model dependence can lead to about 1 km difference of the neutron star radius given the same values of $J$, $L$ and symmetric nuclear matter (SNM) saturation properties.
The reader can find in the literature a lot of different techniques to study
the dynamics of a given system and also, many suitable numerical integrators to
compute them. Notwithstanding the recent work of Maffione et al. (2011a) for
mappings, a detailed comparison among the widespread indicators of chaos in a
general system is still lacking. Such a comparison could lead to select the
most efficient algorithms given a certain dynamical problem. Furthermore, in
order to choose the appropriate numerical integrators to compute them, more
comparative studies among numerical integrators are also needed.
This work deals with both problems. We first extend the work of Maffione et
al. (2011) for mappings to the 2D H\'enon & Heiles (1964) potential, and
compare several variational indicators of chaos: the Lyapunov Indicator (LI);
the Mean Exponential Growth Factor of Nearby Orbits (MEGNO); the Smaller
Alignment Index (SALI) and its generalized version, the Generalized Alignment
Index (GALI); the Fast Lyapunov Indicator (FLI) and its variant, the Orthogonal
Fast Lyapunov Indicator (OFLI); the Spectral Distance (D) and the Dynamical
Spectras of Stretching Numbers (SSNs). We also include in the record the
Relative Lyapunov Indicator (RLI), which is not a variational indicator as
the others. Then, we test a numerical technique to integrate
Ordinary Differential Equations (ODEs) based on the Taylor method implemented
by Jorba & Zou (2005) (called taylor), and we compare its performance with
other two well-known efficient integrators: the Prince & Dormand (1981)
implementation of a Runge-Kutta of order 7-8 (DOPRI8) and a Bulirsch-St\"oer
implementation. These tests are run under two very different systems from the
complexity of their equations point of view: a triaxial galactic potential
model and a perturbed 3D quartic oscillator.
T. H. Astbury (1858-1922) was for many years the much-respected headmaster of a boys' junior school in the English market town of Wallingford. By night he was a dedicated amateur astronomer who enjoyed observing meteors, variable stars and many other objects. He began to search few new variable stars, his first discovery being the bright Cepheid variable, RT Aurigae. This, along with his discovery of 4 other variable stars, brought him to attention of some of the most famous professional astronomers of the age, including Herbert Hall Turner, Frank Dyson and Arthur Eddington.
A new sampling theorem on the sphere has been developed recently, reducing the number of samples required to represent a band-limited signal by a factor of two for equiangular sampling schemes. For signals sparse in a spatially localised measure, such as in a wavelet basis, overcomplete dictionary, or in the magnitude of their gradient, for example, a reduction in the number of samples required to represent a band-limited signal has important implications for sparse signal reconstruction on the sphere. A more efficient sampling of the sphere improves the fidelity of sparse signal reconstruction through both the dimensionality and spatial sparsity of signals. To demonstrate this result we consider a simple inpainting problem on the sphere and consider signals sparse in the magnitude of their gradient. We develop a framework for total variation (TV) inpainting on the sphere by making a connection to the underlying continuous signal via a sampling theorem. Numerical simulations are performed, verifying the enhanced fidelity of sparse signal reconstruction due to the more efficient sampling of the sphere provided by the new sampling theorem.
We analyze publicly available Fermi-LAT high-energy gamma-ray data and confirm the existence of clear spectral feature peaked at $E_\gamma= 130$ GeV. Scanning over the Galaxy we identify several disconnected regions where the observed excess originates from. Our best optimized fit is obtained for the central region of Galaxy with a clear peak at 130 GeV with statistical significance $4.5\sigma ,$ while for the other regions the peak significances vary between $3.2\sigma$ and $1.6\sigma.$ The observed excess is not correlated with Fermi bubbles. We compute the photon spectra induced by dark matter annihilations into two and four standard model particles, the latter via two light intermediate states, and fit the spectra with data. Since our fits indicate sharper and higher signal peak than in the previous works, data disfavours all but the dark matter direct two-body annihilation channels into photons. Due to the final state radiation our fits prefer dark matter mass 145 GeV for the $\gamma\gamma$ channel. We obtain large gamma-ray fluxes from Galactic centre that imply large annihilation cross-sections of order thermal freeze-out cross-section, if the Einasto halo profile correctly predicts the central cusp. If the observed gamma-ray excess comes from dark matter annihilations, we have identified the most dense dark matter sub-structures of our Galaxy. The large dark matter two-body annihilation cross-section to photons may signal a new resonance that should be searched for at the CERN LHC experiments.
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Stars destroy lithium (Li) in their normal evolution. The convective envelopes of evolved red giants reach temperatures of millions of K, hot enough for the 7Li(p,alpha)4He reaction to burn Li efficiently. Only about 1% of first-ascent red giants more luminous than the luminosity function bump in the red giant branch exhibit A(Li) > 1.5. Nonetheless, Li-rich red giants do exist. We present 15 Li-rich red giants--14 of which are new discoveries--among a sample of 2054 red giants in Milky Way dwarf satellite galaxies. Our sample more than doubles the number of low-mass, metal-poor ([Fe/H] <~ -0.7) Li-rich red giants, and it includes the most-metal poor Li-enhanced star known ([Fe/H] = -2.82, A(Li)_NLTE = 3.15). Because most of these stars have Li abundances larger than the universe's primordial value, the Li in these stars must have been created rather than saved from destruction. These Li-rich stars appear like other stars in the same galaxies in every measurable regard other than Li abundance. We consider the possibility that Li enrichment is a universal phase of evolution that affects all stars, and it seems rare only because it is brief.
Identifying liquid water on the surface of planets is a high priority, as this traditionally defines habitability. One proposed signature of oceans is specular reflection ("glint"), which increases the apparent albedo of a planet at crescent phases. We post-process a global climate model of an Earth-like planet to simulate reflected lightcurves. Significantly, we obtain glint-like phase variations even though we do not include specular reflection in our model. This false positive is the product of two generic properties: 1) for modest obliquities, a planet's poles receive less orbit-averaged stellar flux than its equator, so the poles are more likely to be covered in highly reflective snow and ice, and 2) we show that reflected light from a modest-obliquity planet at crescent phases probes higher latitudes than at gibbous phases, therefore a planet's apparent albedo will naturally increase at crescent phase. We suggest that this "latitude-albedo effect" will operate even for large obliquities: in that case the equator receives less orbit-averaged flux than the poles, and the equator is preferentially sampled at crescent phase. Using rotational and orbital color variations to map the surfaces of directly imaged planets and estimate their obliquity will therefore be a necessary pre-condition for properly interpreting their reflected phase variations. The latitude-albedo effect is a particularly convincing glint false positive for zero-obliquity planets, and such worlds are not amenable to latitudinal mapping. This effect severely limits the utility of specular reflection for detecting oceans on exoplanets.
We examine a low energy mechanism for the transfer of meteoroids between two planetary systems embedded in a star cluster using quasi-parabolic orbits of minimal energy. Using Monte Carlo simulations, we find that the exchange of meteoroids could have been significantly more efficient than previously estimated. Our study is relevant to astrobiology as it addresses whether life on Earth could have been transferred to other planetary systems in the solar system's birth cluster and whether life on Earth could have been transferred here from beyond the solar system. In the solar system, the timescale over which solid material was delivered to the region from where it could be transferred via this mechanism likely extended to several hundred million years (as indicated by the 3.8-4.0 Ga epoch of the Late Heavy Bombardment). This timescale could have overlapped with the lifetime of the Solar birth cluster (~100-500 Myr). Therefore, we conclude that lithopanspermia is an open possibility if life had an early start. Adopting parameters from the minimum mass solar nebula, considering a range of planetesimal size distributions derived from observations of asteroids and Kuiper Belt Objects and theoretical coagulation models, and taking into account Oort Cloud formation models, the expected number of bodies with mass > 10 kg that could have been transferred between the Sun and its nearest cluster neighbor could be of the order of 1E14-3E16, with transfer timescales of 10s Myr. We estimate that of the order of 3E8 x l(km) could potentially be life-bearing, where l(km) is the depth of the Earth crust in km that was ejected as the result of the early bombardment.
The COSMOS field has been the subject of a wide range of observations, with a number of studies focusing on reconstructing the 3D dark matter density field. Typically, these studies have focused on one given method or tracer. In this paper, we reconstruct the distribution of mass in the COSMOS field out to a redshift z=1 by combining Hubble Space Telescope weak lensing measurements with zCOSMOS spectroscopic measurements of galaxy clustering. The distribution of galaxies traces the distribution of mass with high resolution (particularly in redshift, which is not possible with lensing), and the lensing data empirically calibrates the mass normalisation (bypassing the need for theoretical models). Two steps are needed to convert a galaxy survey into a density field. The first step is to create a smooth field from the galaxy positions, which is a point field. We investigate four possible methods for this: (i) Gaussian smoothing, (ii) convolution with truncated isothermal sphere, (iii) fifth nearest neighbour smoothing and (iv) a muliti-scale entropy method. The second step is to rescale this density field using a bias prescription. We calculate the optimal bias scaling for each method by comparing predictions from the smoothed density field with the measured weak lensing data, on a galaxy-by-galaxy basis. In general, we find scale-independent bias for all the smoothing schemes, to a precision of 10%. For the nearest neighbour smoothing case, we find the bias to be 2.51\pm 0.25. We also find evidence for a strongly evolving bias, increasing by a factor of ~3.5 between redshifts 0<z<0.8. We believe this strong evolution can be explained by the fact that we use a flux limited sample to build the density field.
Small amounts of star formation in elliptical galaxies are suggested by several results: surprisingly young ages from optical line indices, cooling X-ray gas, and mid-IR dust emission. Such star formation has previously been difficult to detect, but using UV Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) imaging, we have identified individual young stars and star clusters in four nearby ellipticals. This technique is orders of magnitude more sensitive than other methods, allowing detections of star formation to 10^{-5} Msun/yr. Ongoing star formation is detected in all galaxies, including three ellipticals that have previously exhibited potential signposts of star forming conditions (NGC 4636, NGC 4697, and NGC 4374), and our control galaxy, the typical "red and dead" NGC 3379. The current star formation in our closest targets, where we are most complete, is between 2-8 X 10^{-5} Msun/yr. The star formation history was roughly constant from 0.5-1.5 Gyr (at 3-5 X 10^{-4} Msun/yr), but decreased by a factor of several in the past 0.3 Gyr. Most star clusters have a mass between 10^2 - 10^4 Msun. The specific star formation rates of ~10^{-16}/yr (at the present day) or ~10^{-14}/yr (when averaging over the past Gyr) would require timescales 4-6 orders of magnitude longer than the age of the Universe to build up the stellar mass of the galaxies, quantifying for the first time the level of quenching they have experienced relative to their average value. There is no obvious correlation between either the presence or spatial distribution of postulated star formation indicators and the star formation we detect.
Recent infrared observations have demonstrated that photoevaporation driven by high-energy photons from the central star contributes to the dispersal of protoplanetary disks. Here, we show that photoevaporative winds should produce a detectable free-free continuum emission given the range of stellar ionizing photons and X-ray luminosities inferred for young sun-like stars. We point out that VLA observations of the nearby disk around TWHya might have already detected this emission at centimeter wavelengths and calculate the wind electron density and mass flow rate. We also estimate the intensities of H radio recombination lines tracing the wind and discuss which ones could be detected with current instrumentation. The detection and profiles of these recombination lines would unambiguously prove our inference of free-free emission from photoevaporating disks like TWHya. In addition, radio/millimeter data can help constraining wind parameters such as temperature and electron density that are fundamental in measuring mass flow rates.
We have detected a radio bridge of unpolarized synchrotron emission connecting the NW relic of the galaxy cluster Abell 3667 to its central regions. We used data at 2.3 GHz from the S-band Polarization All Sky Survey (S-PASS) and at 3.3 GHz from a follow up observation, both conducted with the Parkes Radio Telescope. This emission is further aligned with a diffuse X-ray bridge, and represents the most compelling direct evidence for an association between intracluster medium turbulence and diffuse synchrotron emission. This is the first clear detection of a bridge associated both with an outlying cluster relic and an X-ray bridge. We conclude that the synchrotron bridge is related to the post-shock turbulence wake trailing a shock front. Although the origin of the relativistic electrons is still unknown, the turbulent re-acceleration model provides a natural explanation for the large-scale emission. The bridge magnetic field intensity is 0.5-0.6 uG. We further detect diffuse emission coincident with the central regions of the cluster for the first time.
Presence of spectral curvature due to synchrotron self-absorption (SSA) of extragalactic radio sources may break down the spectral smoothness feature-the premise that bright radio foreground can be successfully removed in the 21cm experiments of searching for the epoch of reionization (EOR).We present a quantitative estimate of the effect on the measurement of the angular power spectrum of the low-frequency sky,incorporating a phenomenological model,characterized by the fraction of radio sources with turnover frequencies in 100-1000MHz range and a broken power law for the spectral transition around turnover frequencies nu_m,into the simulated radio sources over a small sky area of 10x10 deg^2.We compare statistically the changes in their residual maps with/without inclusion of the SSA after the bright sources of S_150MHz>=100mJy are excised and the best-fitted polynomials in frequency domain on each pixel are further subtracted.It has been shown that the effect of SSA on the detection of EOR depends sensitively on the spectral profiles of radio sources around the turnover frequencies: A hard transition model described by the broken power law with the turnover of spectral index at nu_m would leave pronounced imprints on the residual background and cause serious confusion with the EOR signal.However,the spectral signatures on the angular power spectrum of extragalactic foreground generated by a soft transition model,in which the rise and fall power laws of spectral distribution around nu_m are connected through a smooth transition spanning >=200 MHz in characteristic width,can be fitted and consequently subtracted by employment of polynomials to an acceptable degree(delta T<1mK).As this latter scenario seems to be favored by both theoretical expectation and radio spectral observations,we conclude that the influence of SSA on the 21cm experiments is probably very minor.
The observational progress in the $\gamma$-ray astronomy in the last few
years has led to the discovery of more than a thousand sources at GeV energies
and more than a hundred sources at TeV energies. A few different classes of
compact objects in the Galaxy have been established. They show many unexpected
features at high energies the physics of which remains mainly unknown. At
present it is clear that detailed investigation of these new phenomena can be
performed only with the technical equipment which offer an order of magnitude
better sensitivity, and a few times better energy, angular and time resolution
in the broad energy range staring from a few tens of GeV up to a few hundreds
TeV. Such facilities can be realized by the next generation of instruments such
as the planned Cherenkov Telescope Array (CTA).
The aim of this report is to summarize up to date observational results on
the compact galactic sources in the GeV-TeV $\gamma$-ray energy range, discuss
their theoretical implications, and indicate which hypothesis considered at
present might be verified with the next generation of telescopes. We point out
which of the observational features of the $\gamma$-ray sources are important
to investigate with special care with the planned CTA in order to put a new
light on physical processes involved. Their knowledge should finally allow us
to answer the question on the origin of energetic particles in our Galaxy.
We present the first multi-wavelength follow-up observations of two candidate gravitational-wave (GW) transient events recorded by LIGO and Virgo in their 2009-2010 science run. The events were selected with low latency by the network of GW detectors and their candidate sky locations were observed by the Swift observatory. Image transient detection was used to analyze the collected electromagnetic data, which were found to be consistent with background. Off-line analysis of the GW data alone has also established that the selected GW events show no evidence of an astrophysical origin; one of them is consistent with background and the other one was a test, part of a "blind injection challenge". With this work we demonstrate the feasibility of rapid follow-ups of GW transients and establish the sensitivity improvement joint electromagnetic and GW observations could bring. This is a first step toward an electromagnetic follow-up program in the regime of routine detections with the advanced GW instruments expected within this decade. In that regime multi-wavelength observations will play a significant role in completing the astrophysical identification of GW sources. We present the methods and results from this first combined analysis and discuss its implications in terms of sensitivity for the present and future instruments.
The surface flux transport (SFT) model of solar magnetic fields involves
empirically well-constrained velocity and magnetic fields. The basic evolution
of the Sun's large-scale surface magnetic field is well described by this
model. The azimuthally averaged evolution of the SFT model can be compared to
the surface evolution of the flux transport dynamo (FTD), and the evolution of
the SFT model can be used to constrain several near-surface properties of the
FTD model.
We compared the results of the FTD model with different upper boundary
conditions and diffusivity profiles against the results of the SFT model. Among
the ingredients of the FTD model, downward pumping of magnetic flux, related to
a positive diffusivity gradient, has a significant effect in slowing down the
diffusive radial transport of magnetic flux through the solar surface. Provided
the pumping was strong enough to give rise to a downflow of a magnetic Reynolds
number of 5 in the near-surface boundary layer, the FTD using a vertical
boundary condition matches the SFT model based on the average velocities above
the boundary layer. The FTD model with a potential field were unable to match
the SFT results.
The durations (T_{90}) of 315 Fermi GRBs detected with the GBM-NaI detectors (8-1000 KeV) by 2011 September are calculated using the Bayesian Block method. We compare the T_{90} distribution of the GBM-NaI sample to that observed with CGRO/BATSE (25-2000 keV), BeppoSAX/GRBM (40-700 KeV), HETE-2/FREGATE (6-80 keV), and Swift/BAT (15-150 keV). We show that the T_{90} distribution of the GBM-NaI GRB sample is bimodal, with a statistical significance level being comparable to that observed with BeppoSAX/GRBM and Swift/BAT but much lower than that observed with CGRO/BATSE. No bimodal T_{90} distribution is found in the HETE-2 GRB sample. Taking T_{90}=2 seconds as the division line between long and short GRBs, the ratio of short to long GRB numbers are 0:95, 51:557, 111:892, 39:253, and 500:1541 for the HETE-2/FREGATE, Swift/BAT, BeppoSAX/GRBM, GBM-NaI, and CGRO/BATSE GRB samples, respectively. These results suggest that the bimodal T_{90} distribution would be due to an instrumental selection effect. We investigate the energy dependence of T_{90} by measuring the T_{90} in the 8-15 KeV, 15-25 keV, 25-20 KeV, 50-100 keV, 100-350 keV, and 350-1000 keV energy bands with the GBM-NaI data. It is found that the T_{90} distributions in different energy bands are roughly consistent with the those derived from the instruments with similar corresponding energy bands. The value of T_{90} as a function of energy follows a relation T_{90}~ E^{-0.15}. Including X-ray flares, we found that the central engine activity time scale can be even much longer for some GRBs. Our results, together with the observed extended emission of Type I GRBs and significant flares in both the Type I and Type II GRBs, not only challenges the long-short GRB classification scheme, but also challenges the conventional GRB central engine models.
The Galaxy hosts a widespread population of low-energy positrons revealed by successive generations of gamma-ray telescopes through a bright annihilation emission from the bulge region, with a fainter contribution from the inner disk. The exact origin of these particles remains currently unknown. We estimate the contribution to the annihilation signal of positrons generated in the decay of radioactive 26Al, 56Ni and 44Ti. We adapted the GALPROP propagation code to simulate the transport and annihilation of radioactivity positrons in a model of our Galaxy. Using plausible source spatial distributions, we explored several possible propagation scenarios to account for the large uncertainties on the transport of ~1MeV positrons in the interstellar medium. We then compared the predicted intensity distributions to the INTEGRAL/SPI observations. We obtain similar intensity distributions with small bulge-to-disk ratios, even for extreme large-scale transport prescriptions. At least half of the positrons annihilate close to their sources, even when they are allowed to travel far away. In the high-diffusion, ballistic case, up to 40% of them escape the Galaxy. In proportion, this affects bulge positrons more than disk positrons because they are injected further off the plane in a tenuous medium, while disk positrons are mostly injected in the dense molecular ring. The predicted intensity distributions are fully consistent with the observed longitudinally-extended disk-like emission, but the transport scenario cannot be strongly constrained by the current data. Nucleosynthesis positrons alone cannot account for the observed annihilation emission in the frame of our model. An additional component is needed to explain the strong bulge contribution, and the latter is very likely concentrated in the central regions if positrons have initial energies in the 100keV-1MeV range.
We review the difficulties of the generalized Chaplygin gas model to fit observational data, due to the tension between background and perturbative tests. We argue that such issues may be circumvented by means of a self-interacting scalar field representation of the model. However, this proposal seems to be successful only if the self-interacting scalar field has a non-canonical form. The latter can be implemented in Rastall's theory of gravity, which is based on a modification of the usual matter conservation law. We show that, besides its application to the generalized Chaplygin gas model, other cosmological models based on Rastall's theory have many interesting and unexpected new features.
The HI 21cm absorption optical depth and the N(HI) derived from Lya absorption can be combined to yield the spin temperature (Ts) of DLAs. Although Ts measurements exist for samples of DLAs with z <0.6 and z >1.7, the intermediate redshift regime currently contains only 2 HI 21cm detections, leading to a `redshift desert' that spans 4 Gyrs of cosmic time. To connect the low and high z regimes, we present observations of the Lya line of six 0.6<z<1.7 HI 21cm absorbers. The dataset is complemented by both VLBA observations (to derive the absorber covering factor, f), and optical echelle spectra from which metal abundances are determined. Our dataset therefore not only offers the largest statistical study of HI 21cm absorbers to date, and bridges the redshift desert, but is also the first to use a fully f-corrected dataset to look for metallicity-based trends. In agreement with trends found in Galactic sightlines, we find that the lowest N(HI) absorbers tend to be dominated by warm gas. In the DLA regime, spin temperatures show a wider range of values than Galactic data, as may be expected in a heterogenous galactic population. However, we find that low metallicity DLAs are dominated by small cold gas fractions and only absorbers with relatively high metallicities exhibit significant fractions of cold gas. Using a compilation of HI 21cm absorbers which are selected to have f-corrected spin temperatures, we confirm an anti-correlation between metallicity and Ts at 3.4 sigma significance. Finally, one of the DLAs in our sample is a newly-discovered HI 21cm absorber (at z=0.602 towards J1431+3952), which we find to have the lowest f-corrected spin temperature yet reported in the literature: Ts=90+-23 K. The observed distribution of Ts and metallicities in DLAs and the implications for understanding the characteristics of the interstellar medium in high redshift galaxies are discussed.
We consider the influence of decaying dark matter (DM) particles on the characteristics of 21 cm absorption in spectra of distant radio-loud sources - "21 cm forest" - from minihaloes with masses $M=10^5-10^7\msun$ virialized at $z_{vir} = 10$. We use 1D self-consistent hydrodynamic description to study evolution of minihaloes, and follow up their absorption characteristics from turnaround to virialization. We find that in the presence of decaying dark matter both thermal and dynamical evolution of minihaloes demonstrate significant deviation from those in the model without dark matter decay (standard recombination). We show that optical depth in 21 cm line is strongly suppressed in the presence of decaying particles: for $M=10^5-10^6\msun$ decaying dark matter with the energy rate deposited in baryonic gas $\xi_{L} = 0.59\times 10^{-25}$ s$^{-1}$ - the current upper limit of the energy deposit - decreases the optical depth and the equivalent width by an order of magnitude compared to the standard recombination. Thus additional ionization and heating from decaying DM particles almost "erases" absorption features from minihaloes with $M=10^5-10^6\msun$ for $\xi \simgt 0.3\xi_L$, which consequently considerably decreases the number of strong absorptions: for example, the number of absorptions with the equivalent width $W_\nu^{obs} \simgt 0.3$ kHz at $z\simeq10$ decreases more than 2.5 times for $\xi/\xi_{L} = 0.3$ and $\simgt$4.5 times for $\xi/\xi_{L} = 1$. We argue that "21 cm forest" absorptions might be a powerful probe of the presence of decaying dark matter in the early Universe.
Aims: The determination of elusive redshifts of bright BL Lac objects Methods: We use the capabilities of newly available spectrograph X-Shooter at European Southern Observatory (ESO) Very Large Telescope, that combines high resolution and a large wavelength range, to obtain UVB to near-IR spectra of BL Lacs. Results: Our observations of PKS 0048-097 detect three emission lines that permit to derive a redshift z = 0.635. Moreover, a Mg II absorption system at z = 0.154 that is associated with a foreground spiral galaxy at 50 Kpc projected distance is found. Conclusions: The obtained redshift allows us to comment about the optical beaming factor and the absorption of the high energy spectrum by the Extragalactic Background Light.
Currently used model of spherical accretion onto a magnetized rotating neutron star encounters major difficulties in explaining the entry rate of accreting material into the stellar field and spin evolution of long-period X-ray pulsars. These difficulties can be, however, avoided if the magnetic field of the material captured by the neutron star is incorporated into the model. The magnetic field of the flow itself under certain conditions controls the accretion process and significantly affects the parameters of the accreting material. The mode by which the accretion flow enters the stellar magnetosphere in that case can be associated with Bohm (or turbulent) diffusion and the torque applied to the neutron star appears to be substantially higher than that evaluated in the non-magnetized accretion scenario.
We describe the use of Graphics Processing Units (GPUs) for speeding up the code NBODY6 which is widely used for direct $N$-body simulations. Over the years, the $N^2$ nature of the direct force calculation has proved a barrier for extending the particle number. Following an early introduction of force polynomials and individual time-steps, the calculation cost was first reduced by the introduction of a neighbour scheme. After a decade of GRAPE computers which speeded up the force calculation further, we are now in the era of GPUs where relatively small hardware systems are highly cost-effective. A significant gain in efficiency is achieved by employing the GPU to obtain the so-called regular force which typically involves some 99 percent of the particles, while the remaining local forces are evaluated on the host. However, the latter operation is performed up to 20 times more frequently and may still account for a significant cost. This effort is reduced by parallel SSE/AVX procedures where each interaction term is calculated using mainly single precision. We also discuss further strategies connected with coordinate and velocity prediction required by the integration scheme. This leaves hard binaries and multiple close encounters which are treated by several regularization methods. The present nbody6-GPU code is well balanced for simulations in the particle range $10^4-2 \times 10^5$ for a dual GPU system attached to a standard PC.
Dwarf galaxies (DGs) are extremely challenging objects in extragalactic astrophysics. They are expected to originate as the first units in Cold Dark-Matter cosmology. They are the galaxy type most sensitive to environmental influences and their division into multiple types with various properties have invoked the picture of their variant morphological transformations. Detailed observations reveal characteristics which allow to deduce the evolutionary paths and to witness how the environment has affected the evolution. Here we review peculiarities of general morphological DG types and refer to processes which can deplete gas-rich irregular DGs leading to dwarf ellipticals, while gas replenishment implies an evolutionary cycling. Finally, as the less understood DG types the Milky Way satellite dwarf spheroidal galaxies are discussed in the context of transformation.
Long baseline laser interferometers used for gravitational wave detection have proven to be very complicated to control. In order to have sufficient sensitivity to astrophysical gravitational waves, a set of multiple coupled optical cavities comprising the interferometer must be brought into resonance with the laser field. A set of multi-input, multi-output servos then lock these cavities into place via feedback control. This procedure, known as lock acquisition, has proven to be a vexing problem and has reduced greatly the reliability and duty factor of the past generation of laser interferometers. In this article, we describe a technique for bringing the interferometer from an uncontrolled state into resonance by using harmonically related external fields to provide a deterministic hierarchical control. This technique reduces the effect of the external seismic disturbances by four orders of magnitude and promises to greatly enhance the stability and reliability of the current generation of gravitational wave detector. The possibility for using multi-color techniques to overcome current quantum and thermal noise limits is also discussed.
We present a study of new Australian Telescope Compact Array (ATCA) observations of supernova remnant, SNR J0536-6735. This remnant appears to follow a shell morphology with a diameter of D=36x29 pc (with 1 pc uncertainty in each direction). There is an embedded Hii region on the northern limb of the remnant which made various analysis and measurements (such as flux density, spectral index and polarisation) difficult. The radio-continuum emission followed the same structure as the optical emission, allowing for extent and flux density estimates at 20 cm. We estimate a surface brightness for the SNR at 1 GHz of 2.55x10^-21 W m^-2 Hz^-1 sr^-1. Also, we detect a distinctive radio-continuum point source which confirms the previous suggestion of this remnant being associated with a pulsar wind nebulae (PWN). The tail of this remnant isn't seen in the radio-continuum images and is only seen in the optical and X-ray images.
