The ambipolar-diffusion theory of star formation predicts the formation of fragments in molecular clouds with mass-to-flux ratios greater than that of the parent-cloud envelope. By contrast, scenarios of turbulence-induced fragmentation do not yield such a robust prediction. Based on this property, Crutcher et al. (2009) proposed an observational test that could potentially discriminate between fragmentation theories. However, the analysis applied to the data severely restricts the discriminative power of the test: the authors conclude that they can only constrain what they refer to as the "idealized" ambipolar-diffusion theory that assumes initially straight-parallel magnetic field lines in the parent cloud. We present an original, self-consistent analysis of the same data taking into account the nonuniformity of the magnetic field in the cloud envelopes, which is suggested by the data themselves, and we discuss important geometrical effects that must be accounted for in using this test. We show quantitatively that the quality of current data does not allow for a strong conclusion about any fragmentation theory. Given the discriminative potential of the test, we urge for more and better-quality data.
We study the evolution of galaxies inside and outside of the group environment since z=1 using a large well defined set of groups and galaxies from the zCOSMOS-bright redshift survey in the COSMOS field. The fraction of galaxies with early-type morphologies increases monotonically with M_B luminosity and stellar mass and with cosmic epoch. It is higher in the groups than elsewhere, especially at later epochs. The emerging environmental effect is superposed on a strong global mass-driven evolution, and at z~0.5 and log(M*/Msol)~10.2, the "effect" of group environment is equivalent to (only) about 0.2 dex in stellar mass or 2 Gyr in time. The stellar mass function of galaxies in groups is enriched in massive galaxies. We directly determine the transformation rates from late to early morphologies, and for transformations involving colour and star formation indicators. The transformation rates are systematically about twice as high in the groups as outside, or up to 3-4 times higher correcting for infall and the appearance of new groups. The rates reach values, for masses around the crossing mass 10^10.5 Msol, as high as (0.3-0.7)/Gyr in the groups, implying transformation timescales of 1.4-3 Gyr, compared with less than 0.2/Gyr, i.e. timescales >5 Gyr, outside of groups. All three transformation rates decrease at higher stellar masses, and must decrease also at the lower masses below 10^10 Msol which we cannot well probe. The rates involving colour and star formation are consistently higher than those for morphology, by a factor of about 50%. Our conclusion is that the transformations which drive the evolution of the overall galaxy population since z~1 must occur at a rate 2-4 times higher in groups than outside of them.
We present Spitzer IRAC photometry of white dwarf remnants of 14 stars with M = 3-5 Msol. We do not detect mid-infrared excess around any of our targets. By demanding a 3 sigma photometric excess at 4.5 micron for unresolved companions, we rule out planetary mass companions down to 5, 7, or 10 M_J for 13 of our targets based on the Burrows et al. (2003) substellar cooling models. Combined with previous IRAC observations of white dwarf remnants of intermediate-mass stars, we rule out \geq 10 M_J companions around 40 white dwarfs and \geq 5 M_J companions around 26 white dwarfs.
Massive galaxies at high-z have smaller effective radii than those today, but similar central densities. Their size growth therefore relates primarily to the evolving abundance of low-density material. Various models have been proposed to explain this evolution, which have different implications for galaxy, star, and BH formation. We compile observations of spheroid properties as a function of redshift and use them to test proposed models. Evolution in progenitor gas-richness with redshift gives rise to initial formation of smaller spheroids at high-z. These systems can then evolve in apparent or physical size via several channels: (1) equal-density 'dry' mergers, (2) later major or minor 'dry' mergers with less-dense galaxies, (3) adiabatic expansion, (4) evolution in stellar populations & mass-to-light-ratio gradients, (5) age-dependent bias in stellar mass estimators, (6) observational fitting/selection effects. If any one of these is tuned to explain observed size evolution, they make distinct predictions for evolution in other galaxy properties. Only model (2) is consistent with observations as a dominant effect. It is the only model which allows for an increase in M_BH/M_bulge with redshift. Still, the amount of merging needed is larger than that observed or predicted. We therefore compare cosmologically motivated simulations, in which all these effects occur, & show they are consistent with all the observational constraints. Effect (2), which builds up an extended low-density envelope, does dominate the evolution, but effects 1,3,4, & 6 each contribute ~20% to the size evolution (a net factor ~2). This naturally also predicts evolution in M_BH-sigma similar to that observed.
We analyze multi-field inflationary systems which yield strongly scale dependent non-Gaussianity with a shape that is very close to the local shape. As in usual multi-field models, the non-Gaussianity arises from the non-linear transfer of scalar field fluctuations to curvature perturbations. Here we consider models in which higher order terms (loops) dominate over the lowest order source of non-linearity. The magnitude of non-Gaussianity depends on an infrared cutoff which is determined by our observational probes measuring non-Gaussianity. In our models, the running is positive and large (n_{NG} ~ 0.2) on CMB scales. The magnitude of the bispectrum is maximally of order O(100), and grows on small scales. This can lead to interesting signals for large scale structure.
Realistic accretion disk models require a number of ingredients, including viscous fluids, electromagnetic fields and general relativistic corrections. Close to the innermost stable circular orbit (ISCO) the latter can be appreciable and (quasi-)Newtonian approximations become unreliable. This is particularly true for nearly extremal black holes like GRS 1915+105, where the ISCO almost coincides with the black hole horizon. To describe the physics close to the ISCO adequately in a simplified model we approximate the nearly extremal Kerr geometry by the near-horizon extremal Kerr geometry and construct in this background relativistic viscous fluid solutions with electromagnetic fields. We discuss some applications of our solutions and possible relations to the Kerr/CFT correspondence.
There are now many known exoplanets with Msin(i) within a factor of two of Neptune's, including the transiting planets GJ436b and HAT-P-11b. Planets in this mass-range are different from their more massive cousins in several ways that are relevant to their radiative properties and thermal structures. By analogy with Neptune and Uranus, they are likely to have metal abundances that are an order of magnitude or more greater than those of larger, more massive planets. This increases their opacity, decreases Rayleigh scattering, and changes their equation of state. Furthermore, their smaller radii mean that fluxes from these planets are roughly an order of magnitude lower than those of otherwise identical gas giant planets. Here, we compute a range of plausible radiative equilibrium models of GJ436b and HAT-P-11b. In addition, we explore the dependence of generic Neptune-mass planets on a range of physical properties, including their distance from their host stars, their metallicity, the spectral type of their stars, the redistribution of heat in their atmospheres, and the possible presence of additional optical opacity in their upper atmospheres.
The formation of brown dwarfs (BDs) due to the fragmentation of proto-stellar
disks undergoing pairwise encounters was investigated. High resolution allowed
the use of realistic initial disk models where both the vertical structure and
the local Jeans mass were resolved. The results show that objects with masses
ranging from giant planets to low mass stars can form during such encounters
from initially stable disks. The parameter space of initial spin-orbit
orientations and the azimuthal angles for each disk was explored. An upper
limit on the initial Toomre Q value of ~2 was found for fragmentation to occur.
Depending on the initial configuration, shocks, tidal-tail structures and mass
inflows were responsible for the condensation of disk gas. Retrograde disks
were generally more likely to fragment. When the interaction timescale was
significantly shorter than the disks' dynamical timescales, the proto-stellar
disks tended to be truncated without forming objects.
The newly-formed objects had masses ranging from 0.9 to 127 Jupiter masses,
with the majority in the BD regime. They often resided in star-BD multiples and
in some cases also formed hierarchical orbiting systems. Most of them had large
angular momenta and highly flattened, disk-like shapes. The objects had radii
ranging from 0.1 to 10 AU. The disk gas was assumed to be locally isothermal,
appropriate for the short cooling times in extended proto-stellar disks, but
not for condensed objects. An additional case with explicit cooling that
reduced to zero for optically thick gas was simulated to test the extremes of
cooling effectiveness and it was still possible to form objects in this case.
Detailed radiative transfer is expected to lengthen the internal evolution
timescale for these objects, but not to alter our basic results.
We study the effects of modified theories of gravity on the cosmic microwave background (CMB) anisotropies power spectrum, and in particular on its large scales, where the integrated Sachs-Wolfe (ISW) effect is important. Starting with a general parametrisation, we then specialise to f(R) theories and theories with Yukawa-type interactions between dark matter particles. In these models, the evolution of the metric potentials is altered, and the contribution to the ISW effect can differ significantly from that in the standard model of cosmology. We proceed to compare these predictions with observational data for the CMB and the ISW, performing a full Monte Carlo Markov chain (MCMC) analysis. In the case of f(R) theories, the result is an upper limit on the lengthscale associated to the extra scalar degree of freedom characterising these theories. With the addition of data from the Hubble diagram of Type Ia supernovae, we obtain an upper limit on the lengthscale of the theory of B_0 < 0.4, or equivalently \lambda_1 < 1900 Mpc/h at 95% c.l. improving previous CMB constraints. For Yukawa-type models we get a bound on the coupling 0.75 < \beta_1 < 1.25 at the 95% c.l. We also discuss the implications of the assumed priors on the estimation of modified gravity parameters, showing that a marginally less conservative choice improves the f(R) constraints to \lambda_1 < 1400 Mpc/h, or B_0 < 0.2 at 95% c.l.
Observations of hundreds of supersoft x-ray sources (SSSs) in external galaxies have shed light on the diversity of the class and on the natures of the sources. SSSs are linked to the physics of Type Ia supernovae and accretion-induced collapse, ultraluminous x-ray sources and black holes, the ionization of the interstellar medium, and tidal disruption by supermassive black holes. The class of SSSs has an extension to higher luminosities: ultraluminous SSSs have luminosities above 10^39 erg/s. There is also an extension to higher energies: quasisoft x-ray sources (QSSs) emit photons with energies above 1 eV, but few or none with energies above 2 keV. Finally, a significant fraction of the SSSs found in external galaxies switch states between observations, becoming either quasisoft or hard. For many systems ``supersoft'' refers to a temporary state; SSSs are sources, possibly including a variety of fundamentally different system types, that pass through such a state. We review those results derived from extragalactic data and related theoretical work that are most surprising and that suggest directions for future research.
Optical spectroscopy using the echellete spectrograph and imager (ESI) on Keck II are presented for nearby major mergers of gas-rich galaxies. These Ultraluminous Infrared Galaxy (ULIRG) spectra show strong A star features and H alpha emission, indicating recent starburst activity. We find that the strength of the H beta absorption line increases with the projected distance from the center of the merger. We interpret this H beta equivalent width (W$_{H\beta}$) as a measure of the time since star formation rapidly decreased, indicating older populations in the outer regions of the merger remnant. The time since star formation diminished in the outer regions increases with radius, while the star formation history in the central kpc is consistent with continuous star formation. We interpret this result as evidence that gas depletion occurs first in the outer disk, likely due to merger-induced gas inflow. Our empirical constraint on the gas inflow timescale is central to modeling merger-induced star formation and AGN activity. Theoretical models accurately predict the total amount of infalling gas but guess the timescale.
We present the results of extensive multi-frequency monitoring of the radio galaxy 3C 120 between 2002 and 2007 at X-ray, optical, and radio wave bands, as well as imaging with the Very Long Baseline Array (VLBA). Over the 5 yr of observation, significant dips in the X-ray light curve are followed by ejections of bright superluminal knots in the VLBA images. Consistent with this, the X-ray flux and 37 GHz flux are anti-correlated with X-ray leading the radio variations. This implies that, in this radio galaxy, the radiative state of accretion disk plus corona system, where the X-rays are produced, has a direct effect on the events in the jet, where the radio emission originates. The X-ray power spectral density of 3C 120 shows a break, with steeper slope at shorter timescale and the break timescale is commensurate with the mass of the central black hole based on observations of Seyfert galaxies and black hole X-ray binaries. These findings provide support for the paradigm that black hole X-ray binaries and active galactic nuclei are fundamentally similar systems, with characteristic time and size scales linearly proportional to the mass of the central black hole. The X-ray and optical variations are strongly correlated in 3C 120, which implies that the optical emission in this object arises from the same general region as the X-rays, i.e., in the accretion disk-corona system. We numerically model multi-wavelength light curves of 3C 120 from such a system with the optical-UV emission produced in the disk and the X-rays generated by scattering of thermal photons by hot electrons in the corona. From the comparison of the temporal properties of the model light curves to that of the observed variability, we constrain the physical size of the corona and the distances of the emitting regions from the central BH.