We present an analytic calculation of the gravitational field inside and near a caustic ring of dark matter. The calculation may facilitate N-body simulation studies on the effects that dark matter caustics have on galaxy formation.
The characteristics of light variation of RSGs in SMC are analyzed based on the nearly 8-10 year long data collected by the ASAS and MACHO projects. The identified 126 RSGs are classified into five categories accordingly: 20 with poor photometry, 55 with no reliable period, 6 with semi-regular variation, 15 with Long Secondary Period (LSP) and distinguishable short period and 30 with only LSP. For the semi-regular variables and the LSP variables with distinguishable short period, the Ks band period-luminosity (P-L) relation is analyzed and compared with that of the Galaxy, LMC and M33. It is found that the RSGs in these galaxies obey similar P-L relation except the Galaxy. In addition, the P-L relations in the infrared bands, namely the 2MASS JHKs, Spitzer/IRAC and Spitzer/MIPS 24 {\mu}m bands, are derived with high reliability. The best P-L relation occurs in the Spitzer/IRAC [3.6] and [4.5] bands. Based on the comparison with the theoretical calculation of the P-L relation, the mode of pulsation of RSGs in SMC is suggested to be the first overtone radial mode.
This work is a continuation of two previous papers of a series, in which we examined the pulse-width statistics of normal radio pulsars. In the first paper we compiled the largest ever database of pulsars with interpulses in their mean profiles. In the second one we confirmed the existence of the lower boundary in the scatter plot of core component pulse-widths versus pulsar period W50 sim 2.5 P^{-0.5}[deg], first discovered by Rankin using much smaller number of interpulse cases. In this paper we show that the same lower boundary also exists for conal profile components. Rankin proposed a very simple method of estimation of pulsar inclination angle based on comparing the width W50 of its core component with the period dependent value of the lower boundary. We claim that this method can be extended to conal components as well. To explain an existence of the lower boundary Rankin proposed that the core emission originates at or near the polar cap surface. We demonstrated clearly that no coherent pulsar radio emission can originate at altitudes lower than 10 stellar radii, irrespective of the actual mechanism of coherence. We argue that the lower boundary reflects the narrowest angular structures that can be distinguished in the average pulsar beam. These structures represent the core and the conal components in mean pulsar profiles. The P^{-0.5} dependence follows from the dipolar nature of magnetic field lines in the radio emission region, while the numerical factor of about 2.5 deg reflects the curvature radius of a non-dipolar surface magnetic field in the partially screened gap above the polar cap, where dense electron-positron plasma is created. Both core and conal emission should originate at altitudes of about 50 stellar radii in a typical pulsar, with a possibility that the core beam is emitted at a slightly lower heights than the conal ones.
We use the wide-field capabilities of the 2dF fibre positioner and the AAOmega spectrograph on the Anglo-Australian Telescope (AAT) to obtain redshifts of galaxies that hosted supernovae during the first three years of the Supernova Legacy Survey (SNLS). With exposure times ranging from 10 to 60 ksec per galaxy, we were able to obtain redshifts for 400 host galaxies in two SNLS fields, thereby substantially increasing the total number of SNLS supernovae with host galaxy redshifts. The median redshift of the galaxies in our sample that hosted photometrically classified Type Ia supernovae (SNe Ia) is 0.77, which is 25% higher than the median redshift of spectroscopically confirmed SNe Ia in the three-year sample of the SNLS. Our results demonstrate that one can use wide-field fibre-fed multi-object spectrographs on 4m telescopes to efficiently obtain redshifts for large numbers of supernova host galaxies over the large areas of sky that will be covered by future high-redshift supernova surveys, such as the Dark Energy Survey.
The gravitational fields of two isolated ellipticals, NGC 720 and NGC 1521, have been recently measured, assuming hydrostatic balance of the hot gas enshrouding them. These galaxies are worthy of special interest: They afford, for the first time to my knowledge, testing MOND in ellipticals with force and quality that, arguably, approach those of rotation-curve tests in disc galaxies: The fields have been probed to very large galactic radii, revealing a large range of mass discrepancies. In the context of MOND, it is noteworthy that the measured accelerations span a wide range, from more than 10a0 to about a0/10, unprecedented in individual ellipticals. I compare the predictions of MOND, based on only the baryonic mass, for reasonable stellar M/L values, with the deduced dynamical mass runs of these galaxies. I find that MOND predicts correctly the runs of the mass discrepancies: from no discrepancy in the inner parts, to approximately a-factor-of-ten discrepancy in the outermost regions probed. For NGC 1521, this is achieved with the same M/L value as best fitted the data in the Newtonian analysis with dark matter, and for NGC 720, with a somewhat larger value than preferred by the Newtonian fit.
I discuss a novel MOND effect that entails a small correction to the dynamics of isolated mass systems even when they are deep in the Newtonian regime. [These are systems whose extent R<< Rm, where Rm=sqrt(GM/a0) is the MOND radius of the system, of total mass M.] Interestingly, even if the MOND equations approach Newtonian dynamics arbitrarily fast at high accelerations, this correction decreases only as a power of R/Rm. The effect appears in formulations of MOND as modified gravity governed by generalizations of the Poisson equation. The MOND correction to the potential is a quadrupole field \phi_{a} \approx GP_{ij}r^ir^j, where r is the radius from the center of mass. In QUMOND, P_{ij}=-q Q_{ij}/Rm^5, where Q_{ij} is the quadrupole moment of the system, and q>0 is a numerical factor that depends on the interpolating function. For example, the correction to the Newtonian force between two masses, m and M, a distance L apart (L<<Rm) is Fa=2q(L/Rm)^3(mM)^2(M+m)^{-3}a0 (attractive). At present I don't see where this effect can be tested. For example, it's predicted strength is rather much below present testing capabilities in the solar system, for which the added acceleration is of order 10^{-12}a0. (Abridged)
Images from the SWAP (Proba 2 mission) taken at 174A in the Fe IX/X lines are compared to simultaneous slitless flash spectra taken during the last solar total eclipse of July, 11th 2010. Many faint low excitation emission lines together with the HeI and HeII Paschen Alpha chromospheric lines are recorded on eclipse spectra where regions of limb prominences are obtained with space-borne imagers. We consider a deep flash spectrum obtained by summing 80 individual spectra to show the intensity modulations of the continuum. Intensity depressions are observed around the prominences in both eclipse and SWAP images. The prominence cavities are interpreted as a relative depression of plasma density, produced inside the corona surrounding the prominences. Photometric measurements are shown at different scales and different, spectrally narrow, intervals for both the prominences and the coronal background.
We have derived a new expression for the thermohaline mixing coefficient in stars, including the effects of radiative levitation and external turbulence, by solving Boussinesq equations in a quasi-incompressible fluid with a linear approximation. It is well known that radiative levitation of individual elements can lead to their accumulation in specific stellar layers. In some cases, it can induce important effects on the stellar structure. Here we confirm that this accumulation is moderated by thermohaline convection due to the resulting inverse $\mu$-gradient. The new coefficient that we have derived shows that the effect of radiative accelerations on the thermohaline instability itself is small. This effect must however be checked in all computations. We also confirm that the presence of large horizontal turbulence can reduce or even suppress the thermohaline convection. These results are important as they concern all the cases of heavy element accumulation in stars. The computations of radiative diffusion have to be revisited including thermohaline convection and its consequences. It may be one of the basic reasons for the fact that the observed abundances are always smaller than those predicted by pure atomic diffusion. In any case, these processes have to compete with rotation-induced mixing, but this competition is more complex than previously thought due to their mutual interaction.
The low metallicity interstellar medium of dwarf galaxies gives a different
picture in the far infrared(FIR)/submillimetre(submm)wavelengths than the more
metal-rich galaxies. Excess emission is often found in the submm beginning at
or beyond 500 mu. Even without taking this excess emission into account as a
possible dust component, higher dust-to-gas mass ratios (DGR) are often
observed compared to that expected from their metallicity for moderately
metal-poor galaxies.
The SEDs of the lowest metallicity galaxies, however, give very low dust
masses and excessively low values of DGR, inconsistent with the amount of
metals expected to be captured into dust if we presume the usual linear
relationship holding for all metallicities, including the more metal-rich
galaxies. This transition seems to appear near metalllicities of 12 + log(O/H)
~ 8.0 - 8.2. These results rely on accurately quantifying the total molecular
gas reservoir, which is uncertain in low metallicity galaxies due to the
difficulty in detecting CO(1-0) emission. Dwarf galaxies show an exceptionally
high [CII] 158 mu/CO (1-0) ratio which may be indicative of a significant
reservoir of 'CO-free' molecular gas residing in the photodissociated envelope,
and not traced by the small CO cores.
We investigate the orbital stability of a putative Jovian planet reported by Ramm et. al in a compact binary \nu Octantis. Our numerical study makes use of a new computational Message Passing Interface (MPI) framework Mechanic which we developed to run massive numerical experiments on CPU clusters. The code is illustrated on a model Hamiltonian introduced by Froeschl\'e et al. We confirm that the \nu Octantis planet could reside in a retrograde orbit, according with a hypothesis of Eberle & Cuntz. It may be present in a zone of stable motions which has a structure of the Arnold web formed due to overlapping of low-order mean motion resonances and their sub-resonances. We also re-analyzed the available radial velocity data in terms of self-consistent Newtonian N-body model. We found stable best-fit solutions that obey the observational constraints. They correspond to retrograde, strictly anti-aligned orbits of the binary and the planet. However, these solutions are confined in very small stable regions of the phase space. The presence of a real planet in the system is still questionable, because its formation would be hindered by strong dynamical perturbations.
Rapid and strong changes in the Blazhko modulation of RR Lyrae stars, as they have recently been detected in high precision satellite data, have become a crucial topic in finding an explanation of the long-standing mystery of the Blazhko effect. We present here an analysis of the most extreme case detected so far, the RRab star V445 Lyr (KIC 6186029) which was observed with the Kepler space mission. V445 Lyr shows very strong cycle-to-cycle changes in its Blazhko modulation, which are caused both by a secondary long-term modulation period as well as irregular variations. In addition to the complex Blazhko modulation, V445 Lyr also shows a rich spectrum of additional peaks in the frequency range between the fundamental pulsation and the first harmonic. Among those peaks, the second radial overtone could be identified, which, combined with a metallicity estimate of [Fe/H]=-2.0 dex from spectroscopy, allowed to constrain the mass (0.55-0.65 M_sun) and luminosity (40-50 L_sun) of V445 Lyr through theoretical Petersen diagrams. A non-radial mode as well as possibly the first overtone are also excited. Furthermore, V445 Lyr shows signs of the period doubling phenomenon and a long term period change. A detailed Fourier analysis along with a study of the O-C variation of V445 Lyr is presented, and the origin of the additional peaks and possible causes of the changes in the Blazhko modulation are discussed. The results are then put into context with those of the only other star with a variable Blazhko effect for which a long enough set of high precision continuous satellite data has been published so far, the CoRoT star 105288363.
We study the far-infrared emission from the nearby spiral galaxy M33 in order to investigate the dust physical properties such as the temperature and the luminosity density across the galaxy. Taking advantage of the unique wavelength coverage (100, 160, 250, 350 and 500 micron) of the Herschel Space Observatory and complementing our dataset with Spitzer-IRAC 5.8 and 8 micron and Spitzer-MIPS 24 and 70 micron data, we construct temperature and luminosity density maps by fitting two modified blackbodies of a fixed emissivity index of 1.5. We find that the 'cool' dust grains are heated at temperatures between 11 and 28 K with the lowest temperatures found in the outskirts of the galaxy and the highest ones in the center and in the bright HII regions. The infrared/submillimeter total luminosity (5 - 1000 micron) is estimated to be 1.9x10^9 Lsun. 59% of the total luminosity of the galaxy is produced by the 'cool' dust grains (~15 K) while the rest 41% is produced by 'warm' dust grains (~55 K). The ratio of the cool-to-warm dust luminosity is close to unity (within the computed uncertainties), throughout the galaxy, with the luminosity of the cool dust being slightly enhanced in the center of the galaxy. Decomposing the emission of the dust into two components (one emitted by the diffuse disk of the galaxy and one emitted by the spiral arms) we find that the fraction of the emission in the disk in the mid-infrared (24 micron) is 21%, while it gradually rises up to 57% in the submillimeter (500 micron). We find that the bulk of the luminosity comes from the spiral arm network that produces 70% of the total luminosity of the galaxy with the rest coming from the diffuse dust disk. The 'cool' dust inside the disk is heated at a narrow range of temperatures between 18 and 15 K (going from the center to the outer parts of the galaxy).
Only a small number of high mass stars (> 30 Mo) have fundamental parameters measured with high enough accuracy from eclipsing binaries to constrain formation and evolutionary models of massive stars. This work aims to increase this limited sample, by studying the 4 massive eclipsing binary candidates discovered by Bonanos in the young massive cluster Westerlund 1. We present new follow-up echelle spectroscopy of these binaries and models of their light and radial velocity curves. We obtain fundamental parameters (i.e. masses, radii) for the 8 component stars, finding masses that span a range of 10-40 Mo, and contributing accurate fundamental parameters for 1 additional very massive star, the 33 Mo component of W13. WR77o is found to have a ~40 Mo companion, which provides a second dynamical constraint on the mass of the progenitor of the magnetar known in the cluster. We also use W13 to estimate the first, direct, eclipsing binary distance to Westerlund 1 and therefore the magnetar, and find it to be at 4.0 +/- 0.6 kpc. Our results confirm previous evidence for a high mass for the progenitor of the magnetar. In addition, the availability of eclipsing binaries with accurate parameters opens the way for direct, independent, high precision eclipsing binary distance measurements to Westerlund 1.
The Very Long Baseline Interferometry (VLBI) monitoring program TANAMI provides bi-monthly, dualfrequency (8GHz and 22GHz) observations of extragalactic jets with milliarcsecond resolution south of -30 deg declination using the Australian Long Baseline Array (LBA) and additional radio telescopes in Antarctica, Chile, New Zealand and South Africa. Supporting programs provide multiwavelength coverage of the Fermi/LAT sources of the TANAMI sample, in order to construct simultaneous broadband spectral energy distributions (SEDs), as well as rapid follow-ups of high energy flares. The main purpose of this project is to study the radio-gamma-ray connection seen in the jets of active galactic nuclei (AGN) via simultaneous monitoring of their VLBI structure and broadband emission in order to distinguish between different proposed emission models. Here we give a brief description of the TANAMI program and will then focus on its current status: (1) We present some results on the first simultaneous dual-frequency images of the whole sample resulting in spectral index maps of the parsec-scale core-jet structure. (2) The TANAMI array allows us to observe the closest radio galaxy Centaurus A with unprecedented high angular resolution resulting in the best-ever image of an AGN jet. We constructed the best resolved spectral index map of its jet-counterjet system revealing multiple possible production sites of gamma-rays recently detected by Fermi/LAT. With the first epochs of the TANAMI monitoring, we can study the proper jet motion of individual jet components of Cen A on sub-parsec scales. (3) Since the launch of Fermi/LAT we added newly detected gamma-ray bright AGN to the TANAMI observing list which is built as a combined radio and gamma-ray selected sample. For most of these sources the TANAMI observations obtain the first VLBI images ever made.
An analytic expression for the variation in surface and sub-surface temperature is developed for worlds whose surface pressures are nearly constant with latitude and longitude and whose atmospheres are in vapor-pressure equilibrium with the dominant surface volatiles. Such worlds include the current Pluto and Triton, and other volatile-covered Kuiper Belt Objects during some portion of their heliocentric orbit. The expressions also apply on worlds with negligible horizontal heat flow, such as asteroids. Temperature variations in volatile-covered or bare areas as a function of time is derived in terms of three thermal parameters relating to (1) the thermal wave within the substrate, (2) the energy needed to heat an isothermal volatile slab, and (3) the buffering by the latent heat needed to change the atmospheric surface pressure. For Pluto's current surface pressure (~17 microbar), atmospheric buffering dominates over subsurface effects on diurnal timescales, and should keep the surface pressure over a Pluto day constant to within 0.2%.
By taking into account the local energy balance per unit volume between the viscous heating and the advective cooling plus the radiative cooling, we investigate the vertical structure of radiation pressure-supported accretion disks in spherical coordinates. Our solutions show that the photosphere of the disk is close to the polar axis and therefore the disk seems to be extremely thick. However, the profile of density implies that most of the accreted matter exists in a moderate range around the equatorial plane. We show that the well-known polytropic relation between the pressure and the density is unsuitable for describing the vertical structure of radiation pressure-supported disks. More importantly, we find that the energy advection is significant even for slightly sub-Eddington accretion disks. We argue that the non-negligible advection may help to understand why the standard thin disk model is likely to be inaccurate above \sim 0.3 Eddington luminosity, which was found by some works on the black hole spin measurement. Furthermore, the solutions satisfy the Solberg-Hoiland conditions, which indicates the disk to be convectively stable. In addition, we discuss the possible link between our disk model and ultraluminous X-ray sources.
We present a method to optimize absorption cells for precise wavelength calibration in the near-infrared. We apply it to design and optimize methane isotopologue cells for precision radial velocity measurements in the K band. We also describe the construction and installation of two such cells for the CSHELL spectrograph at NASA's IRTF. We have obtained their high-resolution laboratory spectra, which we can then use in precision radial velocity measurements and which can also have other applications. In terms of obtainable RV precision methane should out-perform other proposed cells, such as the ammonia cell ($^{14}$NH$_{3}$) recently demonstrated on CRIRES/VLT. The laboratory spectra of Ammonia and the Methane cells show strong absorption features in the H band that could also be exploited for precision Doppler measurements. We present spectra and preliminary radial velocity measurements obtained during our first-light run. These initial results show that a precision down to 20-30 m s$^{-1}$ can be obtained using a wavelength interval of only 5 nm in the K band and S/N$\sim$150. This supports the prediction that a precision down to a few m s$^{-1}$ can be achieved on late M dwarfs using the new generation of NIR spectrographs, thus enabling the detection of terrestrial planets in their habitable zones. Doppler measurements in the NIR can also be used to mitigate the radial velocity jitter due to stellar activity enabling more efficient surveys on young active stars.
Reverberation mapping offers one of the best techniques for studying the
inner regions of QSOs. It is based on cross-correlating continuum and
emission-line light curves. New time-resolved optical surveys will produce well
sampled light curves for many thousands of QSOs. We explore the potential of
stacking samples to produce composite cross-correlations for groups of objects
that have well sampled continuum light curves, but only a few (~2)
emission-line measurements. This technique exploits current and future
wide-field optical monitoring surveys (e.g. Pan-STARRS, LSST) and the
multiplexing capability of multi-object spectrographs (e.g. 2dF, Hectospec) to
significantly reduce the observational expense of reverberation mapping, in
particular at high redshift (0.5 to 2.5).
We demonstrate the technique using simulated QSO light curves and explore the
biases involved when stacking cross-correlations in some simplified situations.
We show that stacked cross correlations have smaller amplitude peaks compared
to well sampled correlation functions as the mean flux of the emission light
curve is poorly constrained. However, the position of the peak remains intact.
We find there can be `kinks' in stacked correlation functions due to different
measurements contributing to different parts of the correlation function.
Using the Pan-STARRS Medium-Deep Survey (MDS) as a template we show that
cross-correlation lags should be measurable in a sample size of 500 QSOs that
have weekly photometric monitoring and two spectroscopic observations. Finally
we apply the technique to a small sample (42) of QSOs that have light curves
from the MDS. We find no indication of a peak in the stacked cross-correlation.
A larger spectroscopic sample is required to produce robust reverberation lags.
We rise in this Letter the possibility that the very dense, compact companion of PSR J1719-1438, having a Jupiter-like mass is an exotic quark object rather than a light helium or carbon white dwarf. The exotic hypothesis explains naturally some of the observed features, and gives quite strong predictions for this system, to be confirmed or refuted in future feasible studies.
Our aim is to assess the benefits and limitations of using the redundant
visibility information in regular phased array systems for improving the
calibration.
Regular arrays offer the possibility to use redundant visibility information
to constrain the calibration of the array independent of a sky model and a beam
models of the station elements. It requires a regular arrangement in the
configuration of array elements and identical beam patterns.
We revised a calibration method for phased array stations using the redundant
visibility information in the system and applied it successfully to a LOFAR
station. The performance and limitations of the method were demonstrated by
comparing its use on real and simulated data. The main limitation is the mutual
coupling between the station elements, which leads to non-identical beams and
stronger baseline dependent noise. Comparing the variance of the estimated
complex gains with the Cramer-Rao Bound (CRB) indicates that redundancy is a
stable and optimum method for calibrating the complex gains of the system.
Our study shows that the use of the redundant visibility does improve the
quality of the calibration in phased array systems. In addition it provides a
powerful tool for system diagnostics. Our results demonstrate that designing
redundancy in both the station layout and the array configuration of future
aperture arrays is strongly recommended. In particular in the case of the
Square Kilometre Array with its dynamic range requirement which surpasses any
existing array by an order of magnitude.
High rate sampling detectors measuring the potential difference between the main body and boom antennas of interplanetary spacecraft have been shown to be efficient means to measure the voltage pulses induced by nano dust impacts on the spacecraft body itself (see Meyer-Vernet et al, Solar Phys. 256, 463 (2009)). However, rough estimates of the free charge liberated in post impact expanding plasma cloud indicate that the cloud's own internal electrostatic field is too weak to account for measured pulses as the ones from the TDS instrument on the STEREO spacecraft frequently exceeding 0.1 V/m$. In this paper we argue that the detected pulses are not a direct measure of the potential structure of the plasma cloud, but are rather the consequence of a transitional interruption of the photoelectron return current towards the portion of the antenna located within the expanding cloud.
Events like inflation or phase transitions can produce large density perturbations on very small scales in the early Universe. Probes of small scales are therefore useful for e.g. discriminating between inflationary models. Until recently, the only such constraint came from non-observation of primordial black holes (PBHs), associated with the largest perturbations. Moderate-amplitude perturbations can collapse shortly after matter-radiation equality to form ultracompact minihalos (UCMHs) of dark matter, in far greater abundance than PBHs. If dark matter self-annihilates, UCMHs become excellent targets for indirect detection. Here we discuss the gamma-ray fluxes expected from UCMHs, the prospects of observing them with gamma-ray telescopes, and limits upon the primordial power spectrum derived from their non-observation by the Fermi Large Area Space Telescope.
Young star clusters like R136 in the Large Magellanic Cloud and NGC 3603, Westerlund 1, and 2 in the Milky Way are dynamically more evolved than expected based on their current relaxation times. In particular, the combination of a high degree of mass segregation, a relatively low central density, and the large number of massive runaway stars in their vicinity are hard to explain with the monolithic formation of these clusters. Young star clusters can achieve such a mature dynamical state if they formed through the mergers of a number of less massive clusters. The shorter relaxation times of less massive clusters cause them to dynamically evolve further by the time they merge, and the merger product preserves the memory of the dynamical evolution of its constituent clusters. With a series of $N$-body simulations, we study the dynamical evolution of single massive clusters and those that are assembled through merging smaller clusters together. We find that the formation of massive star clusters through the mergers of smaller clusters can reproduce the currently observed spatial distribution of massive stars, the density, and the characteristics (number and mass distribution) of the stars ejected as runaways from young dense clusters. We therefore conclude that these clusters and possibly other young massive star clusters formed through the mergers of smaller clusters.
Context. Outflows and jets are the first signposts of ongoing star formation processes in any molecular cloud, yet their study in optical bands provides limited results due to the large extinction present. Near-infrared unbiased wide-field observations in the H2 1-0 S(1) line at 2.122{\mu}m alleviates the problem, enabling us to detect more outflows and trace them closer to their driving sources. Aims. As part of a large-scale multi-waveband study of ongoing star formation in the Braid Nebula Star Formation region, we focus on a one square degree region that includes Lynds Dark Nebula 1003 and 1004. Our goal is to find all of the near-infrared outflows, uncover their driving sources and estimate their evolutionary phase. Methods. We use near-infrared wide-field observations obtained with WFCAM on UKIRT, in conjunction with previously-published optical and archival MM data, to search for outflows and identify their driving sources; we subsequently use colour-colour analysis to determine the evolutionary phase of each source. Results. Within a one square degree field we have identified 37 complex MHOs, most of which are new. After combining our findings with other wide-field, multi-waveband observations of the same region we were able to discern 28 outflows and at least 18 protostars. Our analysis suggests that these protostars are younger and/or more energetic than those of the Taurus-Auriga region. The outflow data enable us to suggest connection between outflow ejection and repetitive FU Ori outburst events. We also find that star formation progresses from W to E across the investigated region.
(abridged) We report the results of a 10-year timing campaign on PSR J1738+0333, a 5.85-ms pulsar in a low-eccentricity 8.5-hour orbit with a low-mass white dwarf companion (...) The measurements of proper motion and parallax allow for a precise subtraction of the kinematic contribution to the observed orbital decay; this results in a significant measurement of the intrinsic orbital decay: (-25.9 +/- 3.2) \times 10^{-15} s/s. This is consistent with the orbital decay from the emission of gravitational waves predicted by general relativity, (-27.7 +1.5/-1.9) \times 10^{-15} s/s (...). This agreement introduces a tight upper limit on dipolar gravitational wave emission, a prediction of most alternative theories of gravity for asymmetric binary systems such as this. We use this limit to derive the most stringent constraints ever on a wide class of gravity theories, where gravity involves a scalar field contribution. When considering general scalar-tensor theories of gravity, our new bounds are more stringent than the best current solar-system limits over most of the parameter space, and constrain the matter-scalar coupling constant {\alpha}_0^2 to be below the 10^{-5} level. For the special case of the Jordan-Fierz-Brans-Dicke, we obtain the one-sigma bound {\alpha}_0^2 < 2 \times 10^{-5}, which is within a factor two of the Cassini limit. We also use our limit on dipolar gravitational wave emission to constrain a wide class of theories of gravity which are based on a generalization of Bekenstein's Tensor-Vector-Scalar gravity (TeVeS), a relativistic formulation of Modified Newtonian Dynamics (MOND).
The Cherenkov Telescope Array (CTA), currently in its Preparatory Phase, will
be the first open observatory for very high energy gamma-rays from galactic and
extragalactic sources. The international consortium behind CTA is preparing the
construction of two large arrays of Cherenkov telescopes in the Northern and
Southern Hemispheres with a performance that will be significantly improved
compared to the current generation of arrays.
Its increased sensitivity and energy range will give CTA access to a large
population of Active Galactic Nuclei (AGN) not yet detected at very high
energies and provide much more details on known TeV sources. While the low end
of the CTA energy coverage will close the current gap with the Fermi-LAT band,
its high energy coverage will open a new window on the sky and help us
understand the intrinsic shape of the hardest blazar spectra.
We outline the current status of CTA and discuss the science case for AGN
physics with the observatory. Predictions for source detections based on
extrapolations of Fermi-LAT spectra are discussed. An overview is given of
prospects for the detection of extended emission from radio galaxies, of rapid
variability, and spectral features. The observation of AGN with CTA will also
improve current constraints on the distribution of the extragalactic background
light, the strength of the intergalactic magnetic field and Lorentz invariance
violation.
(ABRIDGED) We present here the results from new Very Long Baseline Array observations at 1.6 and 5 GHz of 19 galaxies of a complete sample of 21 UGC FRI radio galaxies. New Chandra data of two sources, viz., UGC00408 and UGC08433, are combined with the Chandra archival data of 13 sources. The 5 GHz observations of ten "core-jet" sources are polarization-sensitive, while the 1.6 GHz observations constitute second epoch total intensity observations of nine "core-only" sources. Polarized emission is detected in the jets of seven sources at 5 GHz, but the cores are essentially unpolarized, except in M87. Polarization is detected at the jet edges in several sources, and the inferred magnetic field is primarily aligned with the jet direction. This could be indicative of magnetic field "shearing" due to jet-medium interaction, or the presence of helical magnetic fields. The jet peak intensity $I_\nu$ falls with distance $d$ from the core, following the relation, $I_\nu\propto d^a$, where $a$ is typically -1.5. Assuming that adiabatic expansion losses are primarily responsible for the jet intensity "dimming", two limiting cases are considered: [1] the jet has a constant speed on parsec-scales and is expanding gradually such that the jet radius $r\propto d^0.4$; this expansion is however unobservable in the laterally unresolved jets at 5 GHz, and [2] the jet is cylindrical and is accelerating on parsec-scales. Accelerating parsec-scale jets are consistent with the phenomenon of "magnetic driving" in Poynting flux dominated jets. Chandra observations of 15 UGC FRIs detect X-ray jets in nine of them. The high frequency of occurrence of X-ray jets in this complete sample suggests that they are a signature of a ubiquitous process in FRI jets.
The luminous blue variable (LBV) stars are peculiar very massive stars. The study of these stellar objects and their surroundings is important for understanding the evolution of massive stars and its effects on the interstellar medium. We study the LBV star candidate G26.47+0.02. Using several large-scale surveys in different frequencies we performed a multiwavelength study of G26.47+0.02 and its surroundings. We found a molecular shell (seen in the 13CO J=1-0 line) that partially surrounds the mid-infrared nebula of G26.47+0.02, which suggests an interaction between the strong stellar winds and the molecular gas. From the HI absorption and the molecular gas study we conclude that G26.47+0.02 is located at a distance of ~4.8 kpc. The radio continuum analysis shows a both thermal and non-thermal emission toward this LBV candidate, pointing to wind-wind collision shocks from a binary system. This hypothesis is supported by a search of near-IR sources and the Chandra X-ray analysis. Additional multiwavelength and long-term observations are needed to detect some possible variable behavior, and if that is found, to confirm the binary nature of the system.
We present the results of a study of selection criteria to identify Type Ia supernovae photometrically in a simulated mixed sample of Type Ia supernovae and core collapse supernovae. The simulated sample is a mockup of the expected results of the Dark Energy Survey. Fits to the MLCS2k2 and SALT2 Type Ia supernova models are compared and used to help separate the Type Ia supernovae from the core collapse sample. The Dark Energy Task Force Figure of Merit (modified to include core collapse supernovae systematics) is used to discriminate among the various selection criteria. This study of varying selection cuts for Type Ia supernova candidates is the first to evaluate core collapse contamination using the Figure of Merit. Different factors that contribute to the Figure of Merit are detailed. With our analysis methods, both SALT2 and MLCS2k2 Figures of Merit improve with tighter selection cuts and higher purities, peaking at 98% purity.
We utilize the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS) HST/ACS dataset for a Deep Rapid Archival Flare Transient Search (DRAFTS) to constrain the flare rate toward the older stellar population in the Galactic bulge. During 7 days of monitoring 229,293 stars brighter than V=29.5, we find evidence for flaring activity in 105 stars between V=20 and V=28. We divided the sample into non-variable stars and variable stars whose light curves contain large-scale variability. The flare rate on variable stars is \sim 700 times that of non-variable stars, with a significant correlation between the amount of underlying stellar variability and peak flare amplitude. The flare energy loss rates are generally higher than those of nearby well-studied single dMe flare stars. The distribution of proper motions is consistent with the flaring stars being at the distance and age of the Galactic bulge. If they are single dwarfs, they span a range of \approx 1.0 - 0.25M\odot. A majority of the flaring stars exhibit periodic photometric modulations with P <3d. If these are tidally locked magnetically active binary systems, their fraction in the bulge is enhanced by a factor of \sim20 compared to the local value. These stars may be useful for placing constraints on the angular momentum evolution of cool close binary stars. Our results expand the type of stars studied for flares in the optical band, and suggest that future sensitive optical time-domain studies will have to contend with a larger sample of flaring stars than the M dwarf flare stars usually considered.
We calculate the absolute intensity and anisotropies of the Lyman-$\alpha$ radiation field present during the epoch of reionization. We consider emission from both galaxies and the intergalactic medium (IGM) and take into account all of the contributions to the production of Lyman-$\alpha$ photons: recombinations, collisions, continuum emission from the stars and scattering of Lyman-n photons in the IGM. We find that the emission from individual galaxies dominates over the IGM with a total Lyman-$\alpha$ intensity of about $1.3\times 10^{-2}$ and $3.7\times10^{-3}$ nW m$^{-2}$ sr$^{-1}$ at a redshift of 7 and 10, respectively. These intensity levels are well below the extragalactic background intensity from starlight emission from galaxies and it is unlikely that the Lyman-$\alpha$ background during reionization can be established by an experiment aiming at an absolute background light measurement. Instead we consider Lyman-$\alpha$ intensity mapping with the aim of measuring the anisotropy power spectrum. The anisotropy power spectrum has rms fluctuations at the level of $10^{-2}$ nW m$^{-2}$ sr$^{-1}$ at a few Mpc scales. These anisotropies could be measured with a spectrometer at near-IR wavelengths from 0.9 to 1.4 $\mu$m with fields in the order of 0.5 to 1 sq. degrees. We recommend that existing ground-based programs using narrow band filters also pursue intensity fluctuations to study statistics on the spatial distribution of fainter Lyman-$\alpha$ emitters that remain below the individual detection threshold. We also discuss the cross-correlation signal with 21 cm experiments that probe HI in the IGM during reionization. A dedicated sub-orbital or space-based Lyman-$\alpha$ intensity mapping experiment could provide a viable complementary approach to probe reionization, when compared to 21 cm experiments.
Surface Brightness Fluctuations (SBFs) are one of the most powerful techniques to measure the distance and to constrain the unresolved stellar content of extragalactic systems. For a given bandpass, the absolute SBF magnitude \bar{M} depends on the properties of the underlying stellar population. Multi-band SBFs allow scientists to probe different stages of the stellar evolution: UV and blue wavelength band SBFs are sensitive to the evolution of stars within the hot Horizontal Branch (HB) and post-Asymptotic Giant Branch (post-AGB) phase, whereas optical SBF magnitudes explore the stars within the Red Giant Branch (RGB) and HB regime. Near- and Far-infrared SBF luminosities probe the important stellar evolution stage within the AGB and Thermally-Pulsating Asymptotic Giant Branch (TP-AGB) phase. Since the first successful application by Tonry and Schneider, a multiplicity of works have used this method to expand the distance scale up to 150 Mpc and beyond. This article gives a historical background of distance measurements, reviews the basic concepts of the SBF technique, presents a broad sample of these investigations and discusses possible selection effects, biases, and limitations of the method. In particular, exciting new developments and improvements in the field of stellar population synthesis are discussed that are essential to understand the physics and properties of the populations in unresolved stellar systems. Further, promising future directions of the SBF technique are presented. With new upcoming space-based satellites such as Gaia, the SBF method will remain as one of the most important tools to derive distances to galaxies with unprecedented accuracy and to give detailed insights into the stellar content of globular clusters and galaxies.
In this work we consider a gravitating scalar field, $\phi$ with a non-conventional kinetic term as in the string theory tachyon, an arbitrary potential, $V(\phi)$, and two measures -- a geometric measure ($\sqrt{-g}$) and a non-metric measure ($\Phi$). This model gives a unified picture of dark energy and dark matter. The model has two interesting features: (i) For potentials which are unstable and would give rise to tachyonic scalar field, this model can stabilize the scalar field. (ii) The form of the dark energy and dark matter that results from this model is fairly insensitive to the exact form of the scalar field potential.
We perform fully non-linear numerical simulations of charged-black-hole collisions, described by the Einstein-Maxwell equations, and contrast the results against analytic expectations. We focus on head-on collisions of non-spinning black holes, starting from rest and with the same charge to mass ratio, Q/M. The addition of charge to black holes introduces a new interesting channel of radiation and dynamics, most of which seem to be captured by Newtonian dynamics and flat-space intuition. The waveforms can be qualitatively described in terms of three stages; (i) an infall phase prior to the formation of a common apparent horizon; (ii) a nonlinear merger phase which corresponds to a peak in gravitational and electromagnetic energy; (iii) the ringdown marked by an oscillatory pattern with exponentially decaying amplitude and characteristic frequencies that are in good agreement with perturbative predictions. We observe that the amount of gravitational-wave energy generated throughout the collision decreases by about three orders of magnitude as the charge-to-mass ratio Q/M is increased from 0 to 0.98. We interpret this decrease as a consequence of the smaller accelerations present for larger values of the charge. In contrast, the ratio of energy carried by electromagnetic to gravitational radiation increases, reaching about 22% for the maximum Q/M ratio explored, which is in good agreement with analytic predictions.
Conventional SO(10) models involve more than one scale for a complete breaking of the GUT symmetry requiring further assumptions on the VEVs of the Higgs fields that enter in the breaking to achieve viable models. Recent works where the breaking can be accomplished at one scale are discussed. There include models with just a pair of $144+\bar{144}$ of Higgs fields. Further extensions of this idea utilizing $560+ \bar{560}$ of Higgs representations allow both the breaking at one scale, as well as accomplish a natural doublet-triplet splitting via the missing partner mechanism. More generally, we discuss the connection of high scale models to low energy physics in the context of supergravity grand unification. Here we discuss a natural solution to the little hierarchy problem and also discuss the implications of the LHC data for supersymmetry. It is shown that the LHC data implies that most of the parameter space of supergravity models consistent with the data lie on the Hyperbolic Branch of radiative breaking of the electroweak symmetry and more specifically on the Focal Surface of the Hyperbolic Branch. A discussion is also given of the implications of recent LHC data on the Higgs boson mass for the discovery of supersymmetry and for the search for dark matter.
We consider the Eddington-Born-Infeld (EBI) model here without assuming any cosmological constant. The EBI scalar field is supposed to play a role of both dark matter and dark energy. Different eras in cosmology are reconstructed for the model. A comparison is drawn with $\Lambda$CDM model using Supernova Ia, WMAP7 and BAO data. It seems that the EBI field in this form does not give good fit to observational data in comparison to the $\Lambda$CDM model.
A global view is given upon the study of collapsing shear-free perfect fluid spheres with heat flow. We apply a compact formalism, which simplifies the isotropy condition and the condition for conformal flatness. This formalism also presents the simplest possible version of the main junction condition, demonstrated explicitly for conformally flat and geodesic solutions. It gives the right functions to disentangle this condition into well known differential equations like those of Abel, Riccati, Bernoulli and the linear one. It yields an alternative derivation of the general solution with functionally dependent metric components. We bring together the results for static and time- dependent models to describe six generating functions of the general solution to the isotropy equation. Their common features and relations between them are elucidated. A general formula for separable solutions is given, incorporating collapse to a black hole or to a naked singularity.
[abridged] The detection of gravitational waves from extreme-mass-ratio (EMRI) binaries, comprising a stellar-mass compact object orbiting around a massive black hole, is one of the main targets for low-frequency gravitational-wave detectors in space, like the Laser Interferometer Space Antenna (LISA or eLISA/NGO). The long-duration gravitational-waveforms emitted by such systems encode the structure of the strong field region of the massive black hole, in which the inspiral occurs. The detection and analysis of EMRIs will therefore allow us to study the geometry of massive black holes and determine whether their nature is as predicted by General Relativity and even to test whether General Relativity is the correct theory to describe the dynamics of these systems. To achieve this, EMRI modeling in alternative theories of gravity is required to describe the generation of gravitational waves. In this paper, we explore to what extent EMRI observations with LISA or eLISA/NGO might be able to distinguish between General Relativity and a particular modification of it, known as Dynamical Chern-Simons Modified Gravity. Our analysis is based on a parameter estimation study that uses approximate gravitational waveforms obtained via a radiative-adiabatic method and is restricted to a five-dimensional subspace of the EMRI configuration space. This includes a Chern-Simons parameter that controls the strength of gravitational deviations from General Relativity. We find that, if Dynamical Chern-Simons Modified Gravity is the correct theory, an observatory like LISA or even eLISA/NGO should be able to measure the Chern-Simons parameter with fractional errors below 5%. If General Relativity is the true theory, these observatories should put bounds on this parameter at the level xi^(1/4) < 10^4 km, which is four orders of magnitude better than current Solar System bounds.
We discuss a supersymmetric version of DBI (Dirac-Born-Infeld) inflation, which is a typical inflation model in string cosmology. The supersymmetric DBI action together with a superpotential always leads to correction terms associated with the potential into the kinetic term, which drastically change the dynamics of DBI inflation. We find two significant features of supersymmetric DBI inflation. The first one is that ultra-relativistic motion is prohibited to cause inflation, which leads to order of unity sound velocity squared and hence small non-Gaussianities of primordial curvature perturbations. The second one is that the relation between the tensor-to-scalar ratio and the field variation is modified. Then, significant tensor-to-scalar ratio $r \gtrsim 0.01$ is possible even for sub-Planck variation of the field. These new features are in sharp contrast with those of the standard non-supersymmetric DBI inflation and hence have a lot of interest implications on upcoming observations of cosmic microwave background (CMB) anisotropies by the Planck satellite as well as direct detection experiments of gravitational waves like DECIGO and BBO.
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We examine the consequences of a model in which relativistic jets can be
triggered in quiescent massive black holes when a geometrically thick and hot
accretion disk forms as a result of the tidal disruption of a star. To estimate
the power, thrust and lifetime of the jet, we use the mass accretion history
onto the black hole as calculated by detailed hydrodynamic simulations of the
tidal disruption of stars. We go on to determine the states of the interstellar
medium in various types of quiescent galactic nuclei, and describe how this
external matter can affect jets propagating through it. We use this
information, together with a two-dimensional hydrodynamic model of the
structure of the relativistic flow, to study the dynamics of the jet, the
propagation of which is regulated by the density stratification of the
environment and by its injection history. The breaking of symmetry involved in
transitioning from one to two dimensions is crucial and leads to qualitatively
new phenomena. Many of the observed properties of the Swift 1644+57/GRB 110328A
event can be understood as resulting from accretion onto and jets driven by a
$10^6 M_\odot$ central mass black hole following the disruption of sun-like
star. With the inclusion of a stochastic contribution to the luminosity due to
variations in the feeding rate driven by instabilities near the tidal radius,
we find that our model can explain the X-ray light curve without invoking a
rarely-occurring deep encounter. In conjunction with the number density of
black holes in the local universe, we hypothesize that the conditions required
to produce the Swift event are not anomalous, but are in fact representative of
the jet-driven flare population arising from tidal disruptions.
[abridged]
Binary populations in young star clusters show multiplicity fractions both lower and up to twice as high as those observed in the Galactic field. We follow the evolution of a population of binary stars in dense and loose star clusters starting with an invariant initial binary population and a formal multiplicity fraction of unity, and demonstrate that these models can explain the observed binary properties in Taurus, Rho-Ophiuchus, Chamaeleon, Orion, IC 348, Upper Scorpius A, Praesepe, and the Pleiades. The model needs to consider solely different birth densities for these regions. The evolved theoretical orbital-parameter distributions are highly probable parent distributions for the observed ones. We constrain the birth conditions (stellar mass, M_ecl, and half-mass radius, r_h) for the derived progenitors of the star clusters and the overall present-day binary fractions allowed by the present model. The results compare very well with properties of molecular cloud clumps on the verge of star formation. Combining these with previously and independently obtained constraints on the birth densities of globular clusters, we identify a weak stellar mass -- half-mass radius correlation for cluster-forming cloud clumps, r_h / pc ~ (M_ecl / M_sun)^(0.13+-0.04). The ability of the model to reproduce the binary properties in all the investigated young objects, covering present-day densities from 1-10 stars pc^-3 (Taurus) to 2x10^4 stars pc^-3 (Orion), suggests that environment-dependent dynamical evolution plays an important role in shaping the present-day properties of binary populations in star clusters, and that the initial binary properties may not vary dramatically between different environments.
We report the discovery of two young M-dwarfs, RX J0942.7-7726 (M1) and 2MASS J09424157-7727130 (M4.5), that were found only 42 arcsec apart in a survey for pre-main sequence stars surrounding the open cluster eta Chamaeleontis. Both stars have congruent proper motions and near-infrared photometry. Medium-resolution spectroscopy reveals that they are coeval (age 8-12 Myr), codistant (100-150 pc) and thus almost certainly form a true wide binary with a projected separation of 4000-6000 AU. The system appears too old and dynamically fragile to have originated in eta Cha and a traceback analysis argues for its birth in or near the Scorpius-Centaurus OB Association. RX J0942.7-7726AB joins a growing group of wide binaries kinematically linked to Sco-Cen, suggesting that such fragile systems can survive the turbulent environment of their natal molecular clouds while still being dispersed with large velocities. Conversely, the small radial velocity difference between the stars (2.7 \pm 1.0 km/s) could mean the system is unbound, a result of the coincidental ejection of two single stars with similar velocity vectors from the OB association early in its evolution.
We present the results from a survey for 12CO emission in 40 luminous sub-millimetre galaxies (SMGs), with 850um fluxes of S850 = 4 - 20 mJy, conducted with the Plateau de Bure Interferometer. We detect 12CO emission in 32 SMGs at z~1.2 - 4.1, including 16 SMGs not previously published. Using multiple 12CO line (J_up =2 - 7) observations, we derive a median spectral line energy distribution for luminous SMGs and use this to estimate a mean gas mass of (5.3 +/- 1.0) \times 10^10 Msun. We report the discovery of a fundamental relationship between 12CO FWHM and 12CO line luminosity in high-redshift starbursts, which we interpret as a natural consequence of the baryon-dominated dynamics within the regions probed by our observations. We use far-infrared luminosities to assess the star-formation efficiency in our SMGs, finding a steepening of the L'CO-LFIR relation as a function of increasing 12CO J_up transition. We derive dynamical masses and molecular gas masses, and use these to determine the redshift evolution of the gas content of SMGs, finding that they do not appear to be significantly more gas rich than less vigorously star-forming galaxies at high redshifts. Finally, we collate X-ray observations, and study the interdependence of gas and dynamical properties of SMGs with their AGN activity and supermassive black hole masses (MBH), finding that SMGs lie significantly below the local M_BH-sigma relation. We conclude that SMGs represent a class of massive, gas-rich ultraluminous galaxies with somewhat heterogeneous properties, ranging from starbursting disc-like systems with L~10^12 L_sun, to the most highly star-forming mergers in the Universe.
Observed angular positions and redshifts of large-scale structure tracers such as galaxies are affected by gravitational waves through volume distortion and magnification effects. Thus, a gravitational wave background can in principle be probed through clustering statistics of large-scale structure. We calculate the observed angular clustering of galaxies in the presence of a gravitational wave background at linear order including all relativistic effects. For a scale-invariant spectrum of gravitational waves, the effects are most significant at the smallest multipoles (2 <= l <= 5), but typically suppressed by six or more orders of magnitude with respect to scalar contributions for currently allowed amplitudes of the inflationary gravitational wave background. We also discuss the most relevant second-order terms, corresponding to the distortion of tracer correlation functions by gravitational waves. These provide a natural application of the approach recently developed in arXiv:1204.3625.
Recent studies of massive-star forming regions indicate that they can contain multiple generations of young stars. These observations suggest that star formation in these regions is sequential and/or triggered by a previous generation of (massive) stars. Here we present new observations of the star forming region RCW 36 in the Vela Molecular Ridge, hosting a young cluster of massive stars embedded in a molecular cloud complex. In the periphery of the cluster several young stellar objects (YSOs) are detected which produce bipolar jets (HH 1042 and HH 1043) demonstrating that these objects are still actively accreting. The VLT/X-shooter spectrum of the jet structure of HH 1042 provides detailed information on the physical conditions and kinematical properties of the jet plasma. From this information the YSO's accretion history can be derived. Combining the photometric and spectroscopic observations of RCW 36 gives insight into the formation process of individual stars and the star formation history of this young massive-star forming region.
The B-(curl-)mode of the correlation of galaxy ellipticities (shear) can be used to detect a stochastic gravitational wave background, such as that predicted by inflation. In this paper, we derive the tensor mode contributions to shear from both gravitational lensing and intrinsic alignments, using the gauge-invariant, full-sky results of arXiv:1204.3625. We find that the intrinsic alignment contribution, calculated using the linear alignment model, is larger than the lensing contribution by an order of magnitude or more, if the alignment strength for tensor modes is of the same order as for scalar modes. This contribution also extends to higher multipoles. These results make the prospects for probing tensor modes using galaxy surveys less pessimistic than previously thought, though still very challenging.
[Abridged] We perform on galaxy mock catalogues the same colour-density (C-D) analysis made by Cucciati et al. (2006) on a 5 Mpc/h scale using the VVDS-Deep survey, and compare the results from mocks with observed data. We use mock catalogues with the same flux limits (I=24) as the VVDS (CMOCKS), built using the semi-analytic model by De Lucia & Blaizot (2007) applied to the Millennium Simulation. From CMOCKS, we extracted samples of galaxies mimicking the VVDS observational strategy (OMOCKS). We computed the B-band Luminosity Function LF and the C-D relation in the mocks. We find that the LF in mocks roughly agrees with the observed LF, but at z<0.8 the faint-end slope of the model LF is steeper than the VVDS one. Computing the LF for early and late type galaxies, we show that mocks have an excess of faint early-type and of bright late-type galaxies with respect to data. We find that the C-D relation in OMOCKS is in excellent agreement with the one in CMOCKS. At z~0.7, the C-D relation in mocks agrees with the VVDS one (red galaxies reside mainly in high densities). Yet, the strength of the C-D relation in mocks does not vary within 0.2<z<1.5, while the observed relation flattens with increasing z and possibly inverts at z=1.3. This suggests that in the model the C-D relation evolved at z>1.5, and/or that galaxy colour is affected by environment on scales <5 Mpc/h, and this is not mirrored on larger scales. The reversal of the C-D relation can be explained by wet mergers between young galaxies, producing a starburst event. This should be seen on group scales. A residual of this is found in observations at z=1.5 on larger scales (5 Mpc/h), but not in the mocks, suggesting that the treatment of environmental processes in models should be revised.
We present high spatial resolution maps of ro-vibrational molecular hydrogen emission from the environment of the GG Tau A binary component in the GG Tau quadruple system. The H2 v= 1-0 S(1) emission is spatially resolved and encompasses the inner binary, with emission detected at locations that should be dynamically cleared on several hundred-year timescales. Extensions of H2 gas emission are seen to ~100 AU distances from the central stars. The v = 2-1 S(1) emission at 2.24 microns is also detected at ~30 AU from the central stars, with a line ratio of 0.05 +/- 0.01 with respect to the v = 1-0 S(1) emission. Assuming gas in LTE, this ratio corresponds to an emission environment at ~1700 K. We estimate that this temperature is too high for quiescent gas heated by X-ray or UV emission from the central stars. Surprisingly, we find that the brightest region of H2 emission arises from a spatial location that is exactly coincident with a recently revealed dust "streamer" which seems to be transferring material from the outer circumbinary ring around GG Tau A into the inner region. As a result, we identify a new excitation mechanism for ro-vibrational H2 stimulation in the environment of young stars. The H2 in the GG Tau A system appears to be stimulated by mass accretion infall as material in the circumbinary ring accretes onto the system to replenish the inner circumstellar disks. We postulate that H2 stimulated by accretion infall could be present in other systems, particularly binaries and "transition disk" systems which have dust cleared gaps in their circumstellar environments.
We obtain lower limits on the amplitude of convective velocities in the deep solar convection zone based only on the observed properties of the differential rotation and meridional circulation together with simple and robust dynamical balances obtained from the fundamental MHD equations. The linchpin of the approach is the concept of gyroscopic pumping whereby the meridional circulation across isosurfaces of specific angular momentum is linked to the angular momentum transport by the convective Reynolds stress. We find that the amplitude of the convective velocity must be at least 30 m s$^{-1}$ in the upper CZ ($r \sim 0.95 R$) and at least 8 m s$^{-1}$ in the lower CZ ($r \sim 0.75 R$) in order to be consistent with the observed mean flows. Using the base of the near-surface shear layer as a probe of the rotational influence, we are further able to show that the characteristic length scale of deep convective motions must be no smaller than 5.5--30 Mm. These results are compatible with convection models but suggest that the efficiency of the turbulent transport assumed in advection-dominated flux-transport dynamo models is generally not consistent with the mean flows they employ.
We construct a series of model galaxies in rotational equilibrium consisting of gas, stars, and a fixed dark matter (DM) halo and study how these equilibrium systems depend on the mass and form of the DM halo, gas temperature, non-thermal and rotation support against gravity, and also on the redshift of galaxy formation. For every model galaxy we find the minimum gas mass M_g^min required to achieve a state in which star formation (SF) is allowed according to contemporary SF criteria. The obtained M_g^min--M_DM relations are compared against the baryon-to-DM mass relation M_b--M_DM inferred from the \LambdaCDM theory and WMAP4 data. Our aim is to construct realistic initial models of dwarf galaxies (DGs), which take into account the gas self-gravity and can be used as a basis to study the dynamical and chemical evolution of DGs. Rotating equilibria are found by solving numerically the steady-state momentum equation for the gas component in the combined gravitational potential of gas, stars, and DM halo using a forward substitution procedure. We find that for a given M_DM the value of M_g^min depends crucially on the gas temperature T_g, gas spin parameter \alpha, degree of non-thermal support \sigma_eff, and somewhat on the redshift for galaxy formation z_gf. Depending on the actual values of T_g, \alpha, \sigma_eff, and z_gf, model galaxies may have M_g^min that are either greater or smaller than M_b. Galaxies with M_DM \ga 10^9 M_sun are usually characterized by M_g^min \la M_b, implying that SF in such objects is a natural outcome as the required gas mass is consistent with what is available according to the \LambdaCDM theory. On the other hand, models with M_DM \la 10^9 M_sun are often characterized by M_g^min >> M_b, implying that they need much more gas than available to achieve a state in which SF is allowed. Abridged.
I endeavour to provide a thorough overview of our current knowledge of high-redshift galaxies and their evolution during the first billion years of cosmic time, corresponding to redshifts z > 5. After first summarizing progress with the seven different techniques which have been used to date in the discovery of objects at z > 5, I focus thereafter on the two selection methods which have yielded substantial samples of galaxies at early times, namely Lyman-break and Lyman-alpha selection. I discuss a decade of progress in galaxy sample selection at z ~ 5 - 8, including issues of completeness and contamination, and address some of the confusion which has been created by erroneous reports of extreme-redshift objects. Next I provide an overview of our current knowledge of the evolving ultraviolet continuum and Lyman-alpha galaxy luminosity functions at z ~ 5 - 8, and discuss what can be learned from exploring the relationship between the Lyman-break and Lyman-alpha selected populations. I then summarize what is known about the physical properties of these galaxies in the young universe, before considering the wider implications of this work for the cosmic history of star formation, and for the reionization of the universe. I conclude with a brief summary of the exciting prospects for further progress in this field in the next 5-10 years. Throughout, key concepts such as selection techniques and luminosity functions are explained assuming essentially no prior knowledge. The intention is that this chapter can be used as an introduction to the observational study of high-redshift galaxies, as well as providing a review of the latest results in this fast-moving research field up to the end of 2011.
We extend the 3-point intrinsic alignment self-calibration technique to the gravitational shear-intrinsic ellipticity-intrinsic ellipticity (GII) bispectrum. The proposed technique will allow the measurement and removal of the GII intrinsic alignment contamination from the cross-correlation weak lensing signal. While significantly decreased from using cross-correlations instead of auto-correlation in a single photo-z bin, the GII contamination persists in adjacent photo-z bins and must be accounted for and removed from the lensing signal. We relate the GII and galaxy density-intrinsic ellipticity-intrinsic ellipticity (gII) bispectra through use of the galaxy bias, and develop the estimator necessary to isolate the gII bispectrum from observations. We find that the GII self-calibration technique performs at a level comparable to that of the gravitational shear-gravitational shear-intrinsic ellipticity correlation (GGI) self-calibration technique, with measurement error introduced through the gII estimator generally negligible when compared to minimum survey error. The accuracy of the relationship between the GII and gII bispectra typically allows the GII self-calibration to reduce the GII contamination by a factor of 10 or more for all adjacent photo-z bin combinations at $\ell>300$. For larger scales, we find that the GII contamination can be reduced by a factor of 3-5 or more. The GII self-calibration technique is complementary to the existing GGI self-calibration technique, which together will allow the total intrinsic alignment cross-correlation signal in 3-point weak lensing to be measured and removed.