How does the tidal debris of minor galaxy mergers contribute to structures in spiral galaxies or in the intergalactic medium? While major mergers are known to create structures such as tidal dwarf galaxies and star clusters within their tidal debris, less is known about minor mergers (mass ratios between a dwarf galaxy and disk galaxy of less than one-third) and their tidal debris. This work surveys 6 nearby minor mergers using optical broad-band and H-alpha narrow-band imaging to characterize star formation in their tidal debris. Young star clusters with ages less than the dynamical age of the tidal tails are found in all 6 mergers, indicating that the star clusters formed in situ. Even if minor mergers contribute less tidal debris per interaction than major mergers, they are more common and possibly contribute structure to all types of galaxies and to the intergalactic medium throughout the history of the universe.
Gas at intermediate temperature between the hot X-ray emitting coronal gas in galaxies at the centers of galaxy clusters, and the much cooler optical line emitting filaments, yields information on transport processes and plausible scenarios for the relationship between X-ray cool cores and other galactic phenomena such as mergers or the onset of an active galactic nucleus. Hitherto, detection of intermediate temperature gas has proven elusive. Here, we present FUV imaging of the "low excitation" emission filaments of M87 and show strong evidence for the presence of CIV 1549 A emission which arises in gas at temperature ~10^5K co-located with Halpha+[NII] emission from cooler ~10^4K gas. We infer that the hot and cool phases are in thermal communication, and show that quantitatively the emission strength is consistent with thermal conduction, which in turn may account for many of the observed characteristics of cool core galaxy clusters.
We present evidence for interaction between the supernova remnant (SNR)
G357.7+0.3 and nearby molecular clouds, leading to the formation of wind-swept
structures and bright emission rims. These features are not observed at visual
wavelengths, but are clearly visible in mid-infrared (MIR) mapping undertaken
using the Spitzer Space Telescope (SST). Analysis of one of these clouds, the
bright cometary structure G357.46+0.60, suggests that it contains strong
polycyclic aromatic hydrocarbon (PAH) emission features in the 5.8 and 8.0
microns photometric bands, and that these are highly variable over relatively
small spatial scales. This source also appears to contain a YSO within the
bright rim structure, with a steeply rising spectrum between 1.25 and 24
microns.
Finally, it is noted that a further, conical emission region appears to be
associated with the Mira V1139 Sco, and it is suggested that this may represent
the case of a Mira outflow interacting with a SNR.
We present mid-infrared (MIR) photometry for 367 Galactic disk, bulge and Large Magellanic Cloud (LMC) planetary nebulae, determined using GLIMPSE II and SAGE data acquired using the Spitzer Space Telescope. This has permitted us to make a comparison between the luminosity functions of bulge and LMC planetary nebulae, and between the MIR colours of all three categories of source. It is determined that whilst the 3.6 microns luminosity function of the LMC and bulge sources are likely to be closely similar, the [3.6]-[5.8] and [5.8]-[8-0] indices of LMC nebulae are different from those of their disk and bulge counterparts. This may arise because of enhanced 6.2 microns PAH emission within the LMC sources, and/or as a result of differences between the spectra of LMC PNe and those of their Galactic counterparts. We also determine that the more evolved disk sources listed in the MASH catalogues of Parker et al. and Miszalski et al. (2008) have similar colours to those of the less evolved (and higher surface brightness) sources in the catalogue of Acker et al. (1992); a result which appears at variance with previous studies of these sources.
Fukui et al. (2006) discovered two molecular loops in the Galactic center and argued that the foot points of the molecular loops, two bright spots at the both loop ends, represent the gas accumulated by the falling motion along the loops, subsequent to the magnetic flotation by the Parker instability. We have carried out sensitive CO observations of the foot points toward l = 356 deg. at a few pc resolution in the six rotational transitions of CO; 12CO(J=1-0, 3-2, 4-3, 7-6), 13CO(J=1-0) and C18O(J=1-0). The high resolution image of 12CO(J=3-2) has revealed detailed distribution of the high excitation gas including a U shape, the outer boundary of which shows sharp intensity jumps accompanying strong velocity gradients. An analysis of the multi-J CO transitions shows that temperature is in a range from 30 - 100 K or higher and density is around 10^3 - 10^4 /cm^3, confirming that the foot points have high temperature and density although there is no radiative heat source like high mass stars in and around the loops. We argue that the high temperature is likely due to the shock heating under C-shock condition caused by the magnetic flotation. We made a detailed comparison of the distribution obtained with theoretical numerical simulations and note that the U shape seems to be consistent with numerical simulations. We also find that the region of highest temperature of 60 K or higher inside the U shape corresponds to the spur having upward flow, additionally heated up either by magnetic reconnection or bouncing in the interaction with the narrow "neck" at the bottom of the U shape. We note these new findings further reinforce the magnetic floatation interpretation.
We investigate the problem of probing the local spatial structure of the magnetic field of the interstellar medium using multi-frequency polarized maps of the synchrotron emission at radio wavelengths. We focus in this paper on the three-dimensional reconstruction of the largest scales of the magnetic field, relying on the internal depolarization (due to differential Faraday rotation) of the emitting medium as a function of electromagnetic frequency. We argue that multi-band spectroscopy in the radio wavelengths, developed in the context of high-redshift extragalactic HI lines, can be a very useful probe of the 3D magnetic field structure of our Galaxy when combined with a Maximum A Posteriori reconstruction technique. When starting from a fair approximation of the magnetic field, we are able to recover the true one by using a linearized version of the corresponding inverse problem. The spectral analysis of this problem allows us to specify the best sampling strategy in electromagnetic frequency and predicts a spatially anisotropic distribution of posterior errors. The reconstruction method is illustrated for reference fields extracted from realistic magneto-hydrodynamical simulations.
MICADO is the adaptive optics imaging camera being studied for the E-ELT. Its design has been optimised for use with MCAO, but will have its own SCAO module for the initial operational phase; and in principle could also be used with GLAO or LTAO. In this contribution, we outline a few of the science drivers for MICADO and show how these have shaped its design. The science drivers have led to a number of requirements on the AO system related to astrometry, photometry, and PSF uniformity. We discuss why these requirements have arisen and what might be done about them.
We are presenting new results on kinematics and structure of the Mrk 334 Seyfert galaxy. Panoramic (3D) spectroscopy is performed at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences using the MPFS integral-field spectrograph and scanning Fabry--Perot interferometer. The deep images have revealed that Mrk 334 is observed during the final stage of its merging with a massive companion. A possible mass ratio ranges from 1/5 to 1/3. The merger has triggered mass redistribution in the disk resulting in an intensification of nuclear activity and in a burst of star formation in the inner region of the galaxy. The circumnuclear starburst is so intense that its contribution to the gas ionization exceeds that contribution of the AGN. We interpret the nuclear gas outflow with velocities of ~200 km/s as a galactic superwind that accompanies the violent star formation. This suggestion is consistent with the asymmetric X-ray brightness distribution in Mrk 334. The trajectory of the fragments of the disrupted satellite in the vicinity of the main galaxy nucleus can be traced. In the galaxy disk a cavern is found that is filled with a low-density ionized gas. We consider this region to be the place where the remnants of the companion have recently penetrated through the gaseous disk of the main galaxy.
Aims. The accretion of stars onto the central supermassive black hole at the
center of the Milky Way is predicted to generate large fluxes of
subrelativistic ions in the Galactic center region. We analyze the intensity,
shape and spatial distribution of de-excitation gamma-ray lines produced by
nuclear interactions of these energetic particles with the ambient medium.
Methods. We first estimate the amount and mean kinetic energy of particles
released from the central black hole during star disruption. We then calculate
from a kinetic equation the energy and spatial distributions of these particles
in the Galactic center region. These particle distributions are then used to
derive the characteristics of the main nuclear interaction gamma-ray lines.
Results. Because the time period of star capture by the supermassive black
hole is expected to be shorter than the lifetime of the ejected fast particles
against Coulomb losses, the gamma-ray emission is predicted to be stationary.
We find that the nuclear de-excitation lines should be emitted from a region of
maximum 5$^\circ$ angular radius. The total gamma-ray line flux below 8 MeV is
calculated to be $\approx10^{-4}$ photons cm$^{-2}$ s$^{-1}$. The most
promising lines for detection are those at 4.44 and $\sim$6.2 MeV, with a
predicted flux in each line of $\approx$$10^{-5}$ photons cm$^{-2}$ s$^{-1}$.
Unfortunately, it is unlikely that this emission can be detected with the
INTEGRAL observatory. But the predicted line intensities appear to be within
reach of future gamma-ray space instruments. A future detection of
de-excitation gamma-ray lines from the Galactic center region would provide
unique information on the high-energy processes induced by the central
supermassive black hole and the physical conditions of the emitting region.
We report a possible detection of an ~4.6-hour quasi-periodic oscillation (QPO) in the 0.3-10 keV emission of the high-energy peaked blazar PKS 2155-304 from a 64 ks observation by the XMM-Newton EPIC/pn detector. We identify a total modulation of ~5% in the light curve and confirm that nominal period by periodogram, structure function and wavelet analyses. The limited light curve duration allows the capture of only 3.8 cycles of this oscillation and thus precludes a very strong claim for this QPO, despite a nominally high (>3 sigma) statistical significance. We briefly discuss models capable of producing an X-ray QPO of such a period in a blazar.
Recently a second type of spicules was discovered at the solar limb with the Solar Optical Telescope (SOT) onboard the Japanese Hinode spacecraft. These previously unrecognized type II spicules are thin chromospheric jets that are shorter-lived (10-60 s) and that show much higher apparent upward velocities (of order 50-100 km/s) than the classical spicules. Since they have been implicated in providing hot plasma to coronal loops, their formation, evolution and properties are important ingredients for a better understanding of the mass and energy balance of the low solar atmosphere. Here we report on the discovery of the disk counterparts of type II spicules using spectral imaging data in the Ca II 854.2 nm and Halpha lines with the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish Solar Telescope (SST) in La Palma. We find rapid blueward excursions in the line profiles of both chromospheric lines that correspond to thin, jet-like features that show apparent velocities of order 50 km/s. These blueward excursions seem to form a separate absorbing component with Doppler shifts of order 20 and 50 km/s for the Ca II 854.2 nm and Halpha line respectively. We show that the appearance, lifetimes, longitudinal and transverse velocities and occurrence rate of these rapid blue excursions on the disk are very similar to those of the type II spicules at the limb. A detailed study of the spectral line profiles in these events suggests that plasma is accelerated along the jet, and plasma is being heated throughout the short lifetime of the event.
My aim in this talk is to make clear that there are two sides to galaxy formation: the properties of the galaxies themselves, and the properties of the material that is left over from the galaxy formation process. To date, galaxy formation studies have focused on correctly predicting the properties of galaxies, and I will review the tremendous level of success in this area. However, these models usually ignore the ``flip side'' of galaxy formation: the intergalactic medium and the intra-group/intra-cluster medium (ICM). Yet, Chandra and XMM have given us a good view of the ICM and their results present an equally important challenge for theoretical models. I will show that this challenge is far from easy to meet, but describe the Bower et al 2008 model of galaxy formation which successfully combines both sides of the observational constraints.
The physical and evolutionary relation between growing supermassive black holes (AGN) and host galaxies is currently the subject of intense research activity. Nevertheless, a deep theoretical understanding of such a relation is hampered by the unique multi-scale nature of the combined AGN-galaxy system, which defies any purely numerical, or semi-analytic approach. Various physical process active on different scales have signatures in different parts of the electromagnetic spectrum; thus, observations at different wavelengths and theoretical ideas all should contribute towards a "large dynamic range" view of the AGN phenomenon. As an example, I will focus in this review on two major recent observational results on the cosmic evolution of supermassive black holes, focusing on the novel contribution given to the field by the COSMOS survey. First of all, I will discuss the evidence for the so-called "downsizing" in the AGN population as derived from large X-ray surveys. I will then present new constraints on the evolution of the black hole-galaxy scaling relation at 1<z<2 derived by exploiting the full multi-wavelength coverage of the survey on a complete sample of ~90 type 1 AGN.