While major mergers and their tidal debris are well studied, they are less common than minor mergers (mass ratios < 0.3). The peculiar spiral NGC 2782 is the result of a merger between two disk galaxies with a mass ratio of ~4:1 occurring ~200 Myr ago. This merger produced a molecular and H I-rich, optically bright eastern tail and an H I-rich, optically faint western tail. Non-detection of CO in the western tail by Braine et al. suggested that star formation had not yet begun to occur in that tidal tail. However, deep H{\alpha} narrowband images show evidence of recent star formation in the western tail. Across the entire western tail, we find the global star formation rate per unit area ({\Sigma}SFR) to be several orders of magnitude less than expected from the total gas density. Together with extended FUV+NUV emission from Galaxy Evolution Explorer along the tail, this indicates a low global star formation efficiency in the tidal tail producing lower mass star clusters. The H II region that we observed has a local (few-kiloparsec scale) {\Sigma}SFR from H{\alpha} that is less than that expected from the total gas density, which is consistent with other observations of tidal debris. The star formation efficiency of this H II region inferred from the total gas density is low, but normal when inferred from the molecular gas density. These results suggest the presence of a very small, locally dense region in the western tail of NGC 2782 or of a low-metallicity and/or low-pressure star-forming region.
Several years of neutral particle measurements by the NASA/IBEX mission have yielded direct observations of interstellar neutral helium and oxygen. The data indicate the presence of secondary neutral helium and oxygen, which are created within the heliosphere by charge exchange involving helium or oxygen ions. This contribution describes a detailed conserving calculation method based on Keplerian orbits that has been developed to characterize helium distribution functions throughout the heliosphere, in particular in the innermost heliosphere, while accounting for loss and production of neutral particles along their path. Coupled with global heliosphere models of plasma distributions, this code is useful for predicting the fluxes of heavy neutral atoms at spacecraft detectors, so enabling inferences on the characteristics of the interstellar medium.
We present detailed spatially resolved measurements of the thermodynamic properties of the X-ray emitting gas in the inner regions of the five nearest, X-ray and optically brightest, and most X-ray morphologically relaxed giant elliptical galaxies known. Beyond the innermost region at r > 1 kpc, and out to r ~ 6 kpc, the density, pressure, entropy, and cooling time distributions for the X-ray emitting gas follow remarkably similar, simple, power-law like distributions. Notably, the entropy profiles follow a power-law form, with an index 0.92-1.07. The cumulative hot X-ray emitting gas mass profiles and the gas-mass to stellar-light ratios of all five galaxies are also similar. Overall the observed similarity of the thermodynamic profiles in this radial range argues that, in these systems, relativistic jets heat the gas at a similar rate averaged over time scales longer than the cooling time of 10^8 yr. These jets are powered by accretion from the hot gas, or material entrained within it, onto the central super-massive black hole. This jet heating creates an energy balance where heating and cooling are in equilibrium, keeping the hot galactic atmospheres in a `steady-state'. Within r < 1 kpc, this similarity breaks down: the observed entropy profiles show well resolved flattening and the values differ from system to system substantially. The accretion rate onto the black hole and the AGN activity, heating the interstellar medium, must therefore vary significantly on time scales shorter than the cooling time of 10^7 - 10^8 yr.
Detailed spectral analysis of the Galactic X-ray background emission, or the
Galactic Ridge X-ray Emission (GRXE), is presented. To study the origin of the
emission, broad-band and high-quality GRXE spectra were produced from 18
pointing observations with Suzaku in the Galactic bulge region, with the total
exposure of 1 Ms. The spectra were successfully fitted by a sum of two major
spectral components; a spectral model of magnetic accreting white dwarfs with a
mass of 0.66 (0.59-0.75) solar, and a softer optically-thin thermal emission
with a plasma temperature of 1.2-1.5 keV which is attributable to coronal X-ray
sources.
When combined with previous studies which employed high spatial resolution of
the Chandra satellite (e.g. Revnivtsev et al. 2009, Nature), the present
spectroscopic result gives another strong support to a scenario that the GRXE
is essentially an assembly of numerous discrete faint X-ray stars.
The detected GRXE flux in the hard X-ray band was used to estimate the number
density of the unresolved hard X-ray sources. When integrated over a luminosity
range of ~10^30-10^34 erg/s, the result is consistent with a value which was
reported previously by directly resolving faint point sources.
It has recently been suggested that chemical processing can shape the spatial distributions of complex molecules in the Orion-KL region and lead to the nitrogen-oxygen "chemical differentiation" seen in previous observations of this source. Orion-KL is a very dynamic region, and it is therefore also possible that physical conditions can shape the molecular distributions in this source. Only high spatial resolution observations can provide the information needed to disentangle these effects. Here we present millimeter imaging studies of Orion-KL at various beam sizes using the Combined Array for Research in Millimeter-Wave Astronomy (CARMA). We compare molecular images with high spatial resolution images that trace the temperature, continuum column density, and kinematics of the source in order to investigate the effects of physical conditions on molecular distributions. These observations were conducted at \lambda = 3 mm and included transitions of ethyl cyanide [C2H5CN], methyl formate [HCOOCH3], formic acid [HCOOH], acetone [(CH3)2CO], SiO, and methanol [CH3OH]. We find differences in the molecular distributions as a function of each of these factors. These results indicate that acetone may be produced by chemical processing and is robust to large changes in physical conditions, while formic acid is readily destroyed by gas-phase processing in warm and dense regions. We also find that while the spatial distributions of ethyl cyanide and methyl formate are not distinct as is suggested by the concept of "chemical differentiation", local physical conditions shape the small-scale emission structure for these species.
Here we present high spatial resolution (<1 arcsecond) observations of molecular emission in Orion-KL conducted using the Combined Array for Research in Millimeter-Wave Astronomy (CARMA). This work was motivated by recent millimeter continuum imaging studies of this region conducted at a similarly high spatial resolution, which revealed that the bulk of the emission arises from numerous compact sources, rather than the larger-scale extended structures typically associated with the Orion Hot Core and Compact Ridge. Given that the spatial extent of molecular emission greatly affects the determination of molecular abundances, it is important to determine the true spatial scale for complex molecules in this region. Additionally, it has recently been suggested that the relative spatial distributions of complex molecules in a source might give insight into the chemical mechanisms that drive complex chemistry in star-forming regions. In order to begin to address these issues, this study seeks to determine the spatial distributions of ethyl cyanide [C2H5CN], dimethyl ether [(CH3)2O], methyl formate [HCOOCH3], formic acid [HCOOH], acetone [(CH3)2CO], SiO, methanol [CH3OH], and methyl cyanide [CH3CN] in Orion-KL at \lambda = 3 mm. We find that for all observed molecules, the molecular emission arises from multiple components of the cloud that include a range of spatial scales and physical conditions. Here we present the results of these observations and discuss the implications for studies of complex molecules in star-forming regions.
We make use of four galaxy catalogs based on four different semi-analytical models (SAMs) implemented in the Millennium simulation to study the environmental effects and the model dependence of galaxy merger rate. We begin the analyses by finding that galaxy merger rate in the SAMs has mild redshift evolution, consistent with results of previous works. To study the environmental dependence of galaxy merger rate, we adopt two estimators, the local overdensity (1+{\delta}n) defined as the surface density from the nth-nearest-neighbor (n = 6 is chosen in this study) and the host halo mass Mh. We find that galaxy merger rate Fmg shows strong dependence on the local overdensity (1+{\delta}n) and the dependence is similar at all redshifts. For the overdensity estimator, the merger rate Fmg is found about twenty times larger in the densest regions than in under-dense ones in two of the four models while it is roughly four times higher in the other two. In other words, the discrepancies of the merger rate difference between two extremes can differ by a factor of ~ five depending on the SAMs adopted. On the other hand for the halo mass estimator, Fmg does not monotonically increase with the host halo mass Mh, but peaks in the $M_h$ range between 10^12 and 10^13 h-1 M{\Theta}, which corresponds to group environments. High merger rate in high local density regions corresponds primarily to the high merge rate in group environments......
Long-term variations of solar differential rotation and sunspot activity are investigated through re-analyzing the data on parameters of the differential rotation law obtained by Makarov, Tlatov, and Callebaut (1997), Javaraiah, Bertello, and Ulrich (2005a, b), and Javaraiah et al. (2009). Our results indicate that the solar surface rotation rate at the Equator (indicated by the A parameter of the standard solar rotation law) shows a secular decrease since cycle 12 onwards, given by about $1\,-\,1.5\times10^{-3}$($deg\ day^{-1} year^{-1}$). The B parameter of the standard differential rotation law seems to also show a secular decrease since cycle 12 onwards, but of weak statistical significance. The rotation rate averaged on latitudes ($0^{o}\,--\,40^{o}$) does not show a secular trend of statistical significance. Moreover, the average sunspot area shows a secular increase of statistical significance since cycle 12 onwards, while a negative correlation is found between the level of sunspot activity (indicated by the average sunspot area) and the solar equatorial rotation in the long run.
Relativistic jets propagating through an ambient medium must produce some observational effects along their side boundaries because of interactions across the large velocity gradient. One possible effect of such an interaction would be a sheared magnetic field structure at the jet boundaries, leading to a characteristic radio polarization pattern. As proposed by Ostrowski, another effect can come from the generation of a high energy cosmic ray component at the boundary, producing dynamic effects on the medium surrounding the jet and forming a cocoon dominated by cosmic rays with a decreased thermal gas emissivity. We selected this process for our first attempt to look for the effects of this type of interaction. We analyzed the Chandra X-ray data for the radio galaxy M87 in order to verify if the expected regions of diminished emissivity may be present near the spectacular X-ray jet in this source. The detailed analysis of the data, merged from 42 separate observations, shows signatures of lower emissivity surrounding the jet. In particular we detect an intensity dip along the part of the jet, which would be approximately 150 pc x 2 kpc in size, if situated along the jet which is inclined toward us. Due to a highly non-uniform X-ray background in the central region we are not able to claim the discovery of a cosmic ray cocoon around the M87 jet: we only have demonstrated that the data show morphological structures which could be accounted for if a cosmic ray cocoon exists.
A covariant formulation of a theory with a massive graviton and no negative energy state has been recently proposed as an alternative to the usual General Relativity framework. For a spatially flat homogenous and isotropic universe, the theory introduces modified Friedmann equations where the standard matter term is supplemented by four effective fluids mimicking dust, cosmological constant, quintessence and stiff matter, respectively. We test the viability of this massive gravity formulation by contrasting its theoretical prediction to the Hubble diagram as traced by Type Ia Supernovae (SNeIa) and Gamma Ray Bursts (GRBs), the $H(z)$ measurements from passively evolving galaxies, Baryon Acoustic Oscillations (BAOs) from galaxy surveys and the distance priors from the Cosmic Microwave Background Radiation (CMBR) anisotropy spectrum. It turns out that the model is indeed able to very well fit this large dataset thus offering a viable alternative to the usual dark energy framework. We finally set stringent constraints on its parameters also narrowing down the allowed range for the graviton mass.
The observational evidence for the acceleration of the universe demonstrates that canonical theories of gravitation and particle physics are incomplete, if not incorrect. The next generation of astronomical facilities must both be able to carry out precision consistency tests of the standard cosmological model and search for evidence of new physics beyond it. I describe some of these tests, and discuss prospects for facilities in which the CAUP Dark Side team is involved, specifically ESPRESSO, Euclid and CODEX.
Anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are magnetar candidates. During their studies, the magnetic dipole braking mechanism is often assumed. This will result in a high surface dipole field for most AXPs and SGRs. It will also bring several problems challenging the magnetar interpretation. Alternatively, it is possible that AXPs and SGRs are braked down by a particle wind which also originates from magnetic field decay. In the wind braking scenario, magnetars are neutron stars with strong multipole field. A strong dipole field is no longer required. Recent challenging observations of magnetars may be explained naturally in the wind braking scenario: (1) The supernova energetics of those associated with magnetars are of normal value; (2) The non-detection in Fermi observations of magnetars; (3) The problem posed by the low-magnetic field soft gamma-ray repeater; (4) The relation between magnetars and high magnetic field pulsars ; (5) A decreasing period derivative during magnetar outbursts etc. For magnetars with $L_{\rm x}<-\dot{E}_{\rm rot}$, they may still be magnetic dipole braking. This may explain the "fundamental plane" of magnetar radio emissions. A magnetism-powered (instead of rotation-powered) pulsar wind nebula will be one of the consequences of wind braking. For a magnetism-powered pulsar wind nebula, we should see a correlation between the nebula luminosity and the magnetar luminosity. This may be the case of the extended emission around AXP 1E 1547.0-5408. A braking index different from three is also calculated. Future braking index measurement of a magnetar may tell us whether magnetars are wind braking or magnetic dipole braking.
In a previous paper we identified cores within infrared dark clouds (IRDCs). We regarded those without embedded sources as the least evolved, and labelled them starless. Here we identify the most isolated starless cores and model them using a three-dimensional, multi-wavelength, Monte Carlo, radiative transfer code. We derive the cores' physical parameters and discuss the relation between the mass, temperature, density, size and the surrounding interstellar radiation field (ISRF) for the cores. The masses of the cores were found not to correlate with their radial size or central density. The temperature at the surface of a core was seen to depend almost entirely on the level of the ISRF surrounding the core. No correlation was found between the temperature at the centre of a core and its local ISRF. This was seen to depend, instead, on the density and mass of the core.
In this video we highlight the application of Computational Geometry to our
understanding of the formation and dynamics of the Cosmic Web. The emergence of
this intricate and pervasive weblike structure of the Universe on Megaparsec
scales can be approximated by a well-known equation from fluid mechanics, the
Burgers' equation. The solution to this equation can be obtained from a
geometrical formalism. We have extended and improved this method by invoking
weighted Delaunay and Voronoi tessellations. The duality between these
tessellations finds a remarkable and profound reflection in the description of
physical systems in Eulerian and Lagrangian terms.
The resulting Adhesion formalism provides deep insight into the dynamics and
topology of the Cosmic Web. It uncovers a direct connection between the
conditions in the very early Universe and the complex spatial patterns that
emerged out of these under the influence of gravity.
Infant mortality brought about by the expulsion of a star cluster's natal gas is widely invoked to explain cluster statistics at different ages. While a well studied problem, most recent studies of gas expulsion's effect on a cluster have focused on massive clusters, with stellar counts of order $10^4$. Here we argue that the evolutionary timescales associated with the compact low-mass clusters typical of the median cluster in the Solar neighborhood are short enough that significant dynamical evolution can take place over the ages usually associated with gas expulsion. To test this we perform {\it N}-body simulations of the dynamics of a very young star forming region, with initial conditions drawn from a large-scale hydrodynamic simulation of gravitational collapse and fragmentation. The subclusters we analyse have high local star formation efficiencies and are roughly virialised, and have populations of a few hundred stars. Over 10 Myr they expand to a similar degree as would be expected from gas expulsion if they were initially gas-rich, but the expansion is purely due to the internal stellar dynamics of the young clusters. The expansion is such that the stellar densities at 2 Myr match those of YSOs in the Solar neighborhood. We argue that at the low-mass end of the cluster mass spectrum, a deficit of clusters at 10s of Myr does not necessarily imply gas expulsion as a disruption mechanism.
SuperWASP light curves for 53 W UMa-type eclipsing binary (EB) candidates, identified in previous work as being close to the contact binary short-period limit, were studied for evidence of period change. The orbital periods of most of the stars were confirmed, and period decrease, significant at more than 5 sigma, was observed in three objects: 1SWASP J174310.98+432709.6 (-0.055 \pm0.003 s/yr), 1SWASP J133105.91+121538.0 (-0.075 \pm0.013 s/yr) and 1SWASP J234401.81-212229.1 (-0.313 \pm0.019 s/yr). The magnitudes of the observed period changes cannot be explained by magnetic braking or gravitational radiation effects, and are most likely primarily due to unstable mass transfer from primary to secondary components, possibly accompanied by unstable mass and angular momentum loss from the systems. If these period decreases persist, the systems could merge on a relatively short timescale.
Misaligned Active Galactic Nuclei (MAGNs), i.e., radio galaxies and quasars with the jet not directly pointing at the observer, are a new class of GeV emitters. In low power radio galaxies (i.e., FRIs), gamma-rays are mainly produced in compact jet regions, although in at least one case, Centaurus A, high energy photons from the radio lobes have been also observed. The first localization of the gamma-ray dissipation zone in a high power radio galaxy (i.e., FRII) excludes major contributions from extended regions. The study of the FRII source 3C111 indicates that gamma-ray photons are produced in the jet. The site, coincident with the radio core, is estimated to be at a distance <~0.3 pc from the black hole. Although the place where high energy photons are produced is probably similar in FRIs and FRIIs, high power radio galaxies are rarer in the GeV sky. Our study of all the radio sources belonging to four complete radio catalogs (3CR, 3CRR, MS4, 2Jy) disfavors the idea that the paucity of FRIIs is due to their larger distance (and therefore to their faintness) and supports other possibilities, pointing to beaming/jet structural differences between FRIs and FRIIs.
We present a simple heuristic model for the time-averaged soft X-ray temperature distribution in the accretion spot on the white dwarf in polars. The model is based on the analysis of the Chandra LETG spectrum of the prototype polar AM Her and involves an exponential distribution of the emitting area vs. blackbody temperature a(T) = a0 exp(-T/T0). With one free parameter besides the normalization, it is mathematically as simple as the single blackbody, but is physically more plausible and fits the soft X-ray and far-ultraviolet spectral fluxes much better. The model yields more reliable values of the wavelength-integrated flux of the soft X-ray component and the implied accretion rate than reported previously.
The Fermi-LAT satellite has recently discovered a small group of radio galaxies and steep spectrum radio sources: the misaligned AGNs (MAGNs) sample. We present the X-ray analysis of all the sources of this sample (7 FRIs and 3 FRIIs) with a firm GeV association. This study supports the idea that FRIIs host more efficient accretion mechanisms (m_dot >0.1) than FRIs (m_dot <0.003). Furthermore, in objects with high accretion rates the Broad Line Regions appear to be very active zones where, in addition to optical lines, the fluorescence iron Kalpha feature at 6.4 keV is also produced. It seems that the FRII jets propagate in an environment very rich in photons, explaining, at least at zeroth order, why the External Compton is the preferred mechanism to produce gamma-rays. In FRIs, where also the iron line is difficult to be detected, the paucity of photons in the circumnuclear ambient seems to favor the Synchrotron Self Compton process.
We present the results of a series of cosmological $N$-body simulations of a Vector Dark Energy (VDE) model, performed using a suitably modified version of the publicly available \texttt{GADGET}-2 code. The setups of our simulations were calibrated pursuing a twofold aim: 1) to analyze the large scale distribution of massive objects and 2) to determine the properties of halo structure in this different ramework.We observe that structure formation is enhanced in VDE, since the mass function at high redshift is boosted up to a factor of ten with respect to \LCDM, possibly alleviating tensions with the observations of massive clusters at high redshifts and early reionization epoch. Significant differences can also be found for the value of the growth factor, that in VDE shows a completely different behaviour, and in the distribution of voids, which in this cosmology are on average smaller and less abundant. We further studied the structure of dark matter haloes more massive than $5\times10^{13}$\hMsun, finding that no substantial difference emerges when comparing spin parameter, shape, triaxiality and profiles of structures evolved under different cosmological pictures. Nevertheless, minor differences can be found in the concentration-mass relation and the two point correlation function; both showing different amplitudes and steeper slopes.Using an additional series of simulations of a \LCDM\ scenario with the same $\Omega_M$ and $\sigma_8$ used in the VDE cosmology, we have been able to establish whether the modifications induced in the new cosmological picture were due to the particular nature of the dynamical dark energy or a straightforward consequence of the cosmological parameters.
A 50 min time series of one-dimensional slit-spectrograms, taken in quiet sun at disk center, observed at the German Vacuum Tower Telescope (Observatorio del Teide), was used to study the global and spatial variations of different line parameters. In order to determine the vertical structure of the photosphere two lines with well separated formation heights have been considered. The data have been filtered of p-modes to isolate the pure convective phenomenon. From our studies of global correlation coefficients and coherence and phase shift analyzes between the several line parameters, the following results can be reported. The convective velocity pattern preserves structures larger than 1.0" up to the highest layers of the photosphere (~ 435 km). However, at these layers, in the intensity pattern only structures larger than 2.0" are still connected with those at the continuum level although showing inverted brightness contrast. This confirms an inversion of temperature that we have found at a height of ~140 km. A possible evidence of gravity waves superimposed to the convective motions is derived from the phase shift analysis. We interpret the behavior of the full width at half maximum and the equivalent width as a function of the distance to the granular borders, as a consequence of enhanced turbulence and/or strong velocity gradients in the intergranular lanes.
From the inversion of a time series of high resolution slit spectrograms obtained from the quiet sun, the spatial and temporal distribution of the thermodynamical quantities and the vertical flow velocity is derived as a function of logarithmic optical depth and geometrical height. Spatial coherence and phase shift analyzes between temperature and vertical velocity depict the height variation of these physical quantities for structures of different size. An average granular cell model is presented, showing the granule-intergranular lane stratification of temperature, vertical velocity, gas pressure and density as a function of logarithmic optical depth and geometrical height. Studies of a specific small and a specific large granular cell complement these results. A strong decay of the temperature fluctuations with increasing height together with a less efficient penetration of smaller cells is revealed. The T -T coherence at all granular scales is broken already at log tau =-1 or z~170 km. At the layers beyond, an inversion of the temperature contrast is revealed. Vertical velocities are in phase throughout the photosphere and penetrate into the highest layers under study.
We present a comparison of the parameters of accretion disc outflows and the jet of the broad-line radio galaxy 3C 111 on sub-pc scales. We make use of published X-ray observations of ultra-fast outflows (UFOs) and new 43GHz VLBA images to track the jet knots ejection. We find that the superluminal jet coexists with the mildly relativistic outflows on sub-pc scales, possibly indicating a transverse stratification of a global flow. The two are roughly in pressure equilibrium, with the UFOs potentially providing additional support for the initial jet collimation. The UFOs are much more massive than the jet, but their kinetic power is probably about an order of magnitude lower, at least for the observations considered here. However, their momentum flux is equivalent and both of them are powerful enough to exert a concurrent feedback impact on the surrounding environment. A link between these components is naturally predicted in the context of MHD models for jet/outflow formation. However, given the high radiation throughput of AGNs, radiation pressure should also be taken into account. From the comparison with the long-term 2-10keV RXTE light curve we find that the UFOs are preferentially detected during periods of increasing flux. We also find the possibility to place the UFOs within the known X-ray dips-jet ejection cycles, which has been shown to be a strong proof of the disc-jet connection, in analogue with stellar-mass black holes. However, given the limited number of observations presently available, these relations are only tentative and additional spectral monitoring is needed to test them conclusively.
Signatures of the dissipation region of collisionless magnetic reconnection are investigated by the Geotail spacecraft for the 15 May 2003 event. The energy dissipation in the rest frame of the electron's bulk flow is considered in an approximate form D*_e, which is validated by a particle-in-cell simulation. The dissipation measure is directly evaluated from the {plasma moments}, the electric field, and the magnetic field. Using D*_e, a compact dissipation region is successfully detected in the vicinity of the possible X-point in Geotail data. The dissipation rate is 45 pWm**{-3}. The length of the dissipation region is estimated to 1--2 local ion inertial length. The Lorentz work W, the work rate by Lorentz force to plasmas, is also introduced. It is positive over the reconnection region and it has a peak around the pileup region away from the X-point. These new measures D*_e and W provide useful information to understand the reconnection structure.
More than 40 years after the discovery of Isolated Neutron Stars, the comprehension of their physics is still rather poor. This thesis is based on a program of multiwavelength observations of pulsars which yielded new and important pieces of information about the overall proprieties of this class of sources. The thesis is organized as follows: - In chapter 1 we give a very brief overview of the current status of the understanding of Isolated Neutron Stars. We also talk about the Fermi revolution that occurred in the last three years, focusing on the Fermi contribution to the knowledge of neutron stars. Then, we describe the results led by the synergy between X-ray and gamma-ray bands. - In chapter 2 we report two of our published papers containing the surprising results we obtained for two different radio-quiet pulsars. Such neutron stars, J0007+7303 and J0357+3205, can be considered "extreme" in the Fermi pulsars' zoo due to their energetics and ages. Both the X-ray observations and analyses are very different so that they can be considered as the standing-up examples of all the following analyses. - In chapter 3 we describe the analysis we done in the X-ray band and briefly report the obtained spectra of each pulsar and its nebula, if present. Then, we study the X-ray and gamma-ray pulsars' luminosities as a function of their rotational energies and ages in order to find any relationship between these values and any difference between the two populations of radio-quiet and radio-loud pulsars. - In chapter 4 we report the "identity card" of all Fermi pulsars, the detailed description of the analyses done and results obtained for each pulsar. Finally, in appendix we report our accepted proposals of the most significative X-ray observations used in this thesis plus the article on the X-ray behaviour of Fermi/LAT pulsars we published on the Astrophyisical Journal.
We report on the detection of infrared light from the super-Earth 55 Cnc e, based on four occultations obtained with Warm Spitzer at 4.5 microns. Our data analysis consists of a two-part process. In a first step, we perform individual analyses of each dataset and compare several baseline models to optimally account for the systematics affecting each lightcurve. We apply independent photometric correction techniques, including polynomial detrending and pixel-mapping, that yield consistent results at the 1-sigma level. In a second step, we perform a global MCMC analysis including all four datasets, that yields an occultation depth of 131+-28ppm, translating to a brightness temperature of 2360+-300 K in the IRAC-4.5 micron channel. This occultation depth suggests a low Bond albedo coupled to an inefficient heat transport from the planetary dayside to the nightside, or else possibly that the 4.5-micron observations probe atmospheric layers that are hotter than the maximum equilibrium temperature (i.e., a thermal inversion layer or a deep hot layer). The measured occultation phase and duration are consistent with a circular orbit and improves the 3-sigma upper limit on 55 Cnc e's orbital eccentricity from 0.25 to 0.06.
Radio emission at around 90 GHz from star-forming galaxies is expected to be strongly dominated by the free-free component due to ionising radiation from massive, short-lived, stars. We present high surface-brightness sensitivity observations at 90 GHz of the nearby star-forming galaxy Messier 66 with resolution of about 9 arcsec (corresponding to a physical scale of about 500 pc) and analyse these observations in combination with archival lower frequency radio and mid-infrared measurements. For the four regions for which the observations support our models we find that the free-free component indeed dominates the emission at 90 GHz, making up 76--90 per cent of the luminosity at this frequency but with the data also consistent with all of the emission being due to free-free. The estimates of free-free luminosities are also consistent, within measurement and decomposition errors, with star-formation rates derived from lower radio frequencies and mid-infrared observations. In our analysis we consider both power-law and curved spectra for the synchrotron component but do not find evidence to support the curved model in preference to the power-law.
We compare the determinations of the angular momentum of stellar mass black holes via the continuum and line methods with those from diskoseismology. The assumption that is being tested is that one of the QPOs (quasi-periodic oscillations) in each binary X-ray source is produced by the fundamental g-mode. This should be the most robust and visible normal mode of oscillation of the accretion disk, and therefore its absence should rule out diskoseismology as the origin of QPOs. The comparisons are consistent with the second highest frequency QPO being produced by this g-mode, but are not consistent with models in which the QPO frequency is that of the innermost stable circular orbit.
We confirm the detection of 3 groups in the Lynx supercluster, at z~1.3, and give their redshifts and masses. We study the properties of the group galaxies as compared to the central clusters, RXJ0849+4452 and RXJ0848+4453, selecting 89 galaxies in the clusters and 74 galaxies in the groups. We morphologically classify galaxies by visual inspection, noting that our early-type galaxy (ETG) sample would have been contaminated at the 30% -40% level by simple automated classification methods (e.g. based on Sersic index). In luminosity selected samples, both clusters and groups show high fractions of Sa galaxies. The ETG fractions never rise above ~50% in the clusters, which is low compared to the fractions observed in clusters at z~1. However, ETG plus Sa fractions are similar to those observed for ETGs in clusters at z~1. Bulge-dominated galaxies visually classified as Sas might also be ETGs with tidal features or merger remnants. They are mainly red and passive, and span a large range in luminosity. Their star formation seems to have been quenched before experiencing a morphological transformation. Because their fraction is smaller at lower redshifts, they might be the spiral population that evolves into ETGs. For mass-selected samples, the ETG fraction show no significant evolution with respect to local clusters, suggesting that morphological transformations occur at lower masses and densities. The ETG mass-size relation shows evolution towards smaller sizes at higher redshift in both clusters and groups, while the late-type mass-size relation matches that observed locally. The group ETG red sequence shows lower zero points and larger scatters than in clusters, both expected to be an indication of a younger galaxy population. The estimated age difference is small when compared to the difference in age at different galaxy masses.
We define a distinguished "ground state" or "vacuum" for a free scalar quantum field in a globally hyperbolic region of an arbitrarily curved spacetime. Our prescription is motivated by the recent construction of a quantum field theory on a background causal set using only knowledge of the retarded Green's function. We generalize that construction to continuum spacetimes and find that it yields a distinguished vacuum or ground state for a non-interacting, massive or massless scalar field. This state is defined for all compact regions and for many noncompact ones. In a static spacetime we find that our vacuum coincides with the usual ground state. We determine it also for a radiation-filled, spatially homogeneous and isotropic cosmos, and show that the super-horizon correlations are approximately the same as those of a thermal state. Finally, we illustrate the inherent non-locality of our prescription with the example of a spacetime which sandwiches a region with curvature in-between flat initial and final regions.
Extensions of the Standard Model with an extra U'(1) abelian group generically generate terms coming from loops of heavy fermions, leading to three gauge boson couplings, in particular Z'Z gamma. We show that WMAP data constrains the gauge coupling of the group g_D to values comparable with the electro-weak ones, rather independently of the mass of Z'. Moreover, the model predicts a monochromatic gamma-ray line which can fit a 130 GeV signal at the FERMI telescope for natural values of the Chern-Simons terms and a dark matter mass around 144.5 GeV.
We study the multifield inflationary models where the cosmological perturbation is sourced by light scalar fields other than the inflaton. The corresponding perturbations are both scale invariant and special conformally invariant. We exploit the operator product expansion technique of conformal field theories to study the inflationary correlators enjoying the symmetries present during the de Sitter epoch. The operator product expansion is particularly powerful in characterizing inflationary correlation functions in two observationally interesting limits, the squeezed limit of the three-point correlator and the collapsed limit of the four-point correlator. Despite the fact that the shape of the four-point correlators is not fixed by the symmetries of de Sitter, its exact shape can be found in the collapsed limit making use of the operator product expansion. By employing the fact that conformal invariance imposes the two-point cross-correlations of the light fields to vanish unless the fields have the same conformal weights, we are able to show that the Suyama-Yamaguchi inequality relating the coefficients $f_{\rm NL}$ of the bispectrum in the squeezed limit and $\tau_{\rm NL}$ of the trispectrum in the collapsed limit also holds when the light fields are intrinsically non-Gaussian. In fact, we show that the inequality is valid irrespectively of the conformal symmetry, being just a consequence of fundamental physical principles, such as the short-distance expansion of operator products. The observation of a strong violation of the inequality will then have profound implications for inflationary models as it will imply either that multifield inflation cannot be responsible for generating the observed fluctuations independently of the details of the model or that some new non-trivial degrees of freedom play a role during inflation.
Extra-dimensional scenarios have become widespread among particle and gravitational theories of physics to address several outstanding problems, including the dark energy or weak hierarchy problems. In general, the topology and geometry of the full spacetime manifold will be non-trivial, even if our ordinary dimensions have the topology of their covering space. Most compact manifolds are inhomogeneous, even if they admit a homogeneous geometry, and it will be physically relevant where in the extra-dimensions one is located. In this letter, we explore the use of the Casimir effect in a braneworld scenario as a dynamical mechanism to determine and stabilize the location of a single brane. This is possible because the zero point energy in bulk quantum fields that satisfy particular brane boundary conditions depends on the brane location. Thus, there is a position-dependent force on the brane. Here we consider the 2-dimensional horn as a toy model of the extra dimensions and calculate the Casimir energy for a bulk scalar satisfying a Dirchlet boundary condition on a brane that wraps around the horn. For brane tensions above a critical value, a stable energy minimum is achieved as a result of the competition between the Casimir energy and the brane tension. We discuss this as an example of physics that is neither local nor global, but regional.
We present some exact solutions of the Einstein equations with anisotropic fluid exploiting the Chaplygin equation of state. The solutions describe spacetimes with two identical T regions and an intermediate static spherically symmetric R region containing a wormhole. The metric in the T region represents an anisotropic Kantowski-Sachs cosmological model. Its evolution starts from an event horizon and develops according to different scenarios including eternal expansion, contraction and also a finite universe lifetime.
Inflation in an open universe produced by Coleman-De Luccia (CDL) tunneling induces a friction term that is strong enough to allow for successful small-field inflation in models that would otherwise suffer from a severe overshoot problem. In this paper, we present a polynomial scalar potential which allows for a full analysis. This provides a simple model of single-field open inflation on a small-field inflection point after tunneling. We present numerical results and compare them with analytic approximations.
Nano and micro meter sized dust particles travelling through the heliosphere at several hundreds of km/s have been repeatedly detected by interplanetary spacecraft. When such fast moving dust particles hit a solid target in space, an expanding plasma cloud is formed through the vaporisation and ionisation of the dust particles itself and part of the target material at and near the impact point. Immediately after the impact the small and dense cloud is dominated by collisions and the expansion can be described by fluid equations. However, once the cloud has reached micro-m dimensions, the plasma may turn collisionless and a kinetic description is required to describe the subsequent expansion. In this paper we explore the late and possibly collisionless spherically symmetric unconstrained expansion of a single ionized ion-electron plasma using N-body simulations. Given the strong uncertainties concerning the early hydrodynamic expansion, we assume that at the time of the transition to the collisionless regime the cloud density and temperature are spatially uniform. We do also neglect the role of the ambient plasma. This is a reasonable assumption as long as the cloud density is substantially higher than the ambient plasma density. In the case of clouds generated by fast interplanetary dust grains hitting a solid target some 10^7 electrons and ions are liberated and the in vacuum approximation is acceptable up to meter order cloud dimensions. ...
Evidence continues to grow in MiniBooNE (MB) data favoring neutrino oscillations consistent with LSND. At least one sterile neutrino is required to explain the anomalies consistent with the observations of other experiments. At the same time, there is a strong tension between the positive signals of LSND and MB and the null results of nu_e and nu_mu disappearance experiments. We explore a scenario, first proposed in \cite{Nelson:2010hz}, where the presence of an additional heavy sterile neutrino (with mass well above an eV) can alleviate tension between LSND, MB and the null results of disappearance experiments. We compare and contrast this 3+1+1 scenario with the more standard 3+1 scenario and carry out global fits to all oscillation data including new 2011 MB anti-nu data. We find that the tension can be somewhat alleviated and that a phenomenologically viable window for the heavy neutrino, consistent with rare decays and BBN constraints, can be found if the fifth neutrino has a mass of order 0.3 - 10 GeV. We also find, however, that the 2011 MB anti-nu data exacerbates the tension with null experiments in both the 3+1 and 3+1+1 models when the lowest energy bins are included, resulting in little improvement in the global fit. We also discuss the implications of a heavy fifth neutrino for the reactor and gallium anomalies.
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Dark matter haloes in cosmological N-body simulations are affected by processes such as mergers, accretion and the gravitational interaction with baryonic matter. In typical analyses of dark matter haloes, the velocity distributions are assumed to be spherically symmetric. The validity of this assumption has, however, not been explicitly tested. We derive properties of particles in cones parallel or perpendicular to the collision axis of merger remnants. We find that the velocity anisotropy, which describes differences in the radial and tangential velocity dispersion, has a strong dependence on direction. The finding that the direction-dependence of the velocity anisotropy of a halo depends on the merger history, explain why a large diversity is seen in the velocity anisotropy profiles in the outer parts of high-resolution simulations of cosmological haloes.
We explore the origin of mid-infrared (mid-IR) dust extinction in all 20 nearby (z < 0.05) bona-fide Compton-thick (N_H > 1.5 x 10^24 cm^-2) AGN with hard energy (E > 10 keV) X-ray spectral measurements. We accurately measure the silicate absorption features at lambda~9.7um in archival low-resolution (R~57-127) Spitzer Infrared Spectrograph (IRS) spectroscopy, and show that only a minority (~45%) of nearby Compton-thick AGN have strong Si-absorption features (S_9.7 = ln(f_{int}/f_{obs}) > 0.5) which would indicate significant dust attenuation. The majority (~60%) are star-formation dominated (AGN:SB<0.5) at mid-IR wavelengths and lack the spectral signatures of AGN activity at optical wavelengths, most likely because the AGN emission-lines are optically-extinguished. Those Compton-thick AGN hosted in low-inclination angle galaxies exhibit a narrow-range in Si-absorption (S_9.7 ~ 0-0.3), which is consistent with that predicted by clumpy-torus models. However, on the basis of the IR spectra and additional lines of evidence, we conclude that the dominant contribution to the observed mid-IR dust extinction is dust located in the host galaxy (i.e., due to disturbed morphologies; dust-lanes; galaxy inclination angles) and not necessarily a compact obscuring torus surrounding the central engine.
We present integral field spectroscopy observations, covering the [O III]4959,5007 emission-line doublet of eight high-redshift (z=1.4-3.4) ultra-luminous infrared galaxies (ULIRGs) that host active galactic nuclei (AGN) activity, including known sub-millimetre luminous galaxies (SMGs). The targets have moderate radio luminosities that are typical of high-redshift ULIRGs (L[1.4GHz]=10^24-10^25 W/Hz) and therefore are not radio-loud AGN. We de-couple kinematic components due to the galaxy dynamics and mergers from those due to outflows. We find evidence in the most luminous systems, L([O III])\gtrsim10^43 erg/s, for the signatures of large-scale energetic outflows: extremely broad [O III] emission (FWHM \sim 700-1400 km/s) across \sim4-15 kpc, with high velocity offsets from the systemic redshifts (up to \sim850 km/s). These outflows are potentially depositing energy into their host galaxies at considerable rates (\sim10^43-10^45 erg/s) and are likely to unbind some of the gas from the host galaxies. Based on energetic arguments we find that the radiative power of the AGN, as opposed to star formation or radio jets, is likely to dominate in driving these outflows. We suggest that the galaxies observed may represent a key stage in the evolution of massive galaxies.
We use the distribution of extrasolar planets in circular orbits around stars with surface convective zones detected by ground based transit searches to constrain how efficiently tides raised by the planet are dissipated on the parent star. We parameterize this efficiency as a tidal quality factor (Q*). We conclude that the population of currently known planets is inconsistent with Q*<10^7 at the 99% level. Previous studies show that values of Q* between 10^5 and 10^7 are required in order to explain the orbital circularization of main sequence low mass binary stars in clusters, suggesting that different dissipation mechanisms might be acting in the two cases, most likely due to the very different tidal forcing frequencies relative to the stellar rotation frequency occurring for star--star versus planet--star systems.
We present analysis of 4U 1626-67, a 7.7 s pulsar in a low-mass X-ray binary system, observed with the hard X-ray detector of the Japanese X-ray satellite Suzaku in March 2006 for a net exposure of \sim88 ks. The source was detected at an average 10-60 keV flux of \sim4 x10^-10 erg cm^-2 s^-1. The phase-averaged spectrum is reproduced well by combining a negative and positive power-law times exponential cutoff (NPEX) model modified at \sim 37 keV by a cyclotron resonance scattering feature (CRSF). The phase-resolved analysis shows that the spectra at the bright phases are well fit by the NPEX with CRSF model. On the other hand, the spectrum in the dim phase lacks the NPEX high-energy cutoff component, and the CRSF can be reproduced by either an emission or an absorption profile. When fitting the dim phase spectrum with the NPEX plus Gaussian model, we find that the feature is better described in terms of an emission rather than an absorption profile. The statistical significance of this result, evaluated by means of an F-test, is between 2.91 x 10^-3 and 1.53 x 10^-5, taking into account the systematic errors in the background evaluation of HXD-PIN. We find that, the emission profile is more feasible than the absorption one for comparing the physical parameters in other phases. Therefore, we have possibly detected an emission line at the cyclotron resonance energy in the dim phase.
We explore possible systematic errors in the mass measurements of stellar mass black holes. We find that significant errors can arise from the assumption of zero or constant emission from the accretion flow, which is commonly used when determining orbital inclination by modelling ellipsoidal variations. For A0620-00, the system with the best available data, we show that typical data sets and analysis procedures can lead to systematic underestimates of the inclination by ten degrees or more. A careful examination of the available data for the 15 other X-ray transients with low-mass donors suggests that this effect may significantly reduce the black hole mass estimates in several other cases, most notably that of GRO J0422+32. With these revisions, our analysis of the black hole mass distribution in soft X-ray transients does not suggest any "mass gap" between the low end of the distribution and the maximum theoretical neutron star mass, as has been identified in previous studies. Nevertheless, we find that the mass distribution retains other previously identified characteristics, namely a peak around 8M\odot, a paucity of sources with masses below 5M\odot, and a sharp drop-off above 10M\odot.
We report Herschel SPIRE (250, 350, and 500 micron) detections of 32 quasars with redshifts 0.5 < z < 3.6 from the Herschel Multi-tiered Extragalactic Survey. These sources are from a MIPS 24 micron flux-limited sample of 326 quasars in the Lockman Hole Field. The extensive multi-wavelength data available in the field permit construction of the rest-frame Spectral Energy Distributions (SEDs)from ultraviolet to the mid-infrared for all sources, and to the far-infrared (FIR) for the 32 objects. Most quasars with Herschel FIR detections show dust temperatures in the range of 25K to 60K, with a mean of 34K. The FIR luminosities range from 10^{11.3} to 10^{13.5} Lsun, qualifying most of their hosts as ultra- or hyper-luminous infrared galaxies. These FIR-detected quasars may represent a dust-rich population, but with lower redshifts and fainter luminosities than quasars observed at ~ 1 mm. However, their FIR properties cannot be predicted from shorter wavelengths (0.3--20 micron, rest-frame), and the bolometric luminosities derived using the 5100 A index may be underestimated for these FIR-detected quasars. Regardless of redshift, we observed a decline in the relative strength of FIR luminosities for quasars with higher near-infrared luminosities.
Using the sample presented in Pan:2011, we analyse the photometric properties of 88,794 void galaxies and compare them to galaxies in higher density environments with the same absolute magnitude distribution. In Pan et al. (2011), we found a total of 1054 dynamically distinct voids in the SDSS with radius larger than 10h^-1 Mpc. The voids are underdense, with delta rho/rho < -0.9 in their centers. Here we study the photometric properties of these void galaxies. We look at the u - r colours as an indication of star formation activity and the inverse concentration index as an indication of galaxy type. We find that void galaxies are statistically bluer than galaxies found in higher density environments with the same magnitude distribution. We examine the colours of the galaxies as a function of magnitude, and we fit each colour distribution with a double-Gaussian model for the red and blue subpopulations. As we move from bright to dwarf galaxies, the population of red galaxies steadily decreases and the fraction of blue galaxies increases in both voids and walls, however the fraction of blue galaxies in the voids is always higher and bluer than in the walls. We also split the void and wall galaxies into samples depending on galaxy type. We find that late type void galaxies are bluer than late type wall galaxies and the same holds for early galaxies. We also find that early type, dwarf void galaxies are blue in colour. We also study the properties of void galaxies as a function of their distance from the center of the void. We find very little variation in the properties, such as magnitude, colour and type, of void galaxies as a function of their location in the void. The only exception is that the dwarf void galaxies may live closer to the center. The centers of voids have very similar density contrast and hence all void galaxies live in very similar density environments (ABRIDGED)
In this third paper in a series of three, we present a detailed study of the
AGN broadband SED based on a nearby unobscured Type 1 AGN sample. We perform a
systematic cross-correlation study of the following key parameters:
$\Gamma_{2-10keV}$, $L_{2-10keV}$, $L_{bol}$, $L_{bol}/L_{Edd}$,
$\kappa_{2-10keV}$, $\kappa_{5100A}$, FWHM$_{H\beta}$, M$_{BH}$, $\alpha_{ox}$,
$\alpha_{X}$ and $\alpha_{UV}$, and identify various strong correlations among
these parameters. The principal component analysis (PCA) is performed on the
correlation matrix of the above parameters, which shows that the three physical
parameters, i.e. black hole mass, mass accretion rate and Eddington ratio,
drive the majority of the correlations. This is consistent with PCA results
found from previous optical spectral studies.
We produce various mean SEDs classified by each of the key parameters. Most
parameters, except L$_{bol}$, show similar systematic changes in the mean SEDs
such that the temperature at which the disc peaks is correlated with the ratio
of power in the disc versus the Comptonised components and the hard X-ray
spectral index. This underlying change in SED shape shows that AGN do exhibit
intrinsically different spectral states. This is superficially similar to the
SED differences in BHB seen as $\lambda_{Edd}$ increases, but the analogy does
not hold in detail. Only objects with the highest $\lambda_{Edd}$ appear to
correspond to a BHB spectral state (the disc dominated high/soft state). The
AGN with typical mass accretion rates have spectra which do not match well with
any state observed in BHB. We speculate that this could be due to the presence
of a powerful UV line driven disc wind, which complicates simple mass scaling
between stellar and supermassive black holes.
Current sheets thinner than the ion inertial length are unstable to the tearing instability and will develop magnetic islands that grow due to magnetic reconnection. We investigate whether the growth of magnetic islands in a current sheet can continue indefinitely, or in the case of the heliosheath until reaching a neighboring current sheet, and at what rate the islands grow. We investigate the development and growth of magnetic islands using a particle-in-cell code, starting from particle noise. Performing a scaling of the growth of magnetic islands versus the system size, we find that the growth rate is independent of the system size up to the largest simulation we were able to complete. The islands are able to continue growing as long as they merge with each other and maintain a high aspect ratio. Otherwise there is not enough magnetic tension to sustain reconnection. When applied to the sectored magnetic fields in the heliosheath, we show that the islands can continue growing until they reach the sector width and do so in much less time than it takes for the islands to convect through the heliosheath.
We investigate the cosmic evolution of the linear bias in the framework of a flat FLRW spacetime. We consider metric perturbations in the Newtonian gauge, including Hubble scale effects. Making the following assumptions, (i) scale independent current epoch bias $b_0$, (ii) equal accelerations between tracers and matter, (iii) unimportant halo merging effects (which is quite accurate for $z<3$), we analytically derive the scale dependent bias evolution. The identified scale dependence is only due to Hubble scale evolution GR effects, while other scale dependence contributions are ignored. We find that up to galaxy cluster scales the fluctuations of the metric do not introduce a significant scale dependence in the linear bias. Our bias evolution model is then used to derive a connection between the matter growth index $\gamma$ and the observable value of the tracer power spectrum normalization $\sigma_8(z)$. We show how this connection can be used as an observational test of General Relativity on extragalactic scales.
Geometrical cross sections of dust aggregates determine their coupling with disk gas, which governs their motions in protoplanetary disks. Collisional outcomes also depend on geometrical cross sections of initial aggregates. In the previous paper, we performed three-dimensional N-body simulations of sequential collisions of aggregates composed of a number of sub-micron-sized icy particles and examined radii of gyration (and bulk densities) of the obtained aggregates. We showed that collisional compression of aggregates is not efficient and that aggregates remain fluffy. In the present study, we examine geometrical cross sections of the aggregates. Their cross sections decreases due to the compression as well as their gyration radii. It is found that a relation between the cross section and the gyration radius proposed by Okuzumi et al. is valid for the compressed aggregates. We also refine the compression model proposed in our previous paper. The refined model enables us to calculate the evolution of both gyration radii and cross sections of growing aggregates and reproduces well our numerical results of sequential aggregate collisions. The refined model can describe non-equal-mass collisions as well as equal-mass case. Although we do not take into account oblique collisions in the present study, oblique collisions would further hinder compression of aggregates.
Recent radio observations have identified a class of structures, so-called radio relics, in clusters of galaxies. The radio emission from these sources is interpreted as synchrotron radiation from GeV electrons gyrating in microG-level magnetic fields. Radio relics, located mostly in the outskirts of clusters, seem to associate with shock waves, especially those developed during mergers. In fact, they seem to be good structures to identify and probe such shocks in intracluster media (ICMs), provided we understand the electron acceleration and re-acceleration at those shocks. In this paper, we describe time-dependent simulations for diffusive shock acceleration at weak shocks that are expected to be found in ICMs. Freshly injected as well as pre-existing populations of cosmic-ray (CR) electrons are considered, and energy losses via synchrotron and inverse Compton are included. We then compare the synchrotron flux and spectral distributions estimated from the simulations with those in two well-observed radio relics in CIZA J2242.8+5301 and ZwCl0008.8+5215. Considering that the CR electron injection is rather inefficient at weak shocks with Mach number M <~ a few, the existence of radio relics could indicate the pre-existing population of low-energy CR electrons in ICMs. The implication of our results on the merger shock scenario of radio relics is discussed.
We investigate the relation between stellar mass ($M_\star$), star formation rate (SFR), and metallicity of galaxies, so called the fundamental metallicity relation, in the galaxy sample of Sloan Digital Sky Survey Data Release 7. We separate the galaxies into narrow redshift bins and compare the relation at different redshifts, and find statistically significant ($> 99$%) evolution which is not explained solely by the effect of fiber covering fraction. In the current sample of low redshift galaxies, galaxies with different $M_\star$, and SFR are sampled from different redshifts. The separation of the intrinsic relation from the redshift evolution effect is a crucial issue to understand evolution of galaxies.
We used optical images taken with the Very Large Telescope (VLT) in the B and V bands to search for the optical counterpart of PSR J1028-5819 or constrain its optical brightness. At the same time, we used an archival Suzaku observation to confirm the preliminary identification of the pulsar's X-ray counterpart obtained by Swift. Due to the large uncertainty on the pulsar's radio position and the presence of a bright (V = 13.2) early F-type star at < 4", we could not detect its counterpart down to flux limits of B~25.4 and V ~25.3, the deepest obtained so far for PSR J1028-5819. From the Suzaku observations, we found that the X-ray spectrum of the pulsar's candidate counterpart is best-fit by a power-law with spectral index 1.7 +/- 0.2 and an absorption column density NH < 10^21 cm-2, which would support the proposed X-ray identification. Moreover, we found possible evidence for the presence of diffuse emission around the pulsar. If real, and associated with a pulsar wind nebula (PWN), its surface brightness and angular extent would be compatible with the expectations for a ~100 kyr old pulsar at the PSR J1028-5819 distance.
The assumptions that "light propagates along null geodesics of the spacetime metric" and "the number of photons is conserved along the light path" lead to the distance duality relation (DDR), $\eta = D_L(z) (1 + z)^{-2}/D_A(z) = 1$, with $D_L(z)$ and $D_A(z)$ the luminosity and angular diameter distances to a source at redshift $z$. In order to test the DDR, we follow the usual strategy comparing the angular diameter distances of a set of clusters, inferred from X - ray and radio data, with the luminosity distance at the same cluster redshift using the local regression technique to estimate $D_L(z)$ from Type Ia Supernovae (SNeIa) Hubble diagram. In order to both strengthen the constraints on the DDR and get rid of the systematics related to the unknown cluster geometry, we also investigate the possibility to use Baryon Acoustic Oscillations (BAO) to infer $D_A(z)$ from future BAO surveys. As a test case, we consider the proposed Euclid mission investigating the precision can be afforded on $\eta(z)$ from the expected SNeIa and BAO data. We find that the combination of BAO and the local regression coupled allows to reduce the errors on $\eta_a = d\eta/dz|_{z = 0}$ by a factor two if one $\eta_0 = \eta(z = 0) = 1$ is forced and future data are used. On the other hand, although the statistical error on $\eta_0$ is not significantly reduced, the constraints on this quantity will be nevertheless ameliorated thanks to the reduce impact of systematics.
In [Leung et al., Phys. Rev. D 84, 107301 (2011)], we presented our results on using a general relativistic two-fluid formalism to study the hydrostatic equilibrium configuration of an admixture of degenerate dark matter and normal nuclear matter. In this work, we present more analysis to complement our previous findings. We study the radial oscillation modes of these compact stars in detail. We find that these stars in general have two classes of oscillation modes. For a given total mass of the star, the first class of modes is insensitive to the dark-matter particle mass. They also reduce properly to the oscillation modes of the corresponding ordinary neutron star, with the same total mass, when the mass fraction of dark matter tends to zero. On the other hand, the second class of modes is due mainly to the dark-matter fluid. In the small dark-matter mass fraction limit, these modes are characterized purely by the oscillations of dark matter, while the normal matter is essentially at rest. In the intermediate regime where the mass fractions of the two fluids are comparable, the normal matter oscillates with the dark matter due to their coupling through gravity. In contrast to the first class of modes, the frequencies of these dark-matter dominated modes depend sensitively on the mass of dark-matter particles.
Clusters of galaxies, as the largest virialized systems in the Universe, are ideal laboratories to study the formation and evolution of cosmic structures...(abridged)... Most of the detailed knowledge of galaxy clusters has been obtained in recent years from the study of ICM through X-ray Astronomy. At the same time, radio observations have proved that the ICM is mixed with non-thermal components, i.e. highly relativistic particles and large-scale magnetic fields, detected through their synchrotron emission. The knowledge of the properties of these non-thermal ICM components has increased significantly, owing to sensitive radio images and to the development of theoretical models. Diffuse synchrotron radio emission in the central and peripheral cluster regions has been found in many clusters. Moreover large-scale magnetic fields appear to be present in all galaxy clusters, as derived from Rotation Measure (RM) studies. Non-thermal components are linked to the cluster X-ray properties, and to the cluster evolutionary stage, and are crucial for a comprehensive physical description of the intracluster medium. They play an important role in the cluster formation and evolution. We review here the observational properties of diffuse non-thermal sources detected in galaxy clusters: halos, relics and mini-halos. We discuss their classification and properties. We report published results up to date and obtain and discuss statistical properties. We present the properties of large-scale magnetic fields in clusters and in even larger structures: filaments connecting galaxy clusters. We summarize the current models of the origin of these cluster components, and outline the improvements that are expected in this area from future developments thanks to the new generation of radio telescopes.