It is conjectured that energy sources of the gamma ray bursts are similar to
energy sources which trigger solar and stellar transient activity phenomena
like flares, plasma accelerated flows in the flux tubes and, dissipation of
energy and acceleration of particles by the MHD waves. Phenomenologically we
examine in detail the following energy sources which may trigger gamma ray
bursts : (i) cosmic primordial flares which could be solar flare like phenomena
in the region of inter galactic or inter galactic cluster regions, (ii)
primordial magnetic flux tubes that might have been formed from the convective
collapse of the primordial magnetic flux (iii) nonlinear interaction and
dissipation of MHD waves that are produced from the perturbations of
large-scale inter galactic or inter cluster magnetic field of primordial
origin. We examine in detail each of the afore mentioned phenomena keeping in
mind that whether such processes are responsible for energy sources of the
gamma ray bursts.
By considering the similarity of observations and prevailing physical
conditions in the cosmic environment, the following study suggests that most
likely and a promising energy source for creation of the gamma ray bursts may
be due to primordial flares.
By considering similar observed properties of gamma ray bursts (GRB) and solar flares with the prevailing physical conditions in the cosmic environment, the following study suggests that most likely and promising energy source for the central engine which triggers GRB may be due to primordial flares, solar flare like phenomena, at the sites of inter galactic or inter galactic clusters in the early universe. The derived energy-redshift relation, E = E_{0}{(1+z)}^3 (where E is the amount of energy released, z is the redshift of GRB and E_{0} is a constant which is estimated to be ~ 10^{52} ergs), from the simple flare mechanism, is confirmed from the least square fit with the observed energy-redshift relation. Some of the physical parameters like length scale, strength of magnetic field, etc., of the flaring region of the GRB are estimated.
The origin of large-scale magnetic field in the universe is one of the greatest mysteries in modern cosmology. We present a new mechanism for generation of large-scale magnetic field, based on the power-counting renormalizable theory of gravitation recently proposed by Horava. Contrary to the usual case in general relativity, the U(1) gauge symmetry of a Maxwell action in this theory permits terms breaking conformal invariance in the ultraviolet. Moreover, for high frequency modes, the anisotropic scaling intrinsic to the theory inevitably makes the sound horizon far outside the Hubble horizon. Consequently, non-inflationary cosmic expansion in the early universe naturally generates super-horizon quantum fluctuations of the magnetic field. Specializing our consideration to the case with the dynamical critical exponent $z=3$, we show an explicit set of parameters for which (i) the amplitude of generated magnetic field is large enough as a seed for the dynamo mechanism; (ii) backreaction to the cosmic expansion is small enough; and (iii) the high-energy dispersion relation is consistent with the most recent observational limits from MAGIC and FERMI.
We introduce a new physical recipe into the De Lucia and Blaizot version of the Munich semi-analytic model built upon the Millennium dark matter simulation: the tidal stripping of stellar material from satellite galaxies during mergers. To test the significance of the new physical process we apply a Monte Carlo Markov Chain parameter estimation technique constraining the model with the $K$-band luminosity function, $B-V$ colours and the black hole-bulge mass relation. The differences in parameter correlations, and in the allowed regions in likelihood space, reveal the impact of the new physics on the basic ingredients of the model, such as the star-formation laws, feedback recipes and the black hole growth model. With satellite disruption in place, we get a model likelihood four times higher than in the original model, indicating that the new process seems to be favoured by observations. This is achieved mainly due to a reduction in black hole growth that produces a better agreement between the properties of central black holes and host galaxies. Compared to the best-fit model without disruption, the new model removes the excess of dwarf galaxies in the original recipe with a more modest supernova heating. The new model is now consistent with the three observational data sets used to constrain it, while significantly improving the agreement with observations for the distribution of metals in stars. Moreover, the model now follows the build up of intra-cluster light.
General criteria to check the positivity of the distribution function (phase-space consistency) of stellar systems of assigned density and anisotropy profile are useful starting points in Jeans-based modeling. Here we substantially extend previous results, and we present the inversion formula and the analytical necessary and sufficient conditions for phase-space consistency of the family of multi-component Cuddeford spherical systems: the distribution function of each density component of these systems is defined as the sum of an arbitrary number of Cuddeford distribution functions with arbitrary values of the anisotropy radius, but identical angular momentum exponent. The radial trend of anisotropy that can be realized by these models is therefore very general. As a surprising by-product of our study, we found that the ``central cusp-anisotropy theorem'' (a necessary condition for consistency relating the values of the central density slope and of the anisotropy parameter) holds not only at the center, but at all radii in consistent multi-component generalized Cuddeford systems. This last result suggests that the so--called mass--anisotropy degeneracy could be less severe than what is sometimes feared.
The power spectrum is obtained for the Kolmogorov stochasticity parameter map for WMAP's cosmic microwave background (CMB) radiation temperature datasets. The interest for CMB Kolmogorov map is that it can carry direct information about voids in the matter distribution, so that the correlations in the distribution of voids have to be reflected in the power spectrum. Although limited by the angular resolution of the WMAP, this analysis shows the possibility of acquiring this crucial information via CMB maps. Even the already obtained behavior, some of which is absent in the simulated maps, can influence the development of views on the void correlations at the large-scale web formation.
Meng, Chen & Han (2009) comprehensively and systemically studied the WD + MS system by detailed binary evolution calculations. Following their studies, we have carried out a series of binary population synthesis studies about the properties of the companions of SNe Ia for different metallicities $Z$. We present the distributions of the masses, $M_{\rm 2}^{\rm SN}$, the radii, $R_{\rm 2}^{\rm SN}$, of companions, and the periods, $P_{\rm SN}$, and the ratios of separations to radii, $A/R_{\rm 2}^{\rm SN}$, of WD + MS systems for various $Z$ at the moment of supernova explosion. These arameters can be applied to constrain the numerical simulation of the interaction between the ejecta of a supernova and its companion. We also show the distributions of some integral properties of companions, i.e. the mass, the space velocity and the surface gravity, for various $Z$ after the interaction. The distributions may help to search companion in a supernova remnant. All the parameters above significantly change with $Z$. Incorporating the simulation results of interaction between supernovae ejecta and companions in Marietta et al. (2000) and Kasen et al. (2004) into our binary population synthesis study, we found that more than 75% of all supernovae have enough polarization signal which can be detected by spectropolarimetric observations. We also found that 13 to 14 per cent SNe Ia belong to the supernovae like 1991T, which is consistent with observations within errors. This may indicate that SNe 1991T-like have not any special properties in physics except for the viewing angle of an observer.
We have been able to connect the statistics of the observed double image gravitational lenses to the general properties of the internal structure of dark matter haloes. Our analytical theory for the GNFW lenses with parametrized cusp slope (alpha) gives us a relation connecting the cusp slope of the lensing profile to the observed magnification ratio of the produced images and location of the optical axis. The relation does not depend on cosmology, total lens mass, concentration or redshifts of the the lens and the lensed object. Simple geometry of axially symmetric lensing and aforementioned relation enables us to define a threshold value alpha_CSL for the cusp slope, independent from location of the optical axis. The threshold cusp slope value alpha=alpha_CSL is the shallowest slope for the inner part of the GNFW profile that can produce the observed magnification ratio with any lensing configuration. We use distribution of these threshold values in a statistical study of the double image lenses in order to limit the possible cusp slope values, and identify whether there exists a population of haloes with similar profiles. Our theoretical fit indicates that within our sample of double image gravitational lenses, most of the haloes have cusp slope alpha=-1.95 +/- 0.02. We have also found an indication of a second population of lenses with a cusp slope value alpha=-1.49 +/- 0.09. We estimate that there is about 99 per cent probability that the observed feature in the threshold value limit distribution is produced by the second population of lenses, with their own characteristic density profile.
We investigate the statistical equilibrium of Co in the atmospheres of cool stars, and the influence of NLTE and HFS (hyperfine splitting) on the formation of Co lines and abundances. Significant departures from LTE level populations are found for Co I, also number densities of excited states in Co II differ from LTE at low metallicity. The NLTE abundance of Co in solar photosphere is 4.95 +/- 0.04 dex, which is in agreement with that in C I meteorites within the combined uncertainties. The spectral lines of Co I were calculated using the results of recent measurements of hyperfine interaction constants by UV Fourier transform spectrometry. For Co II, the first laboratory measurements of hyperfine structure splitting A and B factors were performed. A differential abundance analysis of Co is carried out for 18 stars in the metallicity range -3.12 < [Fe/H] < 0. The abundances are derived by method of spectrum synthesis. At low [Fe/H], NLTE abundance corrections for Co I lines are as large as +0.6 >... +0.8 dex. Thus, LTE abundances of Co in metal-poor stars are severely underestimated. The stellar NLTE abundances determined from the single UV line of Co II are lower by ~0.5-0.6 dex. The discrepancy might be attributed to possible blends that have not been accounted for in the solar Co II line and its erroneous oscillator strength. The increasing [Co/Fe] trend in metal-poor stars, as calculated from the Co I lines under NLTE, can be explained if Co is overproduced relative to Fe in massive stars. The models of galactic chemical evolution are wholly inadequate to describe this trend suggesting that the problem is in SN yields.
Aims. The detailed analysis of all data taken by the XMM-Newton satellite of
UGC11763 to characterize the different components that are emitting and
absorbing radiation in the vicinity of the active nucleus.
Methods. The continuum emission was studied through the EPIC spectra taking
profit of the spectral range of these cameras. The high resolution RGS spectra
were analyzed in order to characterize the absorbing features and the emission
line features that arise in the spectra of this source.
Results. A power law with a photon index \Gamma = 1.72^{+0.03}_{-0.01}
accounts for the continuum emission of this source in the hard X-rays from 10
down to 1 keV. At lower energies, a black body model with kT= 0.100\pm 0.003
keV provides a good description of the observed soft excess. The absorption
signatures in the spectra of UGC11763 are consistent with the presence of a two
phase ionized material (log U=1.65^{+0.07}_{-0.08}; 2.6\pm 0.1 and log N_{H} =
21.2\pm 0.2; 21.51\pm 0.01 cm^{-2}, respectively) in the line of sight. The
physical conditions found are consistent with the two phases being in pressure
equilibrium. The low ionization component is more ionized than typically found
for warm absorbers in other Seyfert 1 galaxies. There are also signatures of
some emission lines: Ovii He$\alpha$(r), Ovii He$\alpha$(f), a blend of the
Neix He$\alpha$ triplet and Fexviii at \lambda 17.5 \AA.
In this study we address the question under which conditions a saturated velocity field stemming from geodynamo simulations leads to an exponential growth of the magnetic field in a corresponding kinematic calculation. We perform global self-consistent geodynamo simulations and calculate the evolution of a kinematically advanced tracer field. The self-consistent velocity field enters the induction equation in each time step, but the tracer field does not contribute to the Lorentz force. This experiment has been performed by Cattaneo & Tobias (2009) and is closely related to the test field method by Schrinner et al. (2005, 2007). We find two dynamo regimes in which the tracer field either grows exponentially or approaches a state aligned with the actual self-consistent magnetic field after an initial transition period. Both regimes can be distinguished by the Rossby number and coincide with the dipolar and multipolar dynamo regimes identified by Christensen & Aubert (2006). Dipolar dynamos with low Rossby number are kinematically stable whereas the tracer field grows exponentially in the multipolar dynamo regime. This difference in the saturation process for dynamos in both regimes comes along with differences in their time variability. Within our sample of 20 models, solely kinematically unstable dynamos show dipole reversals and large excursions. The complicated time behaviour of these dynamos presumably relates to the alternating growth of several competing dynamo modes. On the other hand, dynamos in the low Rossby number regime exhibit a rather simple time dependence and their saturation merely results in a fluctuation of the fundamental dynamo mode about its critical state.