We observed the ring galaxy NGC 7552 with the mid-infrared (MIR) instrument VISIR at an angular resolution of 0.3"- 0.4" and with the near-infrared (NIR) integral-field spectrograph SINFONI on the VLT, and complement these observations with data from ISO and Spitzer. The starburst ring is clearly detected at MIR wavelengths at the location of the dust-extincted, dark ring seen in HST observations. This "ring", however, is a rather complex annular region of more than 100 parsec width. We find a large fraction of diffuse [Ne II] and PAH emission in the central region that is not associated with the MIR peaks on spatial scales of \sim30 pc. We do not detect MIR emission from the nucleus of NGC 7552, which is very prominent at optical and NIR continuum wavelengths. However, we have identified nine unresolved MIR peaks within the ring. The average extinction of these peaks is A(V)=7.4 and their total infrared luminosity is L(IR) = 2.1*10^10 Lo. The properties of these peaks are typical for MIR-selected massive clusters found in other galaxies. The ages of the MIR-selected clusters are in the range of 5.9\pm0.3 Myr. The age spread among the clusters of 0.8 Myr is small compared to the travel time of \sim5.6 Myr for half an orbit within the starburst ring. We find no strong evidence for a scenario where the continuous inflow of gas leads to the ongoing formation of massive clusters at the contact points between galactic bar and starburst ring. Instead, it appears more likely that the gas density build up more gradually over larger ring segments, and that the local physical conditions govern cluster formation. We note that the fundamental limitation on the accurate derivation of cluster age, mass and IMF slope is the lack of higher angular resolution.
The Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) provides an unprecedented opportunity to search for blazars at sub-mm wavelengths. We cross-matched the FIRST radio source catalogue with the 11655 sources brighter than 35 mJy at 500{\mu}m in the \sim 135 square degrees of the sky covered by the H-ATLAS equatorial fields at 9 h and 15 h, plus half of the field at 12 h. We found that 379 of the H-ATLAS sources have a FIRST counterpart within 10 arcsec, including 8 catalogued blazars (plus one known blazar that was found at the edge of one the H-ATLAS maps). To search for additional blazar candidates we have devised new diagnostic diagrams and found that known blazars occupy a region of the log(S500{\mu}m/S350{\mu}m) vs. log(S500{\mu}m/S1.4GHz) plane separated from that of the other sub-mm sources with radio counterparts. Using this diagnostic we have selected 12 further candidates that turn out to be scattered in the (r-z) vs. (u-r) plane or in the WISE colour-colour diagram proposed by Massaro et al. (2012), where known blazars are concentrated in well defined strips. This suggests that the majority of them either are not blazars or have spectral energy distributions contaminated by their host galaxies. A significant fraction of true blazars are found to be hosted by star-forming galaxies. This finding, supported by an analysis of blazars detected in Planck 545 and 857 GHz bands, is at odds with the notion that blazar hosts are passive ellipticals and indicates that the sub-mm selection is providing a novel prospect on blazar properties. Based on an inspection of the available photometric data, including the WISE all-sky survey, the unpublished VIKING survey and new radio observations, we tentatively estimate that there are 11 blazars with synchrotron flux density S500{\mu}m > 35mJy over the considered area. This result already allows us to constrain blazar evolution models.
Space-based gravitational-wave observatories such as the Laser Interferometer Space Antenna (LISA) use time-shifted and time-scaled linear combinations of differential laser-phase beat signals to cancel the otherwise overwhelming laser frequency noise. Nanosecond timing precision is needed to accurately form these Time-Delay Interferometry (TDI) combinations which defines a ~1 meter requirement on the inter-spacecraft ranging capability. The University of Florida Hardware-in-the-loop LISA Interferometry Simulator (UFLIS) has been used to test Time-Delay Interferometry in a configuration which incorporates variable delays, realistic Doppler shifts, and simulated gravitational-wave signals. The TDI 2.0 combinations are exploited to determine the time-changing delays with nanosecond accuracy using a TDI-ranging reference tone. These variable delays are used in forming the TDI combinations to achieve the LISA interferometry sensitivity resulting from 10 orders of magnitude laser frequency noise cancellation.
We present GMRT 1280 MHz radio continuum observations and follow-up optical studies of the disk and nuclear star formation in a sample of low luminosity bulgeless galaxies. The main aim is to understand bulge formation and overall disk evolution in these late type galaxies. We detected radio continuum from five of the twelve galaxies in our sample; the emission is mainly associated with disk star formation. Only two of the detected galaxies had extended radio emission; the others had patchy disk emission. In the former two galaxies, NGC3445 and NGC4027, the radio continuum is associated with star formation triggered by tidal interactions with nearby companion galaxies. We did follow-up Halpha imaging and nuclear spectroscopy of both galaxies using the Himalayan Chandra Telescope (HCT). The Halpha emission is mainly associated with the strong spiral arms. The nuclear spectra indicate ongoing nuclear star formation in NGC3445 and NGC4027 which maybe associated with nuclear star clusters. No obvious signs of AGN activity were detected. Although nearly bulgeless, both galaxies appear to have central oval distortions in the R band images; these could represent pseudobulges that may later evolve into large bulges. We thus conclude that tidal interactions are an important means of bulge formation and disk evolution in bulgeless galaxies; without such triggers these galaxies appear to be low in star formation and overall disk evolution.
This paper presents a conceptual design for a spectrometer designed specifically for characterizing transiting exoplanets with space-borne infrared telescopes. The design adopting cross-dispersion is intended to be simple, compact, highly stable, and has capability of simultaneous coverage over a wide wavelength region with high throughput. Typical wavelength coverage and spectral resolving power is 1-13 micron with a spectral resolving power of ~ a few hundred, respectively. The baseline design consists of two detectors, two prisms with a dichroic coating and microstructured grating surfaces, and three mirrors. Moving parts are not adopted. The effect of defocusing is evaluated for the case of a simple shift of the detector, and anisotropic defocusing to maintain the spectral resolving power. Variations in the design and its application to planned missions are also discussed.
Eclipses of the hot spot in Z Cha and OY Car observed by many authors during their quiescence are re-analyzed. Distances of the spot from the center of the disk r_s are determined from phases of ingress and egress. In the case of several eclipses of Z Cha and nearly all eclipses of OY Car it is found that r_s(egress) < r_s(ingress). This implies that they are not representative for the radius of the disk r_d and is interpreted as being due to the stream overflow. The r_s(ingress) - dt relations (where dt is the time since last outburst) are improved when points affected by the stream overflow are omitted.
The F-GAMMA program is among the most comprehensive programs that aim at understanding the physics in active galactic nuclei through the multi-frequency monitoring of Fermi blazars. Here we discuss monthly sampled broad-band radio spectra (2.6 - 142 GHz). Two different studies are presented. (a) We discuss that the variability patterns traced can be classified into two classes: (1) to those showing intense spectral-evolution and (2) those showing a self-similar quasi-achromatic behaviour. We show that a simple two-component model can very well reproduce the observed phenomenologies. (b) We present the cm-to-mm behaviour of three gamma-ray bright Narrow Line Seyfert 1 galaxies over time spans varying between ~1.5 and 3 years and compare their variability characteristics with typical blazars.
We present a search for CO emission in a sample of ten type-2 quasar host
galaxies with redshifts of z=0.1-0.4. We detect CO(J=1-0) line emission with
>=5sigma in the velocity integrated intensity maps of five sources. A sixth
source shows a tentative detection at the ~4.5sigma level of its CO(J=1-0) line
emission. The CO emission of all six sources is spatially coincident with the
position at optical, infrared or radio wavelengths. The spectroscopic redshifts
derived from the CO(J=1-0) line are very close to the photometric ones for all
five detections except for the tentative detection for which we find a much
larger discrepancy. We derive gas masses of ~(2-16)x10^9Msun for the CO
emission in the six detected sources, while we constrain the gas masses to
upper limits of Mgas<=8x10^9Msun for the four non-detections. These values are
of the order or slightly lower than those derived for type-1 quasars. The line
profiles of the CO(J=1-0) emission are rather narrow (<=300km/s) and single
peaked, unveiling no typical signatures for current or recent merger activity,
and are comparable to that of type-1 quasars. However, at least one of the
observed sources shows a tidal-tail like emission in the optical that is
indicative for an on-going or past merging event.
We also address the problem of detecting spurious ~5sigma emission peaks
within the field of view.
The CoRoT field LRa02 has been observed with the Berlin Exoplanet Search
Telescope II (BEST II) during the southern summer 2007/2008. A first analysis
of stellar variability led to the publication of 345 newly discovered variable
stars. Now, a deeper analysis of this data set was used to optimize the
variability search procedure. Several methods and parameters have been tested
in order to improve the selection process compared to the widely used J index
for variability ranking. This paper describes an empirical approach to treat
systematic trends in photometric data based upon the analysis of variance
statistics that can significantly decrease the rate of false detections.
Finally, the process of reanalysis and method improvement has virtually
doubled the number of variable stars compared to the first analysis by Kabath
et al. A supplementary catalog of 272 previously unknown periodic variables
plus 52 stars with suspected variability is presented. Improved ephemerides are
given for 19 known variables in the field. In addition, the BEST II results are
compared with CoRoT data and its automatic variability classification.
In this thesis, we use the motion of the Local Group of galaxies (LG) through the Universe to measure the cosmological parameter of non-relativistic matter density, Omega_m. For that purpose, we compare the peculiar velocity of the LG with its gravitational acceleration. The former is known from the dipole of the cosmic microwave background radiation and the latter is estimated here from the clustering dipole of galaxies in the Two Micron All Sky Survey (2MASS) Extended Source Catalog. We start by presenting the general framework of perturbation theory of gravitational instability in the expanding Universe and how it applies to the peculiar motion of the LG. Next, we study a particular effect for the dipole measurement, related to the fact that a nearby Local Void is partially hidden behind our Galaxy. We then describe in detail how we handled the 2MASS extragalactic data for the purpose of our analysis. Finally, we present two methods to estimate the density Omega_m, combined with the linear biasing b into the parameter beta = (Omega_m)^{0.55} / b, from the comparison of the LG velocity and acceleration. The first approach is to study the growth of the 2MASS clustering dipole with increased depth of the sample and compare it with theoretical expectations. The second is to apply the maximum-likelihood method in order to improve the precision of the measurement. With both these methods we find beta=0.4 and Omega_m=0.2, which is consistent with various independent estimates. We also briefly mention some future prospects in the field.
With the goal of understanding why X-rays have been reported near some high velocity clouds, we perform detailed 3 dimensional hydrodynamic and magnetohydrodynamic simulations of clouds interacting with environmental gas like that in the Galaxy's thick disk/halo or the Magellanic Stream. We examine 2 scenarios. In the first, clouds travel fast enough to shock-heat warm environmental gas. In this scenario, the X-ray productivity depends strongly on the speed of the cloud and the radiative cooling rate. In order to shock-heat environmental gas to temperatures of > or = 10^6 K, cloud speeds of > or = 300 km/s are required. If cooling is quenched, then the shock-heated ambient gas is X-ray emissive, producing bright X-rays in the 1/4 keV band and some X-rays in the 3/4 keV band due to O VII and other ions. If, in contrast, the radiative cooling rate is similar to that of collisional ionizational equilibrium plasma with solar abundances, then the shocked gas is only mildly bright and for only about 1 Myr. The predicted count rates for the non-radiative case are bright enough to explain the count rate observed with XMM-Newton toward a Magellanic Stream cloud and some enhancement in the ROSAT 1/4 keV count rate toward Complex C, while the predicted count rates for the fully radiative case are not. In the second scenario, the clouds travel through and mix with hot ambient gas. The mixed zone can contain hot gas, but the hot portion of the mixed gas is not as bright as those from the shock-heating scenario.
The Earth's atmosphere affects ground-based astronomical observations. Scattering, absorption, and radiation processes deteriorate the signal-to-noise ratio of the data received. For scheduling astronomical observations it is, therefore, important to accurately estimate the wavelength-dependent effect of the Earth's atmosphere on the observed flux. In order to increase the accuracy of the exposure time calculator of the European Southern Observatory's (ESO) Very Large Telescope (VLT) at Cerro Paranal, an atmospheric model was developed as part of the Austrian ESO In-Kind contribution. It includes all relevant components, such as scattered moonlight, scattered starlight, zodiacal light, atmospheric thermal radiation and absorption, and non-thermal airglow emission. This paper focuses on atmospheric scattering processes that mostly affect the blue (< 0.55 mum) wavelength regime, and airglow emission lines and continuum that dominate the red (> 0.55 mum) wavelength regime. While the former is mainly investigated by means of radiative transfer models, the intensity and variability of the latter is studied with a sample of 1186 VLT FORS1 spectra. For a set of parameters such as the object altitude angle, Moon-object angular distance, ecliptic latitude, bimonthly period, and solar radio flux, our model predicts atmospheric radiation and transmission at a requested resolution. A comparison of our model with the FORS1 spectra and photometric data for the night-sky brightness from the literature, suggest a model accuracy of about 20%. This is a significant improvement with respect to existing predictive atmospheric models for astronomical exposure time calculators.
During the years 1838-1858, the very massive star {\eta} Carinae became the prototype supernova impostor: it released nearly as much light as a supernova explosion and shed an impressive amount of mass, but survived as a star.1 Based on a light-echo spectrum of that event, Rest et al.2 conclude that "a new physical mechanism" is required to explain it, because the gas outflow appears cooler than theoretical expectations. Here we note that (1) theory predicted a substantially lower temperature than they quoted, and (2) their inferred observational value is quite uncertain. Therefore, analyses so far do not reveal any significant contradiction between the observed spectrum and most previous discussions of the Great Eruption and its physics.
We compute the matter bispectrum in the presence of primordial local non-Gaussianity over a wide range of scales, including the very small nonlinear ones. We use the Halo Model approach, considering non-Gaussian corrections to the halo profiles, the halo mass function and the bias functions. We compare our results in the linear and mildly nonlinear scales to a large ensemble of Gaussian and non-Gaussian numerical simulations. We consider both squeezed and equilateral configurations, at redshift z = 0 and z = 1. For z = 0, the deviations between the Halo Model and the simulations are smaller than 10% in the squeezed limit, both in the Gaussian and non-Gaussian cases. The Halo Model allows to make predictions on scales much smaller than those reached by numerical simulations. For local non-Gaussian initial conditions with a parameter fNL = 100, we find an enhancement of the bispectrum in the squeezed configuration k = k3 = k2 >> k1 \sim 0.01 h^{-1} Mpc, of \sim 15% and \sim 25% on scales k \sim 1 h^{-1} Mpc, at z = 0 and z = 1 respectively. This is mainly due to the non-Gaussian corrections in the linear bias. Finally we provide a very simple expression valid for any scenario, i.e. for any choice of the halo profile, mass and bias functions, which allow for a fast evaluation of the bispectrum on squeezed configurations.
We investigate the anisotropy of stellar winds in binaries to improve the models of accretion in high-mass X-ray binaries. We model numerically the stellar wind from a supergiant component of a binary in radial and three-dimensional radiation hydrodynamic approximation taking into account the Roche potential, Coriolis force, and radiative pressure in the continuum and spectral lines. The Coriolis force influences substantially the mass loss and thus also the accretion rate. The focusing of the stellar wind by the gravitational field of the compact companion leads to the formation of a gaseous tail behind the companion.
We present a study of the effect of High Column Density (HCD) systems on the Lyman \alpha forest correlation function on large scales. We study the effect both numerically, by inserting HCD systems on mock spectra for a specific model, and analytically, in the context of two-point correlations and linear theory. We show that the presence of HCDs substantially contributes to the noise of the correlation function measurement, and systematically alters the measured redshift-space correlation function of the Lyman \alpha forest, increasing the value of the density bias factor and decreasing the redshift distortion parameter $\beta_\alpha$ of the Lyman \alpha forest. We provide simple formulae for corrections on these derived parameters, as a function of the mean effective optical depth and bias factor of the host halos of the HCDs, and discuss the conditions under which these expressions should be valid. In practice, precise corrections to the measured parameters of the Lyman \alpha forest correlation for the HCD effects are more complex than the simple analytical approximations we present, owing to non-linear effects of the damped wings of the HCD systems and the presence of three-point terms. However, we conclude that an accurate correction for these HCD effects can be obtained numerically and calibrated with observations of the HCD-Lyman \alpha cross-correlation. We also discuss an analogous formalism to treat and correct for the contaminating effect of metal lines overlapping the Lyman \alpha forest spectra.
Cold gas streaming along the dark-matter filaments of the cosmic web is predicted to be the major source of fuel for disc buildup, violent disk instability and star formation in massive galaxies at high redshift. We investigate to what extent such cold gas is detectable in the extended circum-galactic environment of galaxies via Ly alpha absorption and selected low ionisation metal absorption lines. We model the expected absorption signatures using high resolution zoom-in AMR cosmological simulations. In the postprocessing, we distinguish between self-shielded gas and unshielded gas. In the self-shielded gas, which is optically thick to Lyman continuum radiation, we assume pure collisional ionisation for species with an ionisation potential greater than 13.6 eV. In the optically thin, unshielded gas these species are also photoionised by the meta-galactic radiation. In addition to absorption of radiation from background quasars, we compute the absorption line profiles of radiation emitted by the galaxy at the centre of the same halo. We predict the strength of the absorption signal for individual galaxies without stacking. We find that the Ly alpha absorption profiles produced by the streams are consistent with observations of absorption and emission Ly alpha profiles in high redshift galaxies. Due to the low metallicities in the streams, and their low covering factors, the metal absorption features are weak and difficult to detect.
We discuss the clustering properties of galaxies with signs of ongoing star formation detected by the Spitzer Space Telescope at 24mum band in the SWIRE Lockman Hole field. The sample of mid-IR-selected galaxies includes ~20,000 objects detected above a flux threshold of S24mum=310muJy. We adopt optical/near-IR color selection criteria to split the sample into the lower-redshift and higher-redshift galaxy populations. We measure the angular correlation function on scales of theta=0.01-3.5 deg, from which, using the Limber inversion along with the redshift distribution established for similarly selected source populations in the GOODS fields (Rodighiero et al. 2010), we obtain comoving correlation lengths of r0=4.98+-0.28 h^-1 Mpc and r0 =8.04+-0.69 h^-1 Mpc for the low-z (<z>=0.7) and high-z (<z>=1.7) subsamples, respectively. Comparing these measurements with the correlation functions of dark matter halos identified in the Bolshoi cosmological simulation (Klypin et al. 2011}, we find that the high-redshift objects reside in progressively more massive halos reaching Mtot>3e12 h^-1 Msun, compared to Mtot>7e11 h^-1 Msun for the low-redshift population. Approximate estimates of the IR luminosities based on the catalogs of 24mum sources in the GOODS fields show that our high-z subsample represents a population of "distant ULIRGs" with LIR>10^12Lsun, while the low-z subsample mainly consists of "LIRGs", LIR~10^11Lsun. The comparison of number density of the 24mum selected galaxies and of dark matter halos with derived minimum mass Mtot shows that only 20% of such halos may host star-forming galaxies.
We present an Advanced Camera for Surveys/ Solar Blind Channel far-ultraviolet (FUV) study of \h2 gas in 12 weak T Tauri stars in nearby star-forming regions. The sample consists of sources which have no evidence of inner disk dust. Our new FUV spectra show that in addition to the dust, the gas is depleted from the inner disk. This sample is combined with a larger FUV sample of accretors and non-accretors with ages between 1 and 100 Myr, showing that as early as 1--3 Myr, systems both with and without gas are found. Possible mechanisms for depleting gas quickly include viscous evolution, planet formation and photoevaporation by stellar radiation fields. Since these mechanisms alone cannot account for the lack of gas at 1--3 Myr, it is likely that the initial conditions (e.g. initial disk mass or core angular momentum) contribute to the variety of disks observed at any age. We estimate the angular momentum of a cloud needed for most of the mass to fall very close to the central object and compare this to models of the expected distribution of angular momenta. Up to 20% of cloud cores have low enough angular momenta to form disks with the mass close to the star, which would then accrete quickly; this percentage is similar to the fraction of diskless stars in the youngest star forming regions. With our sample, we characterize the chromospheric contribution to the FUV luminosity and find that $L_{FUV}/L_{bol}$ saturates at $\sim10^{-4.1}$.
Recent infrared (IR) observations of freshly-formed dust in supernova remnants (SNRs) have yielded significantly lower dust masses than predicted by theoretical models and measured from high redshift observations. The Crab Nebula's pulsar wind is thought to be sweeping up freshly-formed supernova (SN) dust along with the ejected gas. The evidence for this dust was found in the form of an IR excess in the integrated spectrum of the Crab and in extinction against the synchrotron nebula that revealed the presence of dust in the filament cores. We present the first spatially resolved emission spectra of dust in the Crab Nebula acquired with the Infrared Spectrograph aboard the Spitzer Space Telescope. The IR spectra are dominated by synchrotron emission and show forbidden line emission from from S, Si, Ne, Ar, O, Fe, and Ni. We derived a synchrotron spectral map from the 3.6 and 4.5 microns images, and subtracted this contribution from our data to produce a map of the residual continuum emission from dust. The dust emission appears to be concentrated along the ejecta filaments and is well described by an amorphous carbon or silicate grain compositions. We find a dust temperature of 55+/- 4 K for silicates and 60 +/- 7 K for carbon grains. The total estimated dust mass is 0.0012-0.012 solar masses, well below the theoretical dust yield predicted for a core-collapse supernova. Our grain heating model implies that the dust grain radii are relatively small, unlike what is expected for dust grains formed in a Type IIP SN.
This review outlines concepts of mathematical statistics, elements of probability theory, hypothesis tests and point estimation for use in the analysis of modern astronomical data. Least squares, maximum likelihood, and Bayesian approaches to statistical inference are treated. Resampling methods, particularly the bootstrap, provide valuable procedures when distributions functions of statistics are not known. Several approaches to model selection and good- ness of fit are considered. Applied statistics relevant to astronomical research are briefly discussed: nonparametric methods for use when little is known about the behavior of the astronomical populations or processes; data smoothing with kernel density estimation and nonparametric regression; unsupervised clustering and supervised classification procedures for multivariate problems; survival analysis for astronomical datasets with nondetections; time- and frequency-domain times series analysis for light curves; and spatial statistics to interpret the spatial distributions of points in low dimensions. Two types of resources are presented: about 40 recommended texts and monographs in various fields of statistics, and the public domain R software system for statistical analysis. Together with its \sim 3500 (and growing) add-on CRAN packages, R implements a vast range of statistical procedures in a coherent high-level language with advanced graphics.
Long-lived, stable jets are observed in a wide variety of systems, from protostars, through Galactic compact objects to active galactic nuclei (AGN). Magnetic fields play a central role in launching, accelerating, and collimating the jets through various media. The termination of jets in molecular clouds or the interstellar medium deposits enormous amounts of mechanical energy and momentum, and their interactions with the external medium, as well, in many cases, as the radiation processes by which they are observed, are intimately connected with the magnetic fields they carry. This review focuses on the properties and structures of magnetic fields in long-lived jets, from their launch from rotating magnetized young stars, black holes, and their accretion discs, to termination and beyond. We compare the results of theory, numerical simulations, and observations of these diverse systems and address similarities and differences between relativistic and non-relativistic jets in protostellar versus AGN systems. On the observational side, we focus primarily on jets driven by AGN because of the strong observational constraints on their magnetic field properties, and we discuss the links between the physics of these jets on all scales.
Context. The gamma-ray binary LS 5039 and the isolated pulsar PSR J1825-1446 were proposed to have been formed in the supernova remnant (SNR) G016.8-01.1. Aims. We aim to obtain the Galactic trajectory of LS 5039 and PSR J1825-1446 to find their origin in the Galaxy, and in particular to check their association with SNR G016.8-01.1 to restrict their age. Methods. By means of radio and optical observations we obtained the proper motion and the space velocity of the sources. Results. The proper motion of PSR J1825-1446 corresponds to a transverse space velocity of 690 km/s at a distance of 5 kpc. Its Galactic velocity at different distances is not compatible with the expected Galactic rotation. The velocity and characteristic age of PSR J1825-1446 make it incompatible with SNR G016.8-01.1. There are no clear OB associations or SNRs crossing the past trajectory of PSR J1825-1446. We estimate the age of the pulsar to be 80-245 kyr, which is compatible with its characteristic age. The proper motion of LS 5039 is 7.09 and -8.82 mas/yr in right ascension and declination, respectively. The association of LS 5039 with SNR G016.8-01.1 is unlikely, although we cannot to discard it. The system would have had to be formed in the association Ser OB2 (at 2.0 kpc) if the age of the system is 1.0-1.2 Myr, or in the association Sct OB3 (distance 1.5-2 kpc) for an age of 0.1-0.2 Myr. If the system were not formed close to Ser OB2, the pseudo-synchronization of the orbit would be unlikely. Conclusions. PSR J1825-1446 is a high-velocity isolated pulsar ejected from the Galaxy. The distance to LS 5039, which needs to be constrained by future astrometric missions such as Gaia, is a key parameter for restricting its origin and age.
We study the growth of black holes (BHs) in galaxies using three-dimensional smoothed particle hydrodynamic (SPH) simulations with new implementations of the momentum mechanical feedback, and restriction of accreted elements to those that are gravitationally bound to the BH. We also include the feedback from the X-ray radiation emitted bythe black hole, which heats the surrounding gas in the host galaxies, and adds radial momentum to the fluid. We perform simulations of isolated galaxies and merging galaxies and test various feedback models with the new treatment of the Bondi radius criterion. We find that overall the black hole growth is similar to what has been obtained by earlier workers using the Springel, Di Matteo, & Hernquist algorithms. However, the outflowing wind velocities and mechanical energy emitted by winds are considerably higher (v_w ~ 1000-3000 km/s) compared to the standard thermal feedback model (v_w ~ 50-100 km/s). While the thermal feedback model emits only 0.1 % of BH released energy in winds, the momentum feedback model emits more than 30 % of the total energy released by the BH in winds. In the momentum feedback model, the degree of fluctuation in both radiant and wind output is considerably larger than in the standard treatments. We check that the new model of the BH mass accretion agrees with analytic results for the standard Bondi problem.
We discuss on the possibility that colliding dark matter particles in the form of neutralinos may be gravitationally boosted near the super-massive black hole at the galactic center so that they can have enough collision energy to annihilate into a stau pair. Since in some phenomenologically favored supersymmetric models the mass splitting between the neutralino and the lightest stau, one of the two scalar superpartners of the tau lepton, is a few GeVs, this channel may be allowed. In addition, staus can only decay into a tau lepton and another neutralino. We calculate the gamma-ray spectrum and flux generated by the tau pair discussing the observability of the obtained features.
In this topical review we discuss the connections between chaos, decoherence and quantum cosmology. We understand chaos as classical chaos in systems with a finite number of degrees of freedom, decoherence as environment induced decoherence and quantum cosmology as the theory of the Wheeler - DeWitt equation or else the consistent history formulation thereof, first in mini super spaces and later through its extension to midi super spaces. The overall conclusion is that consideration of decoherence is necessary (and probably sufficient) to sustain an interpretation of quantum cosmology based on the Wave function of the Universe adopting a Wentzel - Kramers - Brillouin form for large Universes, but a definitive account of the semiclassical transition in classically chaotic cosmological models is not available in the literature yet.
The instability of rotating Kerr black holes due to massive scalar perturbations is investigated. It is well known that a bosonic field impinging on a Kerr black hole can be amplified as it scatters off the hole. This superradiant scattering occurs for frequencies in the range $\omega<m\Omega$, where $\Omega$ is the angular frequency of the black hole and $m$ is the azimuthal harmonic index of the mode. If the incident field has a non-zero rest mass, $\mu$, then the mass term effectively works as a mirror, reflecting the scattered wave back towards the black hole. The wave may bounce back and forth between the black hole and some turning point amplifying itself each time. This may lead to a dynamical instability of the system, a phenomena known as a "black-hole bomb". In this work we provide a bound on the instability regime of rotating Kerr spacetimes. In particular, we show that Kerr black holes are stable to massive perturbations in the regime $\mu\geq\sqrt{2}m\Omega$.
We present data from electron-positron pair production by an ultra-intense laser incident on solid Au targets with thickness between 1 and 4 mm. The experiment was performed at the Texas Petawatt Laser in July 2011, with intensities on the order of several x1019W.cm-2 and laser energies around 50 J. We discuss the design of an electron-positron magnetic spectrometer to record the lepton energy spectra ejected from the Au targets. We then present a deconvolution algorithm to extract the lepton energy spectra. We measured hot electron spectra out to > 50MeV, which show a narrow peak around 10 - 15 MeV, plus exponential tail consistent with ponderomotive temperature scaling. We did not observe direct evidence of positron production above the background, even though separate gamma-ray measurement hints at the presence of positrons.