We present the largest spectroscopic follow-up performed in SWIRE ELAIS-N1. We were able to determine redshifts for 289 extragalactic sources. The values of spectroscopic redshifts of the latter have been compared with the estimated values from our photometric redshift code with very good agreement between the two for both galaxies and quasars. Six of the quasars are hyperluminous infrared galaxies all of which are broad line AGN. We have performed emission line diagnostics for 30 sources using the $[OIII]$ / $H$$\beta$, $[NII]$ / $H$$\alpha$, $[SII]$ / $H$$\alpha$ and $[OI]$ / $H$$\alpha$ line ratios in order to classify these 30 sources into star-forming, Seyferts or LINER. It is revealed that narrow line AGN do not lie in the IRAC color-color space proposed by Lacy et al (2004) for AGN but occupy a distinct parameter space in the same IRAC color-color diagram. Infrared SED fitting suggests that these are all starburst dominated or quiescent galaxies. Any dust torus present must be very weak.
Aims. We investigate the long-term evolution of the large-scale photospheric
magnetic field geometry of the solar-type star HD 190771. With fundamental
parameters very close to the Sun's except a shorter rotation period of 8.8 d,
HD 190771 provides us with a first insight into the specific impact of the
rotation rate in the dynamo generation of magnetic fields in 1 Msun stars.
Methods. We use circularly polarized, high-resolution spectra obtained with
the NARVAL spectropolarimeter (Observatoire du Pic du Midi, France) and compute
cross-correlation line profiles with high signal-to-noise ratio in order to
detect polarized Zeeman signatures. From three phase-resolved data sets
collected during the summers of 2007, 2008 and 2009, we model the large-scale
photospheric magnetic field of the star by means of Zeeman-Doppler imaging and
follow its temporal evolution.
Results. The comparison of the magnetic maps reveals a polarity reversal of
the axisymmetric component of the large-scale magnetic field between 2007 and
2008, this evolution being observed both in the poloidal and toroidal magnetic
components. Between 2008 and 2009, another type of global evolution occurs,
with a sharply decreased fraction of magnetic energy stored in the toroidal
component. These changes are not accompanied by a significant evolution of the
total photospheric magnetic energy. Using our spectra to perform radial
velocity measurements, we also report the detection of a very low-mass stellar
companion to HD 190771.
We investigate the linear correlation coefficient between the intensities at different wavelengths in photospheric and chromospheric spectral lines. Waves that propagate vertically through the stratified solar atmosphere affect different wavelengths at different times. This leads to a characteristic pattern of (non-)coherence of the intensity at various wavelengths. We derived the correlation matrices for several photospheric and chromospheric spectral lines from observations. For comparison with the observations, we calculate correlation matrices for spectra from LTE modeling approaches, 1-D NLTE simulations, and a 3-D MHD simulation run. We apply the correlation method also to temperature maps at different optical depth layers. We find that all photospheric spectral lines show a similar pattern: a pronounced asymmetry of the correlation between line core and red or blue wing. The pattern cannot be reproduced with a simulation of the granulation pattern, but with waves that travel upwards. All chromospheric spectral lines show a more complex pattern. In the case of Ca II H, the 1-D NLTE simulations of monochromatic waves produce a correlation matrix that qualitatively matches to the observations. The photospheric signature is well reproduced in the matrix derived from the 3-D MHD simulation. The correlation matrices of observed photospheric and chromospheric spectral lines are highly structured with characteristic and different patterns in every spectral line. The comparison with matrices derived from simulations and simple modeling suggests that the main driver of the detected patterns are upwards propagating waves. Application of the correlation method to 3-D temperature cubes seems to be a promising tool for a detailed comparison of simulation results and observations in future studies.
We present a new "collisional grooming" algorithm that enables us to model images of debris disks where the collision time is less than the Poynting Robertson time for the dominant grain size. Our algorithm uses the output of a collisionless disk simulation to iteratively solve the mass flux equation for the density distribution of a collisional disk containing planets in 3 dimensions. The algorithm can be run on a single processor in ~1 hour. Our preliminary models of disks with resonant ring structures caused by terrestrial mass planets show that the collision rate for background particles in a ring structure is enhanced by a factor of a few compared to the rest of the disk, and that dust grains in or near resonance have even higher collision rates. We show how collisions can alter the morphology of a resonant ring structure by reducing the sharpness of a resonant ring's inner edge and by smearing out azimuthal structure. We implement a simple prescription for particle fragmentation and show how Poynting-Robertson drag and fragmentation sort particles by size, producing smaller dust grains at smaller circumstellar distances. This mechanism could cause a disk to look different at different wavelengths, and may explain the warm component of dust interior to Fomalhaut's outer dust ring seen in the resolved 24 micron Spitzer image of this system.
This tutorial paper describes the problem of image reconstruction from interferometric data with a particular focus on the specific problems encountered at optical (visible/IR) wavelengths. The challenging issues in image reconstruction from interferometric data are introduced in the general framework of inverse problem approach. This framework is then used to describe existing image reconstruction algorithms in radio interferometry and the new methods specifically developed for optical interferometry.
We address the formation of 3D nullpoint topologies in the solar corona by combining Hinode/XRT observations of a small dynamic limb event, which occurred beside a non-erupting prominence cavity, with a 3D zero-beta MHD simulation. To this end, we model the boundary-driven kinematic emergence of a compact, intense, and uniformly twisted flux tube into a potential field arcade that overlies a weakly twisted coronal flux rope. The expansion of the emerging flux in the corona gives rise to the formation of a nullpoint at the interface of the emerging and the pre-existing fields. We unveil a two-step reconnection process at the nullpoint that eventually yields the formation of a broad 3D fan-spine configuration above the emerging bipole. The first reconnection involves emerging fields and a set of large-scale arcade field lines. It results in the launch of a torsional MHD wave that propagates along the arcades, and in the formation of a sheared loop system on one side of the emerging flux. The second reconnection occurs between these newly formed loops and remote arcade fields, and yields the formation of a second loop system on the opposite side of the emerging flux. The two loop systems collectively display an anenome pattern that is located below the fan surface. The flux that surrounds the inner spine field line of the nullpoint retains a fraction of the emerged twist, while the remaining twist is evacuated along the reconnected arcades. The nature and timing of the features which occur in the simulation do qualititatively reproduce those observed by XRT in the particular event studied in this paper. Moreover, the two-step reconnection process suggests a new consistent and generic model for the formation of anemone regions in the solar corona.
The timescale for star formation, a measure of how quickly neutral gas is being converted to stars, is considerably longer than typical dynamical timescales associated with a galactic disk. For purposes of modeling galaxy evolution, however, it would be extremely attractive if the star formation timescale were proportional to an easily derived dynamical timescale. We compare estimates of the star formation timescale within nearby galaxies, based on the work of Leroy et al. (2008) and existing BIMA SONG CO data, with three simple forms of the dynamical time: the orbital time, the free-fall time at the midplane density, and the disk Jeans time (the growth time for gravitational instabilities in a disk). When taking into account the gravity of the stellar disk in an approximate way, all three timescales show correlations with the star formation timescale, though none of the correlations can be accurately described as linear. Systematic errors in estimating appropriate gas masses and the stellar velocity dispersion may obscure an underlying correlation, but we focus instead on a model where the timescale for H_2 formation from HI is decoupled from the timescale for star formation from H_2. The Jeans time correlates well with the first of these timescales, but the relationship is still non-linear, and requires a characteristic GMC lifetime that increases toward galaxy centers.
The abundance of dark matter satellites and subhalos, the existence of density cusps at the centers of dark matter halos, and problems producing realistic disk galaxies in simulations are issues that have raised concerns about the viability of the standard cold dark matter (LambdaCDM) scenario for galaxy formation. This article reviews these issues, and considers the implications for cold vs. various varieties of warm dark matter (WDM). The current evidence appears to be consistent with standard LambdaCDM, although improving data may point toward a rather tepid version of LambdaWDM -- tepid since the dark matter cannot be very warm without violating observational constraints.
In models of natural inflation, the inflaton is an axion-like particle. Unfortunately, axion potentials in UV-complete theories appear to be too steep to drive inflation. We show that, even for a steep potential, natural inflation can occur if the coupling between axion and gauge fields is taken into account. Due to this coupling, quanta of the gauge field are produced by the rolling of the axion. If the coupling is large enough, such a dissipative effect slows down the axion, leading to inflation even for a steep potential. The spectrum of perturbations is quasi-scale invariant, but in the simplest construction its amplitude is larger than $10^{-5}$. We discuss a possible way out of this problem.
Inflation generically produces primordial gravitational waves with a red spectral tilt. In this paper we calculate the backreaction produced by these gravitational waves on the expansion of the universe. We find that in radiation domination the backreaction acts as a relativistic fluid, while in matter domination a small dark energy emerges with an equation of state w=-8/9.
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Dark energy dynamics in the recent universe is influenced by its evolution through the long, matter dominated expansion history. A particular dynamical property, the flow variable, remains constant in several classes of scalar field models as long as matter dominates; the dark energy is only free to diverge in behavior at recent times. This gives natural initial conditions for Monte Carlo studies of dark energy dynamics. We propose a parametrization for the later evolution that covers a wide range of possible behaviors, is tractable in making predictions, and can be constrained by observations. We compare the approach to directly parametrizing the potential, which does not take into account the maturity of the dark energy dynamics.
Using deep Chandra observations of the Hydra A galaxy cluster, we examine the metallicity structure near the central galaxy and along its powerful radio source. We show that the metallicity of the intracluster medium is enhanced by up to 0.2 dex along the radio jets and lobes compared to the metallicity of the undisturbed gas. The enhancements extend from a radius of 20 kpc from the central galaxy to a distance of ~ 120 kpc. We estimate the total iron mass that has been transported out of the central galaxy to be between 2 x 10^7 M_sun and 7 x 10^7 M_sun which represents 10% - 20% of the iron mass within the central galaxy. The energy required to lift this gas is roughly 1% to 5% of the total energetic output of the AGN. Evidently, Hydra A's powerful radio source is able to redistribute metal-enriched, low entropy gas throughout the core of the galaxy cluster. The short re-enrichment time scale < 10^9 yr implies that the metals lost from the central galaxy will be quickly replenished.
Globular star clusters are among the first stellar populations to have formed in the Milky Way, and thus only a small sliver of their initial spectrum of stellar types are still burning hydrogen on the main-sequence today. Almost all of the stars born with more mass than 0.8 M_sun have evolved to form the white dwarf cooling sequence of these systems, and the distribution and properties of these remnants uniquely holds clues related to the nature of the now evolved progenitor stars. With ultra-deep HST imaging observations, rich white dwarf populations of four nearby Milky Way globular clusters have recently been uncovered, and are found to extend an impressive 5 - 8 magnitudes in the faint-blue region of the H-R diagram. In this paper, we characterize the properties of these population II remnants by presenting the first direct mass measurements of individual white dwarfs near the tip of the cooling sequence in the nearest of the Milky Way globulars, M4. Based on Gemini/GMOS and Keck/LRIS multiobject spectroscopic observations, our results indicate that 0.8 M_sun population II main-sequence stars evolving today form 0.53 +/- 0.01 M_sun white dwarfs. We discuss the implications of this result as it relates to our understanding of stellar structure and evolution of population II stars and for the age of the Galactic halo, as measured with white dwarf cooling theory.
We present the spectra of 24 white dwarfs in the direction of the globular cluster Messier 4 obtained with the Keck/LRIS and Gemini/GMOS spectrographs. Determining the spectral types of the stars in this sample, we find 24 type DA and 0 type DB (i.e., atmospheres dominated by hydrogen and helium respectively). Assuming the ratio of DA/DB observed in the field with effective temperature between 15,000 - 25,000 K, i.e., 4.2:1, holds for the cluster environment, the chance of finding no DBs in our sample due simply to statistical fluctuations is only 6 X 10^(-3). The spectral types of the ~100 white dwarfs previously identified in open clusters indicate that DB formation is strongly suppressed in that environment. Furthermore, all the ~10 white dwarfs previously identified in other globular clusters are exclusively type DA. In the context of these two facts, this finding suggests that DB formation is suppressed in the cluster environment in general. Though no satisfactory explanation for this phenomenon exists, we discuss several possibilities.
We have searched for star-forming galaxies at z~7 by applying the Lyman-break technique to newly-released 1.1micron Y-band images from WFC3 on HST. By comparing these images of the Hubble Ultra Deep Field with the ACS z'-band (0.85micron), we identify objects with red colours, (z'-Y)_AB>1.3), consistent with the Ly-alpha forest absorption at z~6.7-8.8. We identify 12 of these z'-drops down to a limiting magnitude Y_AB<28.5 (equivalent to a star formation rate of 1.3M_sun/yr at z=7.1), which are undetected in the other ACS filters. We use the WFC3 J-band image to eliminate contaminant low mass Galactic stars, which typically have redder colours than z~7 galaxies. One of our z'-drops is a probably a T-dwarf star. The z~7 z'-drops have much bluer spectral slopes than Lyman-break galaxies at lower redshift. Our brightest z'-drop is not present in the NICMOS J-band image of the same field taken 5 years before, and is a possible transient object. From the 10 remaining z~7 candidates we determine a lower limit on the star formation rate density of 0.0017M_sun/yr/Mpc^3 for a Salpeter initial mass function, which rises to 0.0025-0.0034M_sun/yr/Mpc^3 after correction for luminosity bias. The star formation rate density is a factor of ~10 less than that at z=3-4, and is about half the value at z~6. While based on a single deep field, our results suggest that this star formation rate density would produce insufficient Lyman continuum photons to reionize the Universe unless the escape fraction of these photons is extremely high (f_esc>0.5), and the clumping factor of the Universe is low. Even then, we need to invoke a large contribution from galaxies below our detection limit. The apparent shortfall in ionizing photons might be alleviated if stellar populations at high redshift are low metallicity or have a top-heavy IMF.
We present a novel method for calculating the primordial non-Gaussianity produced by super-horizon evolution during inflation. Our method evolves the distribution of coarse-grained inflationary field values using a transport equation. We present simple evolution equations for the moments of this distribution, such as the variance and skewness. This method possesses some conceptual advantages over existing techniques. Among them, it cleanly separates multiple sources of non-Gaussianity and may diagnose `tuned' inflaton trajectories. It has computational advantages when compared with popular alternatives, such as the `delta-N' framework. We adduce numerical calculations demonstrating that our new method offers good agreement with those already in the literature. We focus on two fields and the fNL parameter, but we expect that our method will generalize to multiple scalar fields and to moments of arbitrarily high order. We present our expressions in a field-space covariant form which we postulate to be valid for any number of fields.
X-ray properties of galaxy groups can unlock some of the most challenging research topics in modern extragalactic astronomy: the growth of structure and its influence on galaxy formation. Only with the advent of the Chandra and XMM facilities have X-ray observations reached the depths required to address these questions in a satisfactory manner. Here we present an X-ray imaging study of two patches from the CNOC2 spectroscopic galaxy survey using combined Chandra and XMM data. A state of the art extended source finding algorithm has been applied, and the resultant source catalog, including redshifts from a spectroscopic follow-up program, is presented. The total number of spectroscopically identified groups is 25 spanning a redshift range 0.04-0.79. Approximately 50% of CNOC2 spectroscopically selected groups in the deeper X-ray (RA14h) field are likely X-ray detections, compared to 20% in the shallower (RA21h) field. Statistical modeling shows that this is consistent with expectations, assuming an expected evolution of the Lx-M relation. A significant detection of a stacked shear signal for both spectroscopic and X-ray groups indicates that both samples contain real groups of about the expected mass. We conclude that the current area and depth of X-ray and spectroscopic facilities provide a unique window of opportunity at z~0.4 to test the X-ray appearance of galaxy groups selected in various ways. There is at present no evidence that the correlation between X-ray luminosity and velocity dispersion evolves significantly with redshift, which implies that catalogs based on either method can be fairly compared and modeled.
High-contrast imaging observations of large angular diameter stars enable complementary science questions to be addressed compared to the baseline goals of proposed missions like the Terrestrial Planet Finder-Coronagraph, New World's Observer, and others. Such targets however present a practical problem in that finite stellar size results in unwanted starlight reaching the detector, which degrades contrast. In this paper, we quantify the sensitivity, in terms of contrast, of an internally-occulting, space-based coronagraph as a function of stellar angular diameter, from unresolved dwarfs to the largest evolved stars. Our calculations show that an assortment of band-limited image masks can accommodate a diverse set of observations to help maximize mission scientific return. We discuss two applications based on the results: the spectro-photometric study of planets already discovered with the radial velocity technique to orbit evolved stars, which we elucidate with the example of Pollux b, and the direct detection of planets orbiting our closest neighbor, Alpha Centauri, whose primary component is on the main-sequence but subtends an appreciable angle on the sky. It is recommended that similar trade studies be performed with other promising internal, external, and hybrid occulter designs for comparison, as there is relevance to a host of interesting topics in planetary science and related fields.
We have carried out high-angular resolution (1.4") observations in the continuum at 3.1mm and in the N2H+ 1-0, CH3CN 5_k-4_k and 13CS 2-1 lines using the Plateau de Bure Interferometer (PdBI) towards the intermediate mass (IM) protostar IRAS21391+5802 (IC1396N). In addition, we have merged the PdBI images with previous BIMA (continuum data at 1.2mm and 3.1mm) and single-dish (N2H+ 1-0) data to have a comprehensive description of the region. The combination of our data with BIMA and 30m data show that the bipolar outflow associated has completely eroded the initial molecular globule. The 1.2mm and 3.1mm continuum emissions are extended along the outflow axis tracing the warm walls of the biconical cavity. Most of the molecular gas, however, is located in an elongated feature in the direction perpendicular to the outflow. A strong chemical differentiation is detected across the molecular toroid, with the N2H+ 1-0 emission absent in the inner region.This chemical differentiation can be understood in terms of the different gas kinetic temperature. The [CH3CN]/[N2H+] ratio increases by 5 orders of magnitude with gas temperature, for temperatures between 20K and 100K. The CH3CN abundance towards IRAM 2A, the most massive protostellar core, is similar to that found in hot corinos and lower than that expected towards IM and high mass hot cores. This could indicate that IRAM 2A is a low mass or at most Herbig Ae star (IRAM 2A) instead of the precursor of a massive Be star. Alternatively, the low CH3CN abundance could also be the consequence of IRAM 2A being a Class 0/I transition object which has already formed a small photodissociation region (PDR).
It is surprising to find dust around B type stars, as in the case of B[e] stars. These stars exhibit a dense, dusty environment witnessed by their infrared-excess and many emission lines from permitted and forbidden transitions. Given the large uncertainties on their distances, this spectral type gathers many different kind of sources that may harbor a similar circumstellar environment, i.e. a dense dusty disk. At the exception of Young Stellar Objects, in many cases, it is very difficult to understand the origin of such a disk without invoking binarity. We describe current powerful methods, like spectral disentangling, spectro-astrometry and long baseline interferometry, to detect especially close binaries amongst the unclassified B[e] stars. The role of binary mergers in the formation of the B[e] phenomenon, especially in supergiants and compact PNe, is also discussed.
We present the analysis of the Polycyclic Aromatic Hydrocarbon (PAH) spectra of a sample of 92 typical star forming galaxies at 0.03 < z < 0.2 observed with the Spitzer IRS. We compare the relative strengths of PAH emission features with SDSS optical diagnostics to probe the relationship between PAH grain properties and star formation and AGN activity. Short-to-long wavelength PAH ratios, and in particular the 7.7-to-11.3 micron feature ratio, are strongly correlated with the star formation diagnostics D_n(4000) and H-alpha equivalent width, increasing with younger stellar populations. This ratio also shows a significant difference between active and non-active galaxies, with the active galaxies exhibiting weaker 7.7 micron emission. A hard radiation field as measured by [OIII]/H-beta and [NeIII]_15.6/[NeII]_12.8 affects PAH ratios differently depending on whether this field results from starburst activity or an AGN. Our results are consistent with a picture in which larger PAH molecules grow more efficiently in richer media and in which smaller PAH molecules are preferentially destroyed by AGN.
A new numerical code, designed for the detailed numerical treatment of nonlinear diffusive shock acceleration, is used for modeling of particle acceleration and radiation in young supernova remnants. The model is based on spherically symmetric hydrodynamic equations complemented with transport equations for relativistic particles. For the first time, the acceleration of electrons and protons by both forward and reverse shocks is studied through detailed numerical calculations. We model the energy spectra and spatial distributions of nonthermal emission of the young supernova remnant RX J1713.7-3946 and compare the calculations with the spectral and morphological properties of this object obtained in broad energy band from radio to very high energy gamma-rays. We discuss the advantages and shortcomings of the so-called hadronic and leptonic models which assume that the observed TeV gamma-ray emission is produced by accelerated protons and electrons, respectively. We discuss also a "composite" scenario when the gamma-ray flux from the main parts of the shell has inverse Compton origin, but with a non-negligible contribution of hadronic origin from dense clouds interacting with the shell.
The Lidov-Kozai mechanism allows a body to periodically exchange its eccentricity with inclination. It was first discussed in the framework of the quadrupolar secular restricted three-body problem, where the massless particle is the inner body, and later extended to the quadrupolar secular nonrestricted three body problem. In this paper, we propose a different point of view on the problem by looking first at the restricted problem where the massless particle is the outer body. In this situation, equilibria at high mutual inclination appear, which correspond to the population of stable particles that Verrier & Evans (2008,2009) find in stable, high inclination circumbinary orbits around one of the components of the quadruple star HD 98800. We provide a simple analytical framework using a vectorial formalism for these situations. We also look at the evolution of these high inclination equilibria in the non restricted case.
Using a simple color selection based on B-, z- and K-band photometry, BzK=
(z-K)_AB-(B-z)_AB>-0.2, we picked out 52 star-forming galaxies at 1.4<z<2.5
(sBzKs) from a K-band selected sample (K_Vega<22.0) in an area of ~5.5 arcmin^2
of the Hubble Ultra Deep Field (UDF). We develop a new photometric redshift
method, and the error in our photometric redshifts is less than 0.02(1+z). From
the photometric redshift distribution, we find the BzK color criterion can be
used to select star-forming galaxies at 1.4<z<2.5 with K_Vega<22.0.
Down to K_Vega<22.0, the number counts of sBzKs increase linearly with the
K-band magnitude; the sBzKs are strongly clustered, and most of them have
irregular morphologies on the ACS images. They have a median reddening of
E(B-V)~0.28, an average star formation rate of ~36 M_sun/yr and a typical
stellar mass of 10^10 M_sun. The UV criterion for the galaxies at z~2 can
select most of the faint sBzKs in the UDF, but it does not work well for
bright, massive, highly-reddened, actively star-forming galaxies.
We have conducted a differential elemental abundance analysis of
unprecedented accuracy (0.01 dex) of the Sun relative to 11 solar twins from
the Hipparcos catalogue and 10 solar analogs from planet searches. We find that
the Sun shows a characteristic signature with a
~20% depletion of refractory elements relative to the volatile elements in
comparison with the solar twins. The abundance differences correlate strongly
with the condensation temperatures of the elements. This peculiarity also holds
in comparisons with solar analogs known to have close-in giant planets while
the majority of solar analogs found not to have such giant planets in radial
velocity monitoring show the solar abundance pattern. We discuss various
explanations for this peculiarity, including the possibility that the
differences in abundance patterns are related to the formation of planetary
systems like our own, in particular to the existence of terrestrial planets.