We have found that the relation between the flow through campylotic (generically curved) media, consisting of randomly located curvature perturbations, and the average Ricci scalar of the system exhibits two distinct functional expressions (hysteresis), depending on whether the typical spatial extent of the curvature perturbation lies above or below the critical value maximizing the overall Ricci curvature. Furthermore, the flow through such systems as a function of the number of curvature perturbations presents a sublinear behavior for large concentrations due to the interference between curvature perturbations that, consequently, produces a less curved space. For the purpose of this study, we have developed and validated a lattice kinetic model capable of describing fluid flow in arbitrarily curved manifolds, which allows to deal with highly complex spaces in a very compact and efficient way.
The kinetic decoupling of dark matter (DM) from the primordial plasma sets the size of the first and smallest dark matter halos. Studies of the DM kinetic decoupling have hitherto mostly neglected interactions between the DM and the quarks in the plasma. Here we illustrate their importance using two frameworks: a version of the Minimal Supersymmetric Standard Model (MSSM) and an effective field theory with effective DM-quark interaction operators. We connect particle physics and astrophysics obtaining bounds on the smallest dark matter halo size from collider data and from direct dark matter search experiments. In the MSSM framework, adding DM-quark interactions to DM-lepton interactions more than doubles the smallest dark matter halo mass in a wide range of the supersymmetric parameter space.
We consider the lightest supersymmetric particle (LSP), neutralino in minimal anomaly mediated supersymmetry breaking model (mAMSB) to be a possible candidate for weakly interacting massive particles (WIMP) or cold dark matter and investigate its direct and indirect detections. The supersymmetric parametric space for such a model is constrained by the WMAP results for relic densities. The spin independent and spin dependent scattering cross sections for dark matter off nucleon are thus constrained from the WMAP results. They are found to be within the allowed regions of different ongoing direct detection experiments. The annihilation of such dark matter candidates at the galactic centre produce different standard model particles such as gamma rays, neutrinos etc. In this work, we investigate the possible fluxes of such particles from galactic centre. The neutrino flux from the galactic centre and at different locations away from the galactic centre produced by WIMP annihilation in this model are also obtained for four types of dark matter halo profile. The possibility of detection of such neutrinos from galactic centre at the ANTARES under sea neutrino detector is also investigated. We have studied signals from dark matter annihilations from different angles of observations for different spherically symmetric dark matter halo distribution models in the galaxy. We have compared our gamma ray flux results for four different halo models with the HESS experimental data.
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We study the effect of the supersonic baryon--CDM flow, which has recently been shown to have a large effect on structure formation during the dark ages 10 <~ z <~ 1000, on the abundance of luminous, low-mass satellite galaxies around galaxies like the Milky Way. As the supersonic baryon--CDM flow significantly suppresses both the number of halos formed and the amount of baryons accreted onto such halos of masses 10^6 < M_{halo} / M_solar < 10^8 at z >~ 10, a large effect results on the stellar luminosity function before reionization. As halos of these masses are believed to have very little star formation after reionization due to the effects of photo-heating by the ultraviolet background, this effect persists to the present day. We calculate that the number of low-mass 10^6 < M_{halo} / M_solar < 10^8 halos that host luminous satellite galaxies today is typically suppressed by 50 percent, with values ranging up to 90 percent in regions where the initial supersonic velocity is high. We show that this previously-ignored cosmological effect resolves most of the tension between the observed and predicted number of low-mass satellites in the Milky Way, obviating the need for any other mass-dependent star-formation suppression before reionization.
We report the discovery of a brown dwarf companion to the young M dwarf 1RXS J235133.3+312720 as part of a high contrast imaging search for planets around nearby young low-mass stars with Keck-II/NIRC2 and Subaru/HiCIAO. The 2.4" (~120 AU) pair is confirmed to be comoving from two epochs of high resolution imaging. Follow-up low- and moderate-resolution near-infrared spectroscopy of 1RXS J2351+3127 B with IRTF/SpeX and Keck-II/OSIRIS reveals a spectral type of L0$^{+2}_{-1}$. The M2 primary star 1RXS J2351+3127 A exhibits X-ray and UV activity levels comparable to young moving group members with ages of ~10-100 Myr. UVW kinematics based the measured radial velocity of the primary and the system's photometric distance (50 +/- 10 pc) indicate it is likely a member of the ~50-150 Myr AB Dor moving group. The near-infrared spectrum of 1RXS J2351+3127 B does not exhibit obvious signs of youth, but its H-band morphology shows subtle hints of intermediate surface gravity. The spectrum is also an excellent match to the ~200 Myr M9 brown dwarf LP 944-20. Assuming an age of 50-150 Myr, evolutionary models imply a mass of 32 +/- 6 Mjup for the companion, making 1RXS J2351+3127 B the second lowest-mass member of the AB Dor moving group after the L4 companion CD-35 2722 B and one of the few benchmark brown dwarfs known at young ages.
In later papers we have shown that sunward, generally dark, plasma features originated above posteruption flare arcades are consistent with a scenario where plasma voids are generated by the bouncing and interfering of shocks and expansion waves upstream of an initial localized deposition of energy which is collimated in the magnetic field direction. In this paper we analyze the multiple production and interaction of supra--arcade downflows (SAD) and the structure of individual SADs that make them relatively stable features while moving. We compare our results with observations and with the scenarios proposed by other authors.
We present new radial velocities for 289 globular clusters around NGC 4636, the southernmost giant elliptical galaxy of the Virgo cluster. The data were obtained with FORS2/MXU at the Very Large Telescope. Together with data analysed in an earlier study (Schuberth et al. 2006), we now have a sample of 460 globular cluster velocities out to a radius of 12 arcmin (60 kpc) available - one of the largest of its kind. This new data set also provides a much more complete angular coverage. Moreover, we present new kinematical data of the inner stellar population of NGC 4636. We perform an updated Jeans analysis, using both stellar and GC data, to better constrain the dark halo properties. We find a stellar M/L-ratio of 5.8 in the R-band, higher than expected from single stellar population synthesis. We model the dark halo by cored and cuspy analytical halo profiles and consider different anisotropies for the tracer populations. Properties of NFW halos lie well within the expected range of cosmological simulations. Cored halos give central dark matter densities, which are typical for elliptical galaxies of NGC 4636's luminosity. The surface densities of the dark matter halos are higher than those of spiral galaxies. We compare the predictions of Modified Newtonian Dynamics with the derived halo properties and find satisfactory agreement. Therefore NGC 4636 therefore falls onto the baryonic Tully-Fisher relation for spiral galaxies. The comparison with the X-ray mass profile of Johnson et al. (2009) reveals satisfactory agreement only, if the abundance gradient of hot plasma has been taken into account. This might indicate a general bias towards higher masses for X-ray based mass profiles in all systems, including galaxy clusters, with strong abundance gradients.
We present an analysis of the structures and dynamics of the merging cluster Abell~1201, which has two sloshing cold fronts around a cooling core, and an offset gas core approximately 500kpc northwest of the center. New Chandra and XMM-Newton data reveal a region of enhanced brightness east of the offset core, with breaks in surface brightness along its boundary to the north and east. This is interpreted as a tail of gas stripped from the offset core. Gas in the offset core and the tail is distinguished from other gas at the same distance from the cluster center chiefly by having higher density, hence lower entropy. In addition, the offset core shows marginally lower temperature and metallicity than the surrounding area. The metallicity in the cool core is high and there is an abrupt drop in metallicity across the southern cold front. We interpret the observed properties of the system, including the placement of the cold fronts, the offset core and its tail in terms of a simple merger scenario. The offset core is the remnant of a merging subcluster, which first passed pericenter southeast of the center of the primary cluster and is now close to its second pericenter passage, moving at ~1000 km/s. Sloshing excited by the merger gave rise to the two cold fronts and the disposition of the cold fronts reveals that we view the merger from close to the plane of the orbit of the offset core.
The Auger Engineering Radio Array (AERA) is currently detecting cosmic rays of energies at and above 10^17 eV at the Pierre Auger Observatory, by triggering on the radio emission produced in the associated air showers. The radio-detection technique must cope with a significant background of man-made radio-frequency interference, but can provide information on shower development with a high duty cycle. We discuss our techniques to handle the challenges of self-triggered radio detection in a low-power autonomous array, including triggering and filtering algorithms, data acquisition design, and communication systems.
Mechanisms regulating the origin of X-rays in YSOs and the correlation with their evolutionary stage are under debate. Studies of the X-ray properties in young clusters allow to understand these mechanisms. One ideal target for this analysis is the Eagle Nebula (M16), with its central cluster NGC6611. At 1750 pc from the Sun, it harbors 93 OB stars, together with a population of low-mass stars from embedded protostars to disk-less Class III objects, with age <= 3Myrs. We study an archival 78 ksec Chandra/ACIS-I observation of NGC6611, and two new 80ksec observations of the outer region of M16, one centered on the Column V, and one on a region of the molecular cloud with ongoing star-formation. We detect 1755 point sources, with 1183 candidate cluster members (219 disk-bearing and 964 disk-less). We study the global X-ray properties of M16 and compare them with those of the Orion Nebula Cluster. We also compare the level of X-ray emission of Class II and Class III stars, and analyze the X-ray spectral properties of OB stars. Our study supports the lower level of X-ray activity for the disk-bearing stars with respect to the disk-less members. The X-ray Luminosity Function (XLF) of M16 is similar to that of Orion, supporting the universality of the XLF in young clusters. 85% of the O stars of NGC6611 have been detected in X-rays. With only one possible exception, they show soft spectra with no hard component, indicating that mechanisms for the production of hard X-ray emission in O stars are not operating in NGC 6611.
The sudden reconnection of a non-force free 2D current layer, embedded in a low-beta plasma, triggered by the onset of an anomalous resistivity, is studied in detail. The resulting behaviour consists of two main phases. Firstly, a transient reconnection phase, in which the current in the layer is rapidly dispersed and some flux is reconnected. This dispersal of current launches a family of small amplitude magnetic and plasma perturbations, which propagate away from the null at the local fast and slow magnetosonic speeds. The vast majority of the magnetic energy released in this phase goes into internal energy of the plasma, and only a tiny amount is converted into kinetic energy. In the wake of the outwards propagating pulses, an imbalance of Lorentz and pressure forces creates a stagnation flow which drives a regime of impulsive bursty reconnection, in which fast reconnection is turned on and off in a turbulent manner as the current density exceeds and falls below a critical value. During this phase, the null current density is continuously built up above a certain critical level, then dissipated very rapidly, and built up again, in a stochastic manner. Interestingly, the magnetic energy converted during this quasi-steady phase is greater than that converted during the initial transient reconnection phase. Again essentially all the energy converted during this phase goes directly to internal energy. These results are of potential importance for solar flares and coronal heating, and set a conceptually important reference for future 3D studies.
We present the discovery of another seven Y dwarfs from the Wide-field Infrared Survey Explorer (WISE). Using these objects, as well as the first six WISE Y dwarf discoveries from Cushing et al., we further explore the transition between spectral types T and Y. We find that the T/Y boundary roughly coincides with the spot where the J-H colors of brown dwarfs, as predicted by models, turn back to the red. Moreover, we use preliminary trigonometric parallax measurements to show that the T/Y boundary may also correspond to the point at which the absolute H (1.6 um) and W2 (4.6 um) magnitudes plummet. We use these discoveries and their preliminary distances to place them in the larger context of the Solar Neighborhood. We present a table that updates the entire stellar and substellar constituency within 8 parsecs of the Sun, and we show that the current census has hydrogen-burning stars outnumbering brown dwarfs by roughly a factor of six. This factor will decrease with time as more brown dwarfs are identified within this volume, but unless there is a vast reservoir of cold brown dwarfs invisible to WISE, the final space density of brown dwarfs is still expected to fall well below that of stars. We also use these new Y dwarf discoveries, along with newly discovered T dwarfs from WISE, to investigate the field substellar mass function. We find that the overall space density of late-T and early-Y dwarfs matches that from simulations describing the mass function as a power law with slope -0.5 < alpha < 0.0; however, a power-law may provide a poor fit to the observed object counts as a function of spectral type because there are tantalizing hints that the number of brown dwarfs continues to rise from late-T to early-Y. More detailed monitoring and characterization of these Y dwarfs, along with dedicated searches aimed at identifying more examples, are certainly required.
In this paper, the holographic dark energy (HDE) model, where the future event horizon is taken as an IR cut-off, is confronted by using currently available cosmic observational data sets which include type Ia supernovae, baryon acoustic oscillation and cosmic microwave background radiation from full information of WMAP-7yr. Via the Markov Chain Monte Carlo method, we obtain the values of model parameter $c= 0.696_{- 0.0737- 0.132- 0.190}^{+ 0.0736+ 0.159+ 0.264}$ with $1,2,3\sigma$ regions. Therefore one can conclude that at lest $3\sigma$ level the future Universe will be dominated by phantom like dark energy. It is not consistent with positive energy condition, however this condition must be satisfied to derive the holographic bound. It implies that the current cosmic observational data points disfavor the HDE model.
The subject of this paper is stochastic acceleration by plasma turbulence, a process akin to the original model proposed by Fermi. We review the relative merits of different acceleration models, in particular the so called first order Fermi acceleration by shocks and second order Fermi by stochastic processes, and point out that plasma waves or turbulence play an important role in all mechanisms of acceleration. Thus, stochastic acceleration by turbulence is active in most situations. We also show that it is the most efficient mechanism of acceleration of relatively cool non relativistic thermal background plasma particles. In addition, it can preferentially accelerate electrons relative to protons as is needed in many astrophysical radiating sources, where usually there are no indications of presence of shocks. We also point out that a hybrid acceleration mechanism consisting of initial acceleration by turbulence of background particles followed by a second stage acceleration by a shock has many attractive features. It is demonstrated that the above scenarios can account for many signatures of the accelerated electrons, protons and other ions, in particular $^3$He and $^4$He, seen directly as Solar Energetic Particles and through the radiation they produce in solar flares.
We study the observational signature of vector metric perturbations through the effect of weak gravitational lensing. In the presence of vector perturbations, the non-vanishing signals for B-mode cosmic shear and curl-mode deflection angle, which have never appeared in the case of scalar metric perturbations, naturally arise. Solving the geodesic and geodesic deviation equations, we drive the full-sky formulas for angular power spectra of weak lensing signals, and give the explicit expressions for E-/B-mode cosmic shear and gradient-/curl-mode deflection angle. As a possible source for seeding vector perturbations, we then consider a cosmic string network, and discuss its detectability from upcoming weak lensing and CMB measurements. Based on the formulas and a simple model for cosmic string network, we calculate the angular power spectra and expected signal-to-noise ratios for the B-mode cosmic shear and curl-mode deflection angle. We find that the weak lensing signals are enhanced for a smaller intercommuting probability of the string network, $P$, and they are potentially detectable from the upcoming cosmic shear and CMB lensing observations. For $P\sim 10^{-1}$, the minimum detectable tension of the cosmic string will be down to $G\mu\sim 5\times 10^{-8}$. With a theoretically inferred smallest value $P\sim 10^{-3}$, we could even detect the string with $G\mu\sim 5\times 10^{-10}$.
We present the production cross-section of gamma-rays based on data of p-p collisions at LHC, revising the previous semi-empirical formula mainly for 1) the inelastic cross-section in p-p collisions, $\sigma_{\scriptsize {pp}}(E_0)$, and 2) the inclusive $\gamma$-ray spectrum in the forward region, $\sigma_{pp \rightarrow \gamma}(E_0, E_\gamma)$. We find that the previous cross-section gives a significantly softer spectrum than found in the data of LHC. In this paper, we focus our interest mainly upon the LHC forward (LHCf) experiment, giving gamma-ray spectra in the very forward region with the pseudo-rapidity $\eta^*$\,$\gsim$\,8.8 in the center of mass system (CMS), which have not been reported so far. We also give the pseudo-rapidity distribution of charged hadrons with $-3 \le \eta^* \le 3$ obtained by ALICE and TOTEM experiments, both with LHC. We find that the revised cross-section reproduces quite well the accelerator data over the wide energy range from GeV to 30 PeV for projectile protons, corresponding approximately to 100 MeV to 3 PeV for secondary gamma-rays. The production cross-section of gamma-rays produced in the forward region is essential for the study of gamma-ray astronomy, while not important are those produced in the central region in CMS, and of much less importance in the backward. We discuss also the average transverse momentum of gamma-rays, $\bar{p}_{t}$, and the average inelasticity transferred to gamma-rays, $\bar{k}_\gamma^*$, obtaining that the former increases very slowly with $\bar{p}_{t} = 100 \sim 220$\,MeV/c for $E_0 = 1\,{GeV} \sim 26\,{PeV}$, and the latter is almost independent of $E_0$, with $\bar{k}_\gamma^* \approx 1/6,$ while we can not exclude the possibility of a small increase of $\bar{k}_\gamma^*$.
PSR B1259-63/LS 2883 is a binary system in which a 48-ms pulsar orbits around a Be star in a high eccentric orbit with a long orbital period of about 3.4 yr. It is special for having asymmetric two-peak profiles in both the X-ray and the TeV light curves. Recently, an unexpected GeV flare was detected by $Fermi$ gamma-ray observatory several weeks after the last periastron passage. In this paper, we show that this observed GeV flare could be produced by the Doppler-boosted synchrotron emission in the bow shock tail. An anisotropic pulsar wind model, which mainly affects the energy flux injection to the termination shock in different orbital phase, is also used in this paper, and we find that the anisotropy in the pulsar wind can play a significant role in producing the asymmetric two-peak profiles in both X-ray and TeV light curves. The X-ray and TeV photons before periastron are mainly produced by the shocked electrons around the shock apex and the light curves after periastron are contributed by the emission from the shock apex and the shock tail together, which result in the asymmetric two-peak light curves.
We report that the optical polarization in the afterglow of GRB 091208B is measured at t = 149 - 706 s after the burst trigger, and the polarization degree is P = 10.4% +/- 2.5%. The optical light curve at this time shows a power-law decay with index -0.75 +/- 0.02, which is interpreted as the forward shock synchrotron emission, and thus this is the first detection of the early-time optical polarization in the forward shock (rather than that in the reverse shock reported by Steele et al. (2009). This detection disfavors the afterglow model in which the magnetic fields in the emission region are random on the plasma skin depth scales, such as amplified by the plasma instabilities, e.g., Weibel instability. We suggest that the fields are amplified by the magnetohydrodynamic instabilities, which would be tested by future observations of the temporal changes of the polarization degrees and angles for other bursts.
We searched a short-term radio variability in an active galactic nucleus PKS 1510-089. A daily flux monitoring for 143 days at 8.4 GHz was performed, and VLBI observations at 8.4, 22, and 43 GHz were carried out 4 times during the flux monitoring period. As a result, variability with time scale of 20 to 30 days was detected. The variation patterns were well alike on three frequencies, moreover those at 22 and 43 GHz were synchronized. These properties support that this short-term variability is an intrinsic one. The Doppler factor estimated from the variability time scale is 47. Since the Doppler factor is not extraordinary large for AGN, such intrinsic variability with time scale less than 30 days would exist in other AGNs.
We have been monitoring yearly variation in the Sun's polar magnetic fields with the Solar Optical Telescope aboard {\it Hinode} to record their evolution and expected reversal near the solar maximum. All magnetic patches in the magnetic flux maps are automatically identified to obtain the number density and magnetic flux density as a function of th total magnetic flux per patch. The detected magnetic flux per patch ranges over four orders of magnitude ($10^{15}$ -- $10^{20}$ Mx). The higher end of the magnetic flux in the polar regions is about one order of magnitude larger than that of the quiet Sun, and nearly that of pores. Almost all large patches ($ \geq 10^{18}$ Mx) have the same polarity, while smaller patches have a fair balance of both polarities. The polarity of the polar region as a whole is consequently determined only by the large magnetic concentrations. A clear decrease in the net flux of the polar region is detected in the slow rising phase of the current solar cycle. The decrease is more rapid in the north polar region than in the south. The decrease in the net flux is caused by a decrease in the number and size of the large flux concentrations as well as the appearance of patches with opposite polarity at lower latitudes. In contrast, we do not see temporal change in the magnetic flux associated with the smaller patches ($ < 10^{18}$ Mx) and that of the horizontal magnetic fields during the years 2008--2012.
On the final day of the Stellar Polarimetry conference, participants split up into three "breakout sessions" to discuss the future of the field in the areas of instrumentation, upcoming opportunities, and community priorities. This contribution compiles the major recommendations arising from each breakout session. We hope that the polarimetric community will find these ideas useful as we consider how to maintain the vitality of polarimetry in the coming years.
The ANTARES detector is the most sensitive neutrino telescope observing the southern sky and the world's first particle detector operating in the deep sea. It is installed in the Mediterranean Sea at a depth of 2475 m. As an example of early results, the determination of the atmospheric muon flux is discussed and a good agreement with previous measurements is found. Furthermore, the results of a search for high-energy events in excess of the atmospheric neutrino flux are reported and significant limits are set on the diffuse cosmic neutrino flux in the multi-TeV to PeV energy range. Using data from more than 800 days of effective data taking, partly during the construction phase, a first analysis searching for point-like excesses in the neutrino sky distribution has been performed. The resulting sensitivity of ANTARES is reported and compared to measurements of other detectors. A method employed for a first search for neutrinos from Fermi-detected gamma-ray flaring blazars in the last 4 months of 2008 is described and the results are reported. No significant neutrino signal in excess of that expected from atmospheric background has been found.
{Abridged version for ArXiv}. We provide direct constraints on the origin of the [Ne II] emission in 15 young stars using high-spatial and spectral resolution observations with VISIR at the VLT that allow us to study the kinematics of the emitting gas. In addition we compare the [Ne II] line with optical forbidden lines observed for three stars with UVES. The [Ne II] line was detected in 7 stars, among them the first confirmed detection of [Ne II] in a Herbig Be star, V892 Tau. In four cases, the large blueshifted lines indicate an origin in a jet. In two stars, the small shifts and asymmetric profiles indicate an origin in a photo-evaporative wind. CoKu Tau 1, seen close to edge-on, shows a spatially unresolved line centered at the stellar rest velocity, although cross-dispersion centroids move within 10 AU from one side of the star to the other as a function of wavelength. The line profile is symmetric with wings extending up to about +-80 km/s. The origin of the [Ne II] line could either be due to the bipolar jet or to the disk. For the stars with VLT-UVES observations, in several cases, the optical forbidden line profiles and shifts are very similar to the profile of the [Ne II] line, suggesting that the lines are emitted in the same region. A general trend observed with VISIR is a lower line flux when compared with the fluxes obtained with Spitzer. We found no correlation between the line full-width at half maximum and the line peak velocity. The [Ne II] line remains undetected in a large part of the sample, an indication that the emission detected with Spitzer in those stars is likely extended.
We present results of AO-assisted K-band IFU spectroscopy of the massive young star IRAS13481-6124 performed with ESO's VLT/SINFONI instrument. Our spectro-astrometric analysis of the Br{\gamma} line revealed a photo-center shift with respect to the adjacent continuum of \sim1 AU at a distance of 3.1 kpc. The position angle of this shift matches with that of the outflow which confirms that the massive star is indeed the driving source. Furthermore, a velocity gradient along the major disk axis was found which hints at the rotational sense of the ionized region, and thus of the disk as well. The gradient is not consistent with Keplerian motion but points to rigid rotation of the innermost disk. Notably, emission of H_2 is absent from source while both shocked and fluorescent H_2 emission are observed in its immediate surroundings.
The population of Neptune Trojans is believed to be bigger than that of Jupiter Trojans and that of asteroids in the main belt, although only eight members of this far distant asteroid swarm have been observed up to now. Six leading Neptune Trojans around the Lagrange point L4 discovered earlier have been studied in detail, but two trailing ones found recently around the L5 point, 2004 KV18 and 2008 LC18, have not been investigated yet. In this paper, we report our investigations on the dynamical behaviors of these two new Neptune Trojans. Our calculations show that the asteroid 2004 KV18 is a temporary Neptune Trojan. Most probably, it was captured into the trailing Trojan cloud no earlier than 203kyr ago, and it will not keep this identity no later than 165kyr in future. Based on the statistics on our orbital simulations, we argue that this object is more like a scattered Kuiper belt object. On the contrary, the orbit of asteroid 2008 LC18 is much more stable. Among the clone orbits spread within the orbital uncertainties, a considerable portion of clones may survive on the L5 tadpole orbits for 4Gyr. The strong dependence of the stability on the semimajor axis and resonant angle suggests that further observations are badly needed to confine the orbit in the stable region. We also discuss the implications of the existence and dynamics of these two trailing Trojans on the Solar system history.
In this review we confront the current theoretical understanding of particle acceleration at relativistic outflows with recent observational results on various source classes thought to involve such outflows, e.g. gamma-ray bursts, active galactic nuclei, and pulsar wind nebulae. We highlight the possible contributions of these sources to ultra-high-energy cosmic rays.
We present the results of a search for gravitational waves associated with 154 gamma-ray bursts (GRBs) that were detected by satellite-based gamma-ray experiments in 2009-2010, during the sixth LIGO science run and the second and third Virgo science runs. We perform two distinct searches: a modeled search for coalescences of either two neutron stars or a neutron star and black hole; and a search for generic, unmodeled gravitational-wave bursts. We find no evidence for gravitational-wave counterparts, either with any individual GRB in this sample or with the population as a whole. For all GRBs we place lower bounds on the distance to the progenitor, under the optimistic assumption of a gravitational-wave emission energy of 10^-2 M c^2 at 150 Hz, with a median limit of 17 Mpc. For short hard GRBs we place exclusion distances on binary neutron star and neutron star-black hole progenitors, using astrophysically motivated priors on the source parameters, with median values of 16 Mpc and 28 Mpc respectively. These distance limits, while significantly larger than for a search that is not aided by GRB satellite observations, are not large enough to expect a coincidence with a GRB. However, projecting these exclusions to the sensitivities of Advanced LIGO and Virgo, which should begin operation in 2015, we find that the detection of gravitational waves associated with GRBs will become quite possible.
A new class of X-ray binaries has been recently discovered by the high energy observatory, INTEGRAL. It is composed of intrinsically obscured supergiant high mass X-ray binaries, unveiled by means of multi-wavelength X-ray, optical, near- and mid-infrared observations, in particular photometric and spectroscopic observations using ESO facilities. However the fundamental questions about these intriguing sources, namely their formation, evolution, and the nature of their environment, are still unsolved. Among them, IGR J16318-4848 - a compact object orbiting around a supergiant B[e] star - seems to be one of the most extraordinary celestial sources of our Galaxy. We present here new ESO/VLT VISIR mid-infrared (MIR) spectroscopic observations of this source. First, line diagnostics allow us to confirm the presence of absorbing material (dust and cold gas) enshrouding the whole binary system, and to characterise the nature of this material. Second, by fitting broadband near to mid-infrared Spectral Energy Distribution - including ESO NTT/SofI, VLT/VISIR and Spitzer data - with a phenomenological model for sgB[e] stars, we show that the star is surrounded by an irradiated rim heated to a temperature of 3800-5500 K, along with a viscous disk component at an inner temperature of 750 K. VISIR data allow us to exclude the spherical geometry for the dust component. This detailed study will allow us in the future to get better constraints on the formation and evolution of such rare and short-living high mass X-ray binary systems in our Galaxy.
The sun as an oscillator produces frequencies which propagate in the heliosphere, via solar wind, to the terrestrial magnetosphere. We searched for those frequencies in the parameters of the near Earth solar plasma and the geomagnetic indices for the past four solar cycles. The solar wind parameters used in this work are the interplanetary magnetic field, plasma beta, Alfven Mach number, solar wind speed, plasma temperature, plasma pressure, plasma density and the geomagnetic indices DST, AE, Ap and Kp. We found out that each parameter of the solar wind exhibit certain periodicities which di?erentiate in each cycle. Our results indicate intermittent periodicities in our data, some of them shared between the solar wind parameters and geomagnetic indices.