This paper checks on the roles of metallicity and evolutionary age in the appearance of the so-called Be phenomenon. Slitless CCD spectra were obtained covering the bulk of the Small Magellanic Cloud. For Halpha line emission twice as strong as the ambient continuum, the survey is complete to spectral type B2/B3 on the main sequence. About 8120 spectra of 4437 stars were searched for emission lines in 84 open clusters. 370 emission-line stars were found, among them at least 231 near the main sequence. For 176 of them, photometry could be found in the OGLE database. For comparison with a higher-metallicity environment, the Galactic sample of the photometric Halpha survey by McSwain & Gies (2005) was used. Among early spectral sub-types, Be stars are more frequent by a factor 3-5 in the SMC than in the Galaxy. The distribution with spectral type is similar in both galaxies, i.e. not strongly dependent on metallicity. The fraction of Be stars does not seem to vary with local star density. The Be phenomenon mainly sets in towards the end of the main-sequence evolution (this trend may be more pronounced in the SMC); but some Be stars already form with Be-star characteristics. In all probability, the fractional critical angular rotation rate, \omc, is one of the main parameters governing the occurrence of the Be phenomenon. If the Be character is only acquired during the course of evolution, the key circumstance is the evolution of \omc, which not only is dependent on metallicity but differently so for different mass ranges.
Aims: we seek to provide additional tests of the line formation of theoretical 3D solar photosphere models. In particular, we set out to test the spatially-resolved line formation at several viewing angles, from the solar disk-centre to the limb and focusing on atomic oxygen lines. The purpose of these tests is to provide additional information on whether the 3D model is suitable to derive the solar oxygen abundance. We also aim to empirically constrain the NLTE recipes for neutral hydrogen collisions, using the spatially-resolved observations of the OI 777 nm lines. Methods: using the Swedish 1-m Solar Telescope we obtained high-spatial-resolution observations of five atomic oxygen lines (along with lines for other species) for five positions on the solar disk. These observations have a high spatial and spectral resolution, and a continuum intensity contrast up to 9% at 615 nm. The theoretical line profiles were computed using the 3D model, with a full 3D NLTE treatment for oxygen and LTE for the other lines. Results: at disk-centre we find an excellent agreement between predicted and observed line shifts, strengths, FWHM and asymmetries. At other viewing angles the agreement is also good, but the smaller continuum intensity contrast makes a quantitative comparison harder. We use the disk-centre observations we constrain S_H, the scaling factor for the efficiency of collisions with neutral hydrogen. We find that S_H=1 provides the best match to the observations. Conclusions: overall there is a very good agreement between predicted and observed line properties over the solar granulation. This further reinforces the view that the 3D model is realistic and a reliable tool to derive the solar oxygen abundance.
Context: There is a lively debate about the solar oxygen abundance and the role of 3D models in its recent downward revision. The models have been tested using high resolution solar atlases. Further testing can be done using centre-to-limb variations. Aims: Using high quality observations of oxygen lines across the solar surface we seek to test if the 3D and 1D models reproduce their observed centre-to-limb variation (CLV). In particular we seek to assess whether the 3D model is appropriate to derive the solar oxygen abundance. Methods: We use our recent observations of OI 777 nm, OI 615.81 nm, [OI] 630.03 nm and nine lines of other elements for five viewing angles 0.2<mu<1 of the quiet solar disk. We compare them with the predicted line profiles from the 3D and 1D models computed using the most up-to-date line formation codes, line data and allowing for departures of LTE. The CLV of the OI 777 nm lines is also used to obtain an empirical correction for the poorly known efficiency of the inelastic collisions with H. Results: The 3D model generally reproduces the CLV observations of the lines very well, particularly the oxygen lines. From the OI 777 nm lines we find that the classical Drawin recipe slightly overestimates H collisions. The limb observations of the OI 615.82 nm line allow us to identify a previously unknown contribution of molecules for this line, prevalent at the solar limb. A detailed treatment of the [OI] 630.03 nm line shows that the 3D modeling provides an excellent agreement with the observations. The derived oxygen abundances with the 3D model are 8.68 (OI 777 nm), 8.66 ([OI] 630.03 nm) and 8.62 (OI 615.82 nm). Conclusions: These additional tests have reinforced the trustworthiness of the 3D model and line formation for abundance analyses.
We present Plateau de Bure interferometer observations obtained in continuum at 1.3 and 3.5 mm towards the six most massive and young (IR-quiet) dense cores in Cygnus X. Located at only 1.7 kpc, the Cygnus X region offers the opportunity of reaching small enough scales (of the order of 1700 AU at 1.3 mm) to separate individual collapsing objects. The cores are sub-fragmented with a total of 23 fragments inside 5 cores. Only the most compact core, CygX-N63, could actually be a single massive protostar with an envelope mass as large as 60 Msun. The fragments in the other cores have sizes and separations similar to low-mass pre-stellar and proto-stellar condensations in nearby protoclusters, and are probably of the same nature. A total of 9 out of these 23 protostellar objects are found to be probable precursors of OB stars with envelope masses ranging from 6 to 23 Msun. The level of fragmentation is globally higher than in the turbulence regulated, monolithic collapse scenario, but is not as high as expected in a pure gravo-turbulent scenario where the distribution of mass is dominated by low-mass protostars/stars. Here, the fractions of the total core masses in the high-mass fragments are reaching values as high as 28, 44, and 100 % in CygX-N12, CygX-N53, and CygX-N63, respectively, much higher than what an IMF-like mass distribution would predict. The increase of the fragmentation efficiency as a function of density in the cores is proposed to be due to the increasing importance of self-gravity leading to gravitational collapse at the scale of the dense cores. At the same time, the cores tend to fragment into a few massive protostars within their central regions. We are therefore probably witnessing here the primordial mass segregation of clusters in formation.
In spite of significant recent and ongoing research efforts, most of the early evolution and long-term fate of young massive star clusters remain clouded in uncertainties. Here, I discuss our understanding of the initial conditions of star cluster formation and the importance of initial substructure for the subsequent dynamical-evolution and mass-segregation timescales. I also assess our current understanding of the (initial) binary fraction in star clusters and the shape of the stellar initial mass function at the low-mass end in the low-metallicity environment of the Large Magellanic Cloud. Finally, I question the validity of our assumptions leading to dynamical cluster mass estimates. I conclude that it seems imperative that observers, modellers and theorists combine efforts and exchange ideas and data freely for the field to make a major leap forward.
We investigate wave propagation and energy transport in magnetic elements, which are representatives of small scale magnetic flux concentrations in the magnetic network on the Sun. This is a continuation of earlier work by Hasan et al. (2005). The new features in the present investigation include a quantitative evaluation of the energy transport in the various modes and for different field strengths, as well as the effect of the boundary-layer thickness on wave propagation. We carry out 2-D MHD numerical simulations of magnetic flux concentrations for strong and moderate magnetic fields. Waves are excited in the tube and ambient medium by a transverse impulsive motion of the lower boundary. The nature of the modes excited depends on the value of $\beta$. Mode conversion occurs in the moderate field case when the fast mode crosses the $\beta=1$ contour. In the strong field case the fast mode undergoes conversion from predominantly magnetic to predominantly acoustic when waves are leaking from the interior of the flux concentration to the ambient medium. We also estimate the energy fluxes in the acoustic and magnetic modes. The main conclusions of our work are twofold: firstly, for transverse, impulsive excitation, flux tubes/sheets with strong fields are more efficient than those with weak fields in providing acoustic flux to the chromosphere. However, there is insufficient energy in the acoustic flux to balance the chromospheric radiative losses in the network, even for the strong field case. Secondly, the acoustic emission from the interface between the flux concentration and the ambient medium decreases with the width of the boundary layer.
Giant radio halos are diffuse, Mpc-scale, synchrotron sources located in the central regions of galaxy clusters and provide the most relevant example of cluster non-thermal activity. Radio and X-ray surveys allow to investigate the statistics of halos and may contribute to constrain their origin and evolution. We investigate the distribution of clusters in the plane X-ray (thermal, L_X) vs synchrotron (P_{1.4})luminosity, where clusters hosting giant radio halos trace the P_{1.4}--L_X correlation and clusters without radio halos populate a region that is well separated from that spanned by the above correlation. The connection between radio halos and cluster mergers suggests that the cluster Mpc-scale synchrotron emission is amplified during these mergers and then suppressed when clusters become more dynamically relaxed. In this context, by analysing the distribution in the P_{1.4}--L_X plane of clusters from X-ray selected samples with adequate radio follow up, we constrain the typical time-scale of evolution of diffuse radio emission in clusters and discuss the implications for the origin of radio halos. We conclude that cluster synchrotron emission is suppressed (and amplified) in a time-scale significantly smaller than 1 Gyr. We show that this constraint appears difficult to reconcile with the hypothesis that the halo's radio power is suppressed due to dissipation of magnetic field in galaxy clusters. On the other hand, in agreement with models where turbulent acceleration plays a role, present constraints suggest that relativistic electrons are accelerated in Mpc-scale regions, in connection with cluster mergers and for a time-interval of about 1 Gyr, and then they cool in a relatively small time-scale, when the hosting cluster becomes more dynamically relaxed.
(ABRIDGED) We report here our mapping of the magnetic field topology of the M4 dwarf G 164-31 (or Gl 490B), which is expected to be fully convective, based on time series data collected from 20 hours of observations spread over 3 successive nights with the ESPaDOnS spectropolarimeter. Our tomographic imaging technique applied to time series of rotationally modulated circularly polarized profiles reveals an axisymmetric large-scale poloidal magnetic field on the M4 dwarf. We then apply a synthetic spectrum fitting technique for measuring the average magnetic flux on the star. The flux measured in G 164-31 is Bf = 3.2+-0.4 kG, which is significantly greater than the average value of 0.68 kG determined from the imaging technique. The difference indicates that a significant fraction of the stellar magnetic energy is stored in small-scale structures at the surface of G 164-31. Our H_alpha emission light curve shows evidence for rotational modulation suggesting the presence of localized structure in the chromosphere of this M dwarf. The radius of the M4 dwarf derived from the rotational period and the projected equatorial velocity is at least 30% larger than that predicted from theoretical models. We argue that this discrepancy is likely primarily due to the young nature of G 164-31 rather than primarily due to magnetic field effects, indicating that age is an important factor which should be considered in the interpretation of this observational result. We also report here our polarimetric observations of five other M dwarfs with spectral types from M0 to M4.5, three of them showing strong Zeeman signatures.
In this paper we consider the re-processing of high frequency photons emitted by HeII and HeI during the epoch of cosmological recombination by HeI and HI. We demonstrate that, in comparison to computations which neglect all feedback processes, the number of cosmological recombination photons that are related to the presence of helium in the early Universe could be increased by ~40%-70%. Our computations imply that per helium nucleus ~3-6 additional photons could be produced. Therefore, a total of ~12-14 helium-related photons are emitted during cosmological recombination. This is an important addition to cosmological recombination spectrum which in the future may render it slightly easier to determine the primordial abundance of helium using differential measurements of the CMB energy spectrum. Also, since these photons are the only witnesses of the feedback process at high redshift, observing them in principle offers a way to check our understanding of the recombination physics. Here most interestingly, the feedback of HeII photons on HeI leads to the appearance of several additional, rather narrow spectral features in the HeI recombination spectrum at low frequencies. Consequently, the signatures of helium-related features in the CMB spectral distortion due to cosmological recombination at some given frequency can exceed the average level of ~17% several times. We find that in particular the bands around nu ~10GHz, ~35GHz, ~80GHz, and ~200GHz seem to be affected strongly. In addition, we computed the changes in the cosmological ionization history, finding that only the feedback of primary HeI photons on the dynamics of HeII-->HeI recombination has an effect, producing a change of DN_e/N_e ~+ 0.17% at z~2300. This result seems to be ~2-3 times smaller than the one obtained in earlier computations for this process (abridged).
We present results using the AutoClass analysis application available at NASA/Ames Intelligent Systems Div. (2002) which is a Bayesian, finite mixture model classification system developed by Cheeseman and Stutz (1996). We apply this system to Mount Wilson Solar Observatory (MWO) intensity and magnetogram images and classify individual pixels on the solar surface to calculate daily indices that are then correlated with total solar irradiance (TSI) to yield a set of regression coefficients. This approach allows us to model the TSI with a correlation of better than 0.96 for the period 1996 to 2007. These regression coefficients applied to classified pixels on the observed solar surface allow the construction of images of the Sun as it would be seen by TSI measuring instruments like the Solar Bolometric Imager recently flown by Foukal et al., (2004). As a consequence of the very high correlation we achieve in reproducing the TSI record, our approach holds out the possibility of creating an on-going, accurate, independent estimate of TSI variations fromground-based observations which could be used to compare, and identify the sources of disagreement among, TSI observations from the various satellite instruments and to fill in gaps in the satellite record. Further, our spatially-resolved images should assist in characterizing the particular solar surface regions associated with TSI variations. Also, since the particular set of MWO data on which this analysis is based is available on a daily basis back to at least 1985, and on an intermittent basis before then, it will be possible to estimate the TSI emission due to identified solar surface features at several solar minima to constrain the role surface magnetic effects have on long-term trends in solar energy output.
We study a model of weakly ionized, protostellar accretion discs that are threaded by a large-scale, ordered magnetic field and power a centrifugally driven wind. We consider the limiting case where the wind is the main repository of the excess disc angular momentum and generalize the radially localized disc model of Wardle & K\"onigl (1993), which focussed on the ambipolar diffusion regime, to other field diffusivity regimes, notably Hall and Ohm. We present a general formulation of the problem for nearly Keplerian, vertically isothermal discs using both the conductivity-tensor and the multi-fluid approaches and simplify it to a normalized system of ordinary differential equations in the vertical space coordinate. We determine the relevant parameters of the problem and investigate, using the vertical-hydrostatic-equilibrium approximation and other simplifications, the parameter constraints on physically viable solutions for discs in which the neutral particles are dynamically well coupled to the field already at the midplane. When the charged particles constitute a two-component ion--electron plasma one can identify four distinct sub-regimes in the parameter domain where the Hall diffusivity dominates and three sub-regimes in the Ohm-dominated domain. Two of the Hall sub-regimes can be characterized as being ambipolar diffusion-like and two as being Ohm-like. When the two-component plasma consists instead of positively and negatively charged grains of equal mass, the entire Hall domain and one of the Ohm sub-regimes disappear. In all viable solutions the midplane neutral--ion momentum exchange time is shorter than the local orbital time. Vertical magnetic squeezing always dominates over gravitational tidal compression in this model. (Abridged)
We present the results of a systematic search for galaxies in the redshift range z = 6 - 9, within the new, deep, near-infrared imaging of the Hubble Ultra Deep Field provided by the Wide Field Camera 3 (WFC3) on HST. We have performed full SED fitting to the optical+infrared photometry of all high-redshift galaxy candidates detected at greater than 5-sigma in at least one of the WFC3/IR broad-band filters. After rejection of contaminants, the result is a sample of 49 galaxies with primary redshift solutions z > 5.9. Our sample, selected without recourse to specific colour cuts, re-selects all but the faintest one of the 16 z-drops selected by Oesch et al. (2009), recovers all 5 of the Y-drops reported by Bouwens et al. (2009), and adds a further 29 galaxy candidates, of which 12 lie beyond z = 6.3, and 4 lie beyond z = 7. We also present confidence intervals on our photometric redshift estimates, and caution that acceptable low-redshift (z < 2) solutions exist for 28 out of the 37 galaxies at z > 6.3, and for all 8 galaxy candidates at z > 7.5. Nevertheless, the very highest redshift candidates appear to be strongly clustered in the field. We derive new estimates of the ultraviolet galaxy luminosity function at z = 7 and z = 8. Where our results are most robust, at a characteristic luminosity M(1500) ~ -19.5 (AB), we find that the comoving number density of galaxies declines by a factor of ~ 2.5 between z = 6 and z = 7, and by a further factor of ~ 2 by z = 8. These results suggest that it is difficult for the observed population of high-redshift star-forming galaxies to achieve reionisation by z ~ 6 without a significant contribution from galaxies well below the detection limits, plus alterations in the escape fraction of ionising photons and/or continued vigorous star formation at z > 15.
Radio pulsars emit regular bursts of radio radiation that propagate through the interstellar medium (ISM), the tenuous gas and plasma between the stars. Previously known dispersive properties of the ISM cause low frequency pulses to be delayed in time with respect to high frequency ones. This effect can be explained by the presence of free electrons in the medium. The ISM also contains neutral hydrogen which has a well known resonance at 1420.4 MHz. Electro-magnetic theory predicts that at such a resonance, the induced dispersive effects will be drastically different from those of the free electrons. Pulses traveling through a cloud of neutral hydrogen should undergo "anomalous dispersion", which causes the group velocity of the medium to be larger than the speed of light in vacuum. This superluminal group velocity causes pulses containing frequencies near the resonance to arrive earlier in time with respect to other pulses. Hence, these pulses appear to travel faster than light. This phenomenon is caused by an interplay between the time scales present in the pulse and the time scales present in the medium. Although counter-intuitive, it does not violate the laws of special relativity. Here, we present Arecibo observations of the radio pulsar PSR B1937+21 that show clear evidence of anomalous dispersion. Though this effect is known in laboratory physics, this is the first time it has been directly observed in an astrophysical context, and it has the potential to be a useful tool for studying the properties of neutral hydrogen in the Galaxy.
We present a study of the intermediate regime between ultra-relativistic and nonrelativistic flow for gamma-ray burst afterglows. The hydrodynamics of spherically symmetric blast waves is numerically calculated using the AMRVAC adaptive mesh refinement code. Spectra and light curves are calculated using a separate radiation code that, for the first time, links a parametrisation of the microphysics of shock acceleration, synchrotron self-absorption and electron cooling to a high-performance hydrodynamics simulation. For the dynamics we find that the transition to the nonrelativistic regime generally occurs later than expected, that the Sedov-Taylor solution overpredicts the late time blast wave radius and that the analytical formula for the blast wave velocity from Huang (1999) overpredicts the late time velocity by a factor 4/3. For the radiation we find that the flux may differ up to an order of magnitude depending on the equation of state that is used for the fluid and that the counterjet leads to a clear rebrightening at late times for hard-edged jets. Simulating GRB030329 using predictions for its physical parameters from the literature leads to spectra and light curves that may differ significantly from the actual data, emphasizing the need for very accurate modelling. Predicted light curves at low radio frequencies for a hard-edged jet model of GRB030329 with opening angle 22 degrees show typically two distinct peaks, due to the combined effect of jet break, non relativistic break and counterjet.
The deepest multi-wavelength surveys now provide measurements of star
formation in galaxies out to z>1, and allow to reconstruct its history for
large parts of the galaxy population. I review recent studies, which have
consistently revealed a picture where galaxy star formation rates and their
evolution are primarily determined by galaxy mass. Unless they undergo a
quenching of their star formation, galaxies of similar masses have very similar
star formation histories, which turn out to be relatively smooth: star
formation rates decline with redshift in a primarily gradual manner, while
typical starburst episodes have only a modest amplitude that barely evolves.
I discuss how the found relations and their redshift evolution can provide an
observed reference star formation history as a function of galaxy mass.
The observed amplitudes and timescales of galaxy star formation are not fully
reproduced by current theoretical models, and are a promising testbed to
improve the assumed baryon physics. However, measurements of star formation
rates in distant galaxies need to be treated with caution. Near-future data,
methods and instruments will help us to improve on calibrations and
sensitivities for high redshift star formation.
We report evidence for an anti-correlation between spin temperature $T_s$ and metallicity [Z/H], detected at $3.6 \sigma$ significance in a sample of 26 damped Lyman-$\alpha$ absorbers (DLAs) at redshifts $0.09 < z < 3.45$. The anti-correlation is detected at $3 \sigma$ significance in a sub-sample of 20 DLAs with measured covering factors, implying that it does not stem from low covering factors. We obtain $T_s = (-0.68 \pm 0.17) \times {\rm [Z/H]} + (2.13 \pm 0.21)$ from a linear regression analysis. Our results indicate that the high $T_s$ values found in DLAs do not arise from differences between the optical and radio sightlines, but are likely to reflect the underlying gas temperature distribution. The trend between $T_s$ and [Z/H] can be explained by the larger number of radiation pathways for gas cooling in galaxies with high metal abundances, resulting in a high cold gas fraction, and hence, a low spin temperature. Conversely, low-metallicity galaxies have fewer cooling routes, yielding a larger warm gas fraction and a high $T_s$. Most DLAs at $z>1.7$ have low metallicities, [Z/H] $< -1$, implying that the HI in high-$z$ DLAs is predominantly warm. The anti-correlation between $T_s$ and [Z/H] is consistent with the presence of a mass-metallicity relation in DLAs, suggested by the tight correlation between DLA metallicity and the kinematic widths of metal lines. Most high-$z$ DLAs are likely to arise in galaxies with low masses ($M_{\rm vir} < 10^{10.5} M_\odot$), low metallicities ([Z/H]$< -1$, and low cold gas fractions.
In this paper we investigate the use of the vector potential as a means of
maintaining the divergence constraint in the numerical solution of the
equations of Magnetohydrodynamics (MHD) using the Smoothed Particle
Hydrodynamics (SPH) method. We derive a self-consistent formulation of the
equations of motion using a variational principle that is constrained by the
numerical formulation of both the induction equation and the curl operator used
to obtain the magnetic field, which guarantees exact and simultaneous
conservation of momentum, energy and entropy in the numerical scheme. This
leads to a novel formulation of the MHD force term, unique to the vector
potential, which differs from previous formulations. We also demonstrate how
dissipative terms can be correctly formulated for the vector potential such
that the contribution to the entropy is positive definite and the total energy
is conserved.
On a standard suite of numerical tests in one, two and three dimensions we
find firstly that the consistent formulation of the vector potential equations
is unstable to the well-known SPH tensile instability, even more so than in the
standard Smoothed Particle Magnetohydrodynamics (SPMHD) formulation where the
magnetic field is evolved directly. Furthermore we find that, whilst a hybrid
approach based on the vector potential evolution equation coupled with a
standard force term gives good results for one and two dimensional problems
(where dAz/dt = 0), such an approach suffers from numerical instability in
three dimensions related to the unconstrained evolution of vector potential
components. We conclude that use of the vector potential is not a viable
approach for Smoothed Particle Magnetohydrodynamics.
We report on the observation of the bright, long gamma-ray burst, GRB 090902B, by the Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) instruments on-board the Fermi observatory. This was one of the brightest GRBs to have been observed by the LAT, which detected several hundred photons during the prompt phase. With a redshift of z = 1.822, this burst is among the most luminous detected by Fermi. Time-resolved spectral analysis reveals a significant power-law component in the LAT data that is distinct from the usual Band model emission that is seen in the sub-MeV energy range. This power-law component appears to extrapolate from the GeV range to the lowest energies and is more intense than the Band component both below $\sim$ 50 keV and above 100 MeV. The Band component undergoes substantial spectral evolution over the entire course of the burst, while the photon index of the power-law component remains constant for most of the prompt phase, then hardens significantly towards the end. After the prompt phase, power-law emission persists in the LAT data as late as 1 ks post-trigger, with its flux declining as $t^{-1.5}$. The LAT detected a photon with the highest energy so far measured from a GRB, $33.4_{-3.5}^{+2.7}$ GeV. This event arrived 82 seconds after the GBM trigger and $\sim$ 50 seconds after the prompt phase emission had ended in the GBM band. We discuss the implications of these results for models of GRB emission and for constraints on models of the Extragalactic Background Light.
With the availability of the large database of black-hole transients from the Rossi X-Ray Timing Explorer, the observed phenomenology has become very complex. The original classification of the properties of these systems in a series of static states sorted by mass accretion rate proved not to be able to encompass the new picture. I outline here a summary of the current situation and show that a coherent picture emerges when simple properties such as X-ray spectral hardness and fractional variability are considered. In particular, fast transition in the properties of the fast time variability appear to be crucial to describe the evolution of black-hole transients. Based on this picture, I present a state-classification which takes into account the observed transitions. I show that, in addition to transients systems, other black-hole binaries and Active Galactic Nuclei can be interpreted within this framework. The association between these states and the physics of the accretion flow around black holes will be possible only through modeling of the full time evolution of galactic transient systems.