The distribution of QSO radio luminosities has long been debated in the
literature. Some argue that it is a bimodal distribution, implying that there
are two separate QSO populations (normally referred to as 'radio-loud' and
'radio-quiet'), while others claim it forms a more continuous distribution
characteristic of a single population. We use deep observations at 20 GHz to
investigate whether the distribution is bimodal at high radio frequencies.
Carrying out this study at high radio frequencies has an advantage over
previous studies as the radio emission comes predominantly from the core of the
AGN, hence probes the most recent activity. Studies carried out at lower
frequencies are dominated by the large scale lobes where the emission is built
up over longer timescales (10^7-10^8 yrs), thereby confusing the sample. Our
sample comprises 874 X-ray selected QSOs that were observed as part of the 6dF
Galaxy Survey. Of these, 40% were detected down to a 3 sigma detection limit of
0.2-0.5 mJy.
No evidence of bimodality is seen in either the 20 GHz luminosity
distribution or in the distribution of the R_20 parameter: the ratio of the
radio to optical luminosities traditionally used to classify objects as being
either radio-loud or radio-quiet. Previous results have claimed that at low
radio luminosities, star formation processes can dominate the radio emission
observed in QSOs. We attempt to investigate these claims by stacking the
undetected sources at 20 GHz and discuss the limitations in carrying out this
analysis. However, if the radio emission was solely due to star formation
processes, we calculate that this corresponds to star formation rates ranging
from ~10 solar masses/yr to ~2300 solar masses/yr.
A new computational scheme for the nonlinear cosmological matter power spectrum (PS) is presented. It allows an analytic summation, at all orders in perturbation theory, of the leading contributions at small scales, thus extending to the PS the program initiated by Crocce and Scoccimarro for the nonlinear propagator. Our method is based on evolution equations in time, which can be cast in a form extremely convenient for fast numerical evaluations. A nonlinear PS is obtained in a time comparable to that needed for a simple 1-loop computation, and the numerical implementation is very simple. Our results agree with N-body simulations at the percent level in the BAO range of scales, and at the few-percent level up to $k ~ 1$ h/Mpc at $z >= 0.5$, thereby opening the possibility of applying this tool to scales interesting for weak lensing. We clarify the relation between our approach and previous ones, such as the Time Renormalization Group, and the multi-point propagator expansion. We discuss possible lines of improvements of the method and its intrinsic limitations by multi streaming at small scales and low redshifts.
After a long period of quiescence in \gamma-rays, blazar 0836+710 (4C +71.07) flared in the Spring of 2011. We found only limited multiwavelength coverage of the source. An indication of correlated optical / \gamma-ray variability is not surprising for a Flat Spectrum Radio Quasar (FSRQ) like this one. Radio observations at high frequencies, however, had seen a flare in 2010, well offset from possible \gamma-ray activity. The 2011 \gamma-ray activity comes during a period of rising radio emission, a pattern that has been seen since the EGRET era.
The high star formation rates of luminous infrared galaxies (LIRGs) make them ideal places for core-collapse supernova (CCSN) searches. At radio frequencies, free from dust extinction, it is possible to detect compact components within the innermost LIRG nuclear regions, such as SNe and SN remnants, as well as AGN buried deep in the LIRG nuclei. We studied the LIRG IC883 aiming at: (i) investigating its (circum-)nuclear regions using the e-EVN at 5GHz, and e-MERLIN at 6.9GHz, complemented by archival VLBI data; (ii) detecting at radio frequencies the two recently reported circumnuclear SNe 2010cu and 2011hi, which were discovered by near-IR (NIR) adaptive optics observations of IC883; and (iii) further investigating the nature of SN2011hi at NIR by means of observations with Gemini-North. The circumnuclear regions traced by e-MERLIN at 6.9GHz have an extension of ~1kpc, and show a striking double-sided structure, which very likely corresponds to a warped rotating ring, in agreement with previous studies. Our e-EVN observations at 5GHz and complementary archival VLBI data at 5GHz and 8.4GHz, reveal the presence of various milliarcsec compact components in the nucleus of IC883. A single compact source, an AGN candidate, dominates the emission at both nuclear and circumnuclear scales, as imaged with the e-EVN and e-MERLIN, respectively. The other milliarcsec components are very suggestive of ongoing nuclear CCSN activity. Our e-EVN observations also resulted in upper limits to the radio luminosity of the two SNe in IC883 recently discovered at NIR. We refine the classification of SN2011hi as a Type IIP SN according to our latest Gemini-North epoch from 2012, in agreement with a low-luminosity radio SN nature. We estimate a CCSN rate lower limit of 1.1_{-0.6}^{+1.3} yr^{-1} for the entire galaxy, based on three nuclear radio SNe and the circumnuclear SNe 2010cu and 2011hi. (abridged)
Polidan (1976) suggested that Be stars showing the CaII IR triplet in emission are interacting binaries. With the advent of the Gaia satellite, which will host a spectrometer to observe stars in the range 8470--8750 \AA, we carried out a spectroscopic survey of 150 Be stars, including Be binaries. We show that the Ca II triplet in emission, often connected with emission in Paschen lines, is an indicator of a peculiar environment in a Be star disc rather than a signature of an interacting binary Be star. However, Ca II emission without visible emission in Paschen lines is observed in interacting binary stars, as well as in peculiar objects. During the survey, a new interacting Be binary - HD 81357 - was discovered.
We have mapped in the 2.7 mm continuum and 12CO with the PdBI the IR-dark "tail" that crosses the IC 1396N globule from south to north, and is the most extincted part of this cloud. These observations have allowed us to distinguish all possible associations of molecular hydrogen emission features by revealing the presence of two well-collimated low-mass protostellar outflows at the northern part of the globule. The outflows are located almost in the plane of the sky and are colliding with each other towards the position of a strong 2.12 microns H2 line emission feature.
Large grids of synthetic spectra covering a widespread range of stellar parameters are mandatory for different stellar and (extra-)Galactic physics applications. Such large grids can be used for the automatic parametrisation of stellar spectra such as that performed within the AMBRE project for which the main goal is the stellar atmospheric parameters determination for the few hundreds of thousands of archived spectra of four ESO spectrographs. To fulfil the needs of AMBRE and future similar projects, we have computed a grid of synthetic spectra over the whole optical domain for cool to very cool stars of any luminosity with metallicities varying from 10-5 to 10 times the solar metallicity, and considering large variations in the chemical content of the {\alpha}-elements. New generation MARCS model atmospheres and the Turbospectrum code for radiative transfer have been used. We have also taken into account as complete as possible atomic and molecular linelists. A new grid of 16783 high resolution spectra over the wavelength range 3000 to 12000 {\AA} has been computed with a spectral resolution always larger than 150000. Normalised and absolute flux versions are available over a wide range of stellar atmospheric parameters for stars of FGKM spectral types. The covered parameters are 2500K\leqTeff\leq8000K, -0.5\leqlog(g)\leq5.5dex, -5.0\leq[M/H]\leq+1.0 dex and five different values of the enrichment in {\alpha}-elements have been considered (0.0, \pm0.2 dex and \pm0.4 dex around the standard values). This grid is made publicly available through the POLLUX database (about 50% of the spectra are already included in this database) and in FITS format upon request to the authors.
We determine the fraction of F, G, and K dwarfs in the Solar Neighborhood hosting hot jupiters as measured by the California Planet Survey from the Lick and Keck planet searches. We find the rate to be 1.2\pm0.38%, which is consistent with the rate reported by Mayor et al. (2011) from the HARPS and CORALIE radial velocity surveys. These numbers are more than double the rate reported by Howard et al. (2011) for Kepler stars and the rate of Gould et al. (2006) from the OGLE-III transit search, however due to small number statistics these differences are of only marginal statistical significance. We explore some of the difficulties in estimating this rate from the existing radial velocity data sets and comparing radial velocity rates to rates from other techniques.
We use new Suzaku observations of PKS 0745-191 to measure the thermodynamic properties of its ICM out to and beyond r_{200} (reaching 1.25r_{200}) with better accuracy than previously achieved, owing to a more accurate and better understood background model. We investigate and resolve the tensions between the previous Suzaku and ROSAT results for PKS 0745-191, which are found to be principally caused by incorrect background modelling in the previous Suzaku analysis. We investigate in depth the systematic errors affecting this observation, and present temperature, density, entropy and gas mass fraction profiles reaching out to and beyond the virial radius. We find that the entropy profile flattens in the outskirts as originally observed in the previous Suzaku analysis, but that the flattening starts at larger radius. The flattening of the entropy profile and our mass analysis suggests that outside ~17' (~1.9 Mpc) the ICM is out of hydrostatic equilibrium or the presence of significant non-thermal pressure support.
Several mechanisms have been proposed for the formation of brown dwarfs, but there is as yet no consensus as to which -- if any -- are operative in nature. Any theory of brown dwarf formation must explain the observed statistics of brown dwarfs. These statistics are limited by selection effects, but they are becoming increasingly discriminating. In particular, it appears (a) that brown dwarfs that are secondaries to Sun-like stars tend to be on wide orbits, $a\ga 100\,{\rm AU}$ (the Brown Dwarf Desert), and (b) that these brown dwarfs have a significantly higher chance of being in a close ($a\la 10\,{\rm AU}$) binary system with another brown dwarf than do brown dwarfs in the field. This then raises the issue of whether these brown dwarfs have formed {\it in situ}, i.e. by fragmentation of a circumstellar disc; or have formed elsewhere and subsequently been captured. We present numerical simulations of the purely gravitational interaction between a close brown-dwarf binary and a Sun-like star. These simulations demonstrate that such interactions have a negligible chance ($<0.001$) of leading to the close brown-dwarf binary being captured by the Sun-like star. Making the interactions dissipative by invoking the hydrodynamic effects of attendant discs might alter this conclusion. However, in order to explain the above statistics, this dissipation would have to favour the capture of brown-dwarf binaries over single brown-dwarfs, and we present arguments why this is unlikely. The simplest inference is that most brown-dwarf binaries -- and therefore possibly also most single brown dwarfs -- form by fragmentation of circumstellar discs around Sun-like protostars, with some of them subsequently being ejected into the field.
The time-symmetric block time--step (TSBTS) algorithm is a newly developed efficient scheme for $N$--body integrations. It is constructed on an era-based iteration. In this work, we re-designed the TSBTS integration scheme with dynamically changing era size. A number of numerical tests were performed to show the importance of choosing the size of the era, especially for long time integrations. Our second aim was to show that the TSBTS scheme is as suitable as previously known schemes for developing parallel $N$--body codes. In this work, we relied on a parallel scheme using the copy algorithm for the time-symmetric scheme. We implemented a hybrid of data and task parallelization for force calculation to handle load balancing problems that can appear in practice. Using the Plummer model initial conditions for different numbers of particles, we obtained the expected efficiency and speedup for a small number of particles. Although parallelization of the direct $N$--body codes is negatively affected by the communication/calculation ratios, we obtained good load balance results. Moreover, we were able to conserve the advantages of the algorithm (e.g., energy conservation for long--term simulations).
We present a study of the kinematical properties of a small sample of nearby near-infrared bright massive and intermediate mass young stellar objects using emission lines sensitive to discs and winds. We show for the first time that the broad ($\sim500$kms$^{-1}$) symmetric line wings on the HI Brackett series lines are due to Stark broadening or electron scattering, rather than pure Doppler broadening due to high speed motion. The results are consistent with the presence of a very dense circumstellar environment. In addition, many of these lines show evidence for weak line self-absorption, suggestive of a wind or disc-wind origin for that part of the absorbing material. The weakness of the self-absorption suggests a large opening angle for such an outflow. We also study the fluorescent 1.688$\mu$m FeII line, which is sensitive to dense material. We fitted a Keplerian disc model to this line, and find reasonable fits in all bar one case, in agreement with previous finding for classical Be stars that fluorescent iron transitions are reasonable disc tracers. Overall the picture is one in which these stars still have accretion discs, with a very dense inner circumstellar environment which may be tracing either the inner regions of a disc, or of a stellar wind, and in which ionised outflow is also present. The similarity with lower mass stars is striking, suggesting that at least in this mass range they form in a similar fashion.
I review what tidal tails in particular, collisional debris in general, might tell us about galaxies (their structure, current content and past mass assembly) about mergers in the nearby and distant Universe (major vs minor, wet vs dry, number evolution) and finally about the laws of gravity.
The reported alignment between the projected spin-axes and proper motion directions of pulsars is revisited in the light of new data from Jodrell Bank and Effelsberg. The present investigation uses 54 pulsars, the largest to date sample of pulsars with proper-motion and absolute polarisation, to study this effect. Our study has found strong evidence for pulsar spin-velocity alignment, excluding that those two vectors are completely uncorrelated, with >99% confidence. Although we cannot exclude the possibility of orthogonal spin-velocity configurations, comparison of the data with simulations shows that the scenario of aligned vectors is more likely than that of the orthogonal case. Moreover, we have determined the spread of velocities that a spin-aligned and spin-orthogonal distribution of kicks must have to produce the observed distribution of spin-velocity angle offsets. If the observed distribution of spin-velocity offset angles is the result of spin-aligned kicks, then we find that the distribution of kick-velocity directions must be broad with {\sigma}_v~30\degree if the orthogonal-kick scenario is assumed, then the velocity distribution is much narrower with {\sigma}_v<10\degree. Finally, in contrast to previous studies, we have performed robustness tests on our data, in order to determine whether our conclusions are the result of a statistical and/or systematic bias. The conclusion of a correlation between the spin and velocity vectors is independent of a bias introduced by subsets in the total sample. Moreover, we estimate that the observed alignment is robust to within 10% systematic uncertainties on the determination of the spin-axis direction from polarisation data.
Evidence is beginning to be put forward that demonstrates the role of the chromosphere in supplying energy and mass to the corona. We aim to asses the role of chromospheric jets in active region dynamics}{Using a combination of the {Hinode/SOT} Ca II H and TRACE 1550 {\AA} and 1600 {\AA} filters we examine chromospheric jets situated at the edge of a sunspot.}{Analysis reveals a near continuous series of jets, that raise chromospheric material into the low corona above a sunspot. The jets have average rise speeds of 30 km\,s^{-1} and a range of 10-100km\,s^{-1}. Enhanced emission observed at the jets leading edge suggests the formation of a shock front. Increased emission in TRACE bandpasses above the sunspot and the disappearance of the jets from the Ca II filter suggests that some of the chromospheric jet material is at least heated to \sim0.1MK. The evidence suggests that the jets could be a mechanism which provides a steady, low-level heating for active region features.
In this thesis we study several aspects of dynamical evolution of stellar clusters. The results of more than 200 simulations of single-mass star clusters with different initial total mass, half-mass radius and galactocentric distance, are reported. Recent studies of star clusters show a linear relation between a star cluster's dissolution time and its two-body relaxation time in logarithmic scale. We found that the single-mass star clusters do not show such a linear relation. We present new modified initial parameters to obtain a linear relation for single-mass star clusters. Also the evolution of multi-mass clusters and their lifetime, in the presence of the Galaxy is investigated. We simulate about 90 multi-mass star clusters with the Nbody6 code. These clusters have different initial total mass, half-mass radius and galactocentric distance. Finally we investigate the evolution of the stellar mass function and show that the slopes of the mass functions decrease with time. In addition we study the effect of galactocentric distance of star clusters on the evolution of the mass function.
We present the results of a search for planetary companions orbiting near hot Jupiter planet candidates (Jupiter-size candidates with orbital periods near 3 days) identified in the Kepler data through its sixth quarter of science operations. Special emphasis is given to companions between the 2:1 interior and exterior mean-motion resonances. A photometric transit search excludes companions with sizes ranging from roughly 2/3 to 5 times the size of the Earth, depending upon the noise properties of the target star. A search for dynamically induced deviations from a constant period (transit timing variations or TTVs) also shows no significant signals. In contrast, comparison studies of warm Jupiters (with slightly larger orbits) and hot Neptune-size candidates do exhibit signatures of additional companions with these same tests. These differences between hot Jupiters and other planetary systems denote a distinctly different formation or dynamical history.
A fraction of the extragalactic near-infrared (near-IR) background light involves redshifted photons from the ultraviolet (UV) emission from galaxies present during reionization at redshifts above 6. The absolute intensity and the anisotropies of the near-IR background provide an observational probe of the first-light galaxies and their spatial distribution. We estimate the extragalactic background light intensity during reionization by accounting for the stellar and nebular emission from first-light galaxies. We require the UV photon density from these galaxies to generate a reionization history that is consistent with the optical depth to electron scattering from cosmic microwave background measurements. We also require the bright-end luminosity function of galaxies in our models to reproduce the measured Lyman drop-out luminosity functions at redshifts of 6 to 8. The absolute intensity is about 0.1 to 0.3 nW m$^{-2}$ sr$^{-1}$ at the peak of its spectrum at $\sim$ 1.1 $\mu$m. We also discuss the anisotropy power spectrum of the near-IR background using a halo model to describe the galaxy distribution. We compare our predictions for the anisotropy power spectrum to existing measurements from deep near-IR imaging data from {\it Spitzer}/IRAC, {\it Hubble}/NICMOS, and {\it AKARI}. The predicted rms fluctuations at tens of arcminute angular scales are roughly an order of magnitude smaller than the existing measurements. While strong arguments have been made that the measured fluctuations do not have an origin involving faint low-redshift galaxies, we find that the existing measurements are also incompatible with an origin during the era of reionization. The measured near-IR background anisotropies remain unexplained and could be associated with an unidentified non-astrophysical origin.
We present the elemental abundance and H2 content measurements of a Damped Lyman-{\alpha} (DLA) system with an extremely large H i column density, log N(H i) (cm-2) = 22.0+/-0.10, at zabs = 3.287 towards the QSO SDSS J 081634+144612. We measure column densities of H2, C i, C i^*, Zn ii, Fe ii, Cr ii, Ni ii and Si ii from a high signal-to-noise and high spectral resolution VLT-UVES spectrum. The overall metallicity of the system is [Zn/H] = -1.10 +/- 0.10 relative to solar. Two molecular hydrogen absorption components are seen at z = 3.28667 and 3.28742 (a velocity separation of \approx 52 km s-1) in rotational levels up to J = 3. We derive a total H2 column density of log N(H2) (cm-2) = 18.66 and a mean molecular fraction of f = 2N(H2)/[2N(H2) + N(H i)] = 10-3.04+/-0.37, typical of known H2-bearing DLA systems. From the observed abundance ratios we conclude that dust is present in the Interstellar Medium (ISM) of this galaxy, with a enhanced abundance in the H2-bearing clouds. However, the total amount of dust along the line of sight is not large and does not produce any significant reddening of the background QSO. The physical conditions in the H2-bearing clouds are constrained directly from the column densities of H2 in different rotational levels, C i and C i^* . The kinetic temperature is found to be T = 75 K and the particle density lies in the range nH = 50-80 cm-3 . The neutral hydrogen column density of this DLA is similar to the mean H i column density of DLAs observed at the redshift of {\gamma}-ray bursts (GRBs). We explore the relationship between GRB-DLAs and high column density end of QSO-DLAs finding that the properties (metallicity and depletion) of DLAs with log N(H i) > 21.5 in the two populations do not appear to be significantly different.
{Abridged} Rapid variations in optical flux are seen in many quasars and all
blazars. The amount of variability in different classes of Active Galactic
Nuclei has been studied extensively but many questions remain unanswered. We
present the results of a long-term programme to investigate the intra-night
optical variability (INOV) of powerful flat spectrum radio core-dominated
quasars (CDQs), with a focus on probing the relationship of INOV to the degree
of optical polarization. We observed a sample of 16 bright CDQs showing strong
broad optical emission lines and consisting of both high and low optical
polarization quasars (HPCDQs and LPCDQs). We employed ARIES, IIA, IGO
telescopes, to carry out {\it R}-band monitoring on a total of 47 nights.
Combining these INOV data with those taken from the literature, we were able to
increase the sample size to 21 CDQs(12 LPCDQs and 9 HPCDQs) monitored on a
total of 73 nights. As the existence of a prominent flat-spectrum radio core
signifies that strong relativistic beaming is present in all these CDQs, the
definitions of the two sets differ primarily in fractional optical
polarization, the LPCDQs showing a very low median$ P_{op} \simeq$ 0.4 per
cent.
Our study yields an INOV duty cycle (DC) of $\sim$28 per cent for the LPCDQs
and $\sim 68$ percent for HPCDQs.
If only strong INOV with fractional amplitude above 3 per cent is considered,
the corresponding DCs are $\sim$ 7 per cent and $\sim$ 40 per cent,
respectively.From this strong contrast between the two classes of luminous,
relativistically beamed quasars, it is apparent that relativistic beaming is
normally not a sufficient condition for strong INOV and a high optical
polarization is the other necessary condition.
The motion of the Earth around the Sun causes an annual change in the magnitude and direction of the arrival velocity of dark matter particles on Earth, in a way analogous to aberration of stellar light. In directional detectors, aberration of weakly interacting massive particles (WIMPs) modulates the pattern of nuclear recoil directions in a way that depends on the orbital velocity of the Earth and the local galactic distribution of WIMP velocities. Knowing the former, WIMP aberration can give information on the latter, besides being a curious way of confirming the revolution of the Earth and the extraterrestrial provenance of WIMPs. While observing the full aberration pattern requires extremely large exposures, we claim that the annual variation of the mean recoil direction or of the event counts over specific solid angles may be detectable with moderately large exposures. For example, integrated counts over galactic hemispheres separated by planes perpendicular to Earth's orbit would modulate annually, resulting in Galactic Hemisphere Annual Modulations (GHAM) with amplitudes larger than the usual non-directional annual modulation.
Type II SNe can be used as a star formation tracer to probe the metallicity distribution of global low-redshift star formation. We present oxygen and iron abundance distributions of type II supernova progenitor regions that avoid many previous sources of bias, and can serve as a standard of comparison for properly observationally evaluating how different classes of supernovae depend on progenitor metallicity. In contrast to previous supernova host metallicity studies, this sample is homogeneous and is drawn from an areal rather than a targeted survey, so supernovae in the lowest-mass galaxies are not excluded. We spectroscopically measure the gas-phase oxygen abundance near a representative subsample of the hosts of type II supernovae from the first-year Palomar Transient Factory (PTF) supernova search. The median metallicity is 12+log(O/H) = 8.65 and the median host galaxy stellar mass from fits to SDSS photometry is 10^9.9 solar masses. Though iron abundance is more central to the evolution of massive stars than oxygen abundance, it cannot be measured directly in extragalactic HII regions. Using the relationship between iron and oxygen abundances found for Milky Way disk, bulge, and halo stars, we can translate our distribution of type II SN environments as a function of oxygen abundance into an estimate of the iron abundance, and find the median [Fe/H] = -0.60.
[abridged] We present results of modeling the SED and multiwavelength variability of the bright FSRQ PKS1510-089 with our time-dependent multizone Monte Carlo/Fokker-Planck code (Chen et al. 2001). As primary source of seed photons for inverse Compton scattering, we consider radiation from the broad line region (BLR), from the molecular torus, and the local synchrotron radiation (SSC). Different scenarios are assessed by comparing simulated light curves and SEDs with one of the best flares by PKS1510-089, in March 2009. The time-dependence of our code and its correct handling of light travel time effects allow us to fully take into account the effect of the finite size of the active region, and in turn to fully exploit the information carried by time resolved observed SEDs, increasingly available since the launch of Fermi. We confirm that the spectrum adopted for the external radiation has an important impact on the modeling of the SED, in particular for the lower energy end of the Compton component, observed in the X-ray band, which in turn is one of the most critical bands to assess the differences between EC and SSC emission. In the context of the scenario presented here, where the flaring is caused by the increase of the number of relativistic electrons ascribed to the effect of the interaction of a portion of the jet (blob) with a shock, we can not firmly discriminate the three main scenarios for gamma-ray emission. However, results show clearly the differences produced by a more realistic treatment of the emitting source in the shape of SEDs and their time variability over relevant, observable time-scales, and demonstrate the crucial importance of time-dependent multi-zone models to advance our understanding of the physics of these sources, by taking full advantage of the wealth of information offered by the high quality data of current multiwavelength campaigns.
The temporal variation of the horizontal velocity in subsurface layers beneath three different types of active regions is studied using the technique of ring diagrams. In this study, we select active regions (ARs) 10923, 10930, 10935 from three consecutive Carrington rotations: AR 10930 contains a fast-rotating sunspot in a strong emerging active region while other two have non-rotating sunspots with emerging flux in AR 10923 and decaying flux in AR 10935. The depth range covered is from the surface to about 12 Mm. In order to minimize the influence of systematic effects, the selection of active and quiet regions is made so that these were observed at the same heliographic locations on the solar disk. We find a significant variation in both components of the horizontal velocity in active regions as compared to quiet regions. The magnitude is higher in emerging-flux regions than in the decaying-flux region, in agreement with earlier findings. Further, we clearly see a significant temporal variation in depth profiles of both zonal and meridional flow components in AR 10930, with the variation in the zonal component being more pronounced. We also notice a significant influence of the plasma motion in areas closest to the rotating sunspot in AR 10930 while areas surrounding the non-rotating sunspots in all three cases are least affected by the presence of the active region in their neighborhood.
We discuss the subtle relationship between so-called massive gravity (that is, gravity incorporating a non-zero graviton mass) and bimetric gravity, focussing particularly on the manner in which massive gravity may be viewed as a suitable limit of bimetric gravity. The limiting procedure is more delicate than currently appreciated, and in particular, in a cosmological context can lead to an interesting interplay between the "background" and "foreground" metrics. The fact that in bimetric theories one always has two sets of metric equations of motion, one for each metric, continues to have an effect even in the massive gravity limit. Thus, solutions of bimetric gravity in the limit of vanishing kinetic term are also solutions of massive gravity, but the contrary statement is not necessarily true.
Results are presented from radioactivity screening of two models of photomultiplier tubes designed for use in current and future liquid xenon experiments. The Hamamatsu 5.6 cm diameter R8778 PMT, used in the LUX dark matter experiment, has yielded a positive detection of four common radioactive isotopes: 238U, 232Th, 40K, and 60Co. Screening of LUX materials has rendered backgrounds from other detector materials subdominant to the R8778 contribution. A prototype Hamamatsu 7.6 cm diameter R11410 MOD PMT has also been screened, with benchmark isotope counts measured at <0.4 238 U / <0.3 232 Th / <8.3 40 K / 2.0+-0.2 60 Co mBq/PMT. This represents a large reduction, equal to a change of \times 1/24 238U / \times 1/9 232Th / \times 1/8 40K per PMT, between R8778 and R11410 MOD, concurrent with a doubling of the photocathode surface area (4.5 cm to 6.4 cm diameter). 60Co measurements are comparable between the PMTs, but can be significantly reduced in future R11410 MOD units through further material selection. Assuming PMT activity equal to the measured 90% upper limits, Monte Carlo estimates indicate that replacement of R8778 PMTs with R11410 MOD PMTs will change LUX PMT electron recoil background contributions by a factor of \times1/25 after further material selection for 60Co reduction, and nuclear recoil backgrounds by a factor of \times 1/36. The strong reduction in backgrounds below the measured R8778 levels makes the R11410 MOD a very competitive technology for use in large-scale liquid xenon detectors.
Recent particle-in-cell (PIC) simulations of the Kelvin-Helmholtz instability have revealed the emergence of a strong and large-scale DC magnetic field component at the shear interface, which is not captured by the standard linear two-fluid theory. We show that the DC magnetic field results from electron mixing across the shear interface. The mixing mechanism can be modeled by a an electron thermal expansion across the shear, in a warm shear scenario, and we connect this picture to the cold shear scenario where the development of the standard cold fluid KHI produces an effective average temperature that drives the expansion. We outline a simple analytical model that describes the growth and saturation level of the DC magnetic field.
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