We present results of thermal evolution calculations for objects originating in the Kuiper belt and transferring inwards, to the region of the outer planets. Kuiper belt objects (KBOs) are considered to be part of a reservoir that supplies the flux of small icy bodies, mainly Centaurs and Jupiter-family comets, to regions interior to the orbit of Neptune. We study the internal thermal evolution, for yr, of three typical KBOs and use the end state of the simulation as initial conditions for evolutionary calculations of two typical Centaurs. Some evolutionary trends can be identified for the KBOs, depending on key physical parameters, such as size and composition. The subsequent evolution in the Centaur region results in both specific features for each modeled object (mainly surface and sub-surface composition) and common characteristics of thermally evolved Centaurs.
We introduce a new technique, called the Sliding Two-Dimensional Fluctuation Spectrum, used for detecting and characterising the temporal changes of drifting subpulses from radio pulsars. The method was tested using simulated data as well as archived observations made with the WSRT at wavelengths of 92 and 21 cm. The drifting subpulse phenomenon is a well known property of radio pulsars. However the properties of the temporal behaviour of drifting subpulses are not fully explored. The drifting can also be non-coherent and the presence of effects like nulling or drift rate changing can mask the drifting behaviour of the pulsar. The S2DFS is a robust method for investigating this phenomenon and by introducing it we aim to expand our knowledge of the temporal drifting subpulse properties. Our new analysis method uses horizonally collapsed fluctuation spectra obtained with the Two-Dimensional Fluctuation Spectrum method. Stacking the collapsed spectra obtained in a 256 pulse window which slides by a pulse at a time produces a map of the collapsed fluctuation spectrum. By analysing the maps one can easily determine the presence of any temporal drift changes. Simulated data showed that the technique can reveal the presence of any temporal changes in drift behaviour like mode changing or nulling. We have also analysed data of three pulsars, PSRs B0031-07, B1819-22 and B1944+17, which were selected based on the quality of the data and their known drift properties. All three sources are known to exhibit mode changes which could easily be seen in the S2DFS. The results from the analysis of the data sets used in this paper have shown that the S2DFS method is robust and complimentary to the 2DFS method in detecting and characterising the temporal changes in drifting subpulses from radio pulsars.
In a flat universe dominated by dark energy, the Integrated Sachs-Wolfe (ISW) effect can be detected as a large-angle cross-correlation between the CMB and a tracer of large scale structure. We investigate whether the inconclusive ISW signal derived from 2MASS galaxy maps can be improved upon by including photometric redshifts for the 2MASS galaxies. These redshifts are derived by matching the 2MASS data with optical catalogues generated from SuperCOSMOS scans of major photographic sky surveys. We find no significant ISW signal in this analysis; an ISW effect of the form expected in a LambdaCDM Universe is only weakly preferred over no correlation, with a likelihood ratio of 1.5:1. We consider ISW detection prospects for future large scale structure surveys with fainter magnitude limits and greater survey depth; even with the best possible data, the ISW cross-correlation signal would be expected to evade detection in >~ 10% of cases.
We estimate the local density field in redshift shells to a maximum redshift of z=0.3, using photometric redshifts for the 2MASS galaxy catalogue, matched to optical data from the SuperCOSMOS galaxy catalogue. This density-field map is used to predict the Integrated Sachs-Wolfe (ISW) CMB anisotropies that originate within the volume at z<0.3. We investigate the impact of this estimated ISW foreground signal on large-scale anomalies in the WMAP CMB data. We find that removal of the foreground ISW signal from WMAP data reduces the significance of a number of reported large-scale anomalies in the CMB, including the low quadrupole power and the apparent alignment between the CMB quadrupole and octopole.
Coalescing neutron star binaries are believed to be the most reliable sources for ground-based detectors of gravitational waves and likely progenitors of short gamma-ray bursts. In the process of coalescence, magnetic fields of neutron stars can induce interesting observational manifestations and affect the form of gravitational wave signal. In this papaer we use the population synthesis method to model the expected distribution of neutron star magnetic fields during the coalescence under different assumptions on the initial parameters of neutron stars and their magnetic field evolution. We discuss possible elecotrmagnetic phenomena preceding the coalescence of magnetized neutron star binaries and the effect of magnetic field on the gravitational wave signal. We find that a log-normal (Gaussian in logarithms) distribution of the initial magnetic fields of neutron stars, which agrees with observed properties of radio pulsars, produces the distribution of the magnetic field energy during the coalescence that adequately describes the observed luminosity function of short gamma-ray bursts under different assumptions on the field evolution and initial parameters of neutron stars. This agreement lends further support to the model of coalescing neutron star binaries as progenitors of gamma-ray bursts.
We use signal enhancement techniques and a matched filter analysis to search for the K band spectroscopic absorption signature of the close orbiting extrasolar giant planet, HD 189733b. With timeseries observations taken with NIRSPEC at the Keck II telescope, we investigate the relative abundances of H2O and carbon bearing molecules, which have now been identified in the dayside spectrum of HD 189733b. We detect a candidate planet signature with a low level of significance, close to the ~153 km/s velocity amplitude of HD 189733b. However, some systematic variations, mainly due to imperfect telluric line removal, remain in the residual spectral timeseries in which we search for the planetary signal. The robustness of our candidate signature is assessed, enabling us to conclude that it is not possible to confirm the presence of any planetary signal which appears at Fp/F* contrasts deeper than the 95.4 per cent confidence level. Our search does not enable us to detect the planet at a contrast ratio of Fp/F* = 1/1920 with 99.9 per cent confidence. We also investigate the effect of model uncertainties on our ability to reliably recover a planetary signal. The use of incorrect temperature, model opacity wavelengths and model temperature-pressure profiles have important consequences for the least squares deconvolution procedure that we use to boost the S/N ratio in our spectral timeseries observations. We find that mismatches between the empirical and model planetary spectrum may weaken the significance of a detection by ~30-60 per cent, thereby potentially impairing our ability to recover a planetary signal with high confidence.
BP Cru is a well known high-mass X-ray binary composed of a late B hypergiant (Wray 977) and a neutron star, also observed as the X-ray pulsar GX 301-2. No information about emission from BP Cru in other bands than X-rays and optical has been reported to date in the literature, though massive X-ray binaries containing black holes can have radio emission from a jet. In order to assess the presence of a radio jet, we searched for radio emission towards BP Cru using the Australia Compact Array Telescope during a survey for radio emission from Be/X-ray transients. We probed the 41.5d orbit of BP Cru with the Australia Telescope Compact Array not only close to periastron but also close to apastron. BP Cru was clearly detected in our data on 4, possibly 6, of 12 occasions at 4.8 and 8.6 GHz. Our data suggest that the spectral index of the radio emission is modulated either by the X-ray flux or the orbital phase of the system. We propose that the radio emission of BP Cru probably arises from two components: a persistent component, coming from the mass donor Wray 977, and a periodic component connected to the accretion onto the neutron star, possibly coming from a (weak and short lived) jet.
Aims. We aim here to contribute to the identification of unassociated bright
sources of gamma-rays in the recently released catalogue obtained by the Fermi
collaboration.
Methods. Our work is based on a extensive cross-identification of sources
from different wavelength catalogues and databases.
Results. As a first result, we report the finding of a few counterpart
candidates inside the 95% confidence error box of the Fermi LAT unidentified
gamma-ray source 0FGL J1848.6$-$0138. The globular cluster GLIMPSE-C01
remarkably stands out among the most peculiar objects consistent with the
position uncertainty of the gamma-ray source and with a conceivable physical
scenario for gamma-ray production. The Fermi observed spectrum is compared
against theoretical predictions in the literature making the association
plausible but not yet certain due to its low X-ray to gamma-ray luminosity
ratio. Other competing counterparts are also discussed. In particular, we pay a
special attention to a possible Pulsar Wind Nebula inside the Fermi error box
whose nature is yet to be confirmed.
Conclusions.Both a globular cluster and an infrared source resembling a
Pulsar Wind Nebula have been found in positional agreement with 0FGL
J1848.6$-$0138. In addition, other interesting objects in the field are also
reported. Future gamma-ray observations will narrow the position uncertainty
and we hope to eventually confirm one of the counterpart candidates reported
here. If GLIMPSE-C01 is confirmed, together with the Fermi possible detection
of the well known globular cluster 47 Tuc, then it would provide strong support
to theoretical predictions of globular clusters as gamma-ray sources.
We compare observations of the non-flaring solar corona made simultaneously with Hinode/XRT and with RHESSI. The analyzed corona is dominated by a single active region on 12 November 2006. The comparison is made on emission measures. We derive emission measure distributions vs temperature of the entire active region from multifilter XRT data. We check the compatibility with the total emission measure values estimated from the flux measured with RHESSI if the emission come from isothermal plasma. We find that RHESSI and XRT data analyses consistently point to the presence of a minor emission measure component peaking at log T ~ 6.8-6.9. The discrepancy between XRT and RHESSI results is within a factor of a few and indicates an acceptable level of cross-consistency.
We present a catalog of optical spectroscopic identifications of sources detected by Spitzer at 3.6 or 24 micron down to 10 and 280 microJy, respectively, in the SWIRE/XMM-Newton/ELAIS-S1 field and classified via line width analysis and diagnostic diagrams. A total of 1376 sources down to R~24.2 mag have been identified (1362 detected at 3.6 micron, 419 at 24 micron, and 405 at both) by low-resolution optical spectroscopy carried out with FORS2, VIMOS, and EFOSC2 at the Very Large Telescope and 3.6m ESO telescopes. The spectroscopic campaigns have been carried out over the central 0.6 square degrees area of ELAIS-S1 which, in particular, has also been observed by XMM-Newton and Chandra. We find the first direct optical spectroscopic evidence that the fraction of active galactic nuclei (AGN; mostly AGN2) increases with increasing F(24 micron)/F(R) ratio, reaching values of 70(+/-20)% in the range 316<F(24 micron)F(R)<1000. We present an IRAC-MIPS color-color diagram able to separate AGN1 from obscured AGN2 candidates. After having corrected for the spectroscopic incompleteness of our sample, it results that the AGN fraction at F(24 micron)=0.8 mJy is ~22(+/-7)% and decreases slowly to ~19(+/-5)% down to F(24 micron)=0.3 mJy.
We demonstrate the newly developed resource for exoplanet researchers - The Exoplanet Transit Database. This database is designed to be a web application and it is open for any exoplanet observer. It came on-line in September 2008. The ETD consists of three individual sections. One serves for predictions of the transits, the second one for processing and uploading new data from the observers. We use a simple analytical model of the transit to calculate the central time of transit, its duration and the depth of the transit. These values are then plotted into the observed - computed diagrams (O-C), that represent the last part of the application.
Masses are a fundamental parameter, but they are not well known for most hot subdwarfs. In general, the mass of a hot subdwarf is derived with asteroseismology or dynamical methods, for which it is often difficult to obtain the necessary data from observations. We intend to find an approach to deriving the masses of hot subdwarfs from observational data in the literature. We presented full evolutionary calculations for hot subdwarfs in a wide mass range (0.33 $M_\odot$ to 1.4 $M_\odot$) for a Population I metallicity of $Z$=0.02, and obtained a relation between $M_{\rm p}$ and $\log (\frac{T_{\rm eff}^4}{g})$, where $M_{\rm p}$, $T_{\rm eff}$, and $g$ are the most probable mass, effective temperature, and gravity. This relation is used to study the masses of some observed hot subdwarfs. We proposed a method of determining the masses of hot subdwarfs. Using this method, we studied the masses of hot subdwarfs from the ESO supernova Ia progenitor survey and Hamburg quasar survey. The study shows that most of subdwarf B stars have masses between 0.42 and 0.54 $M_\odot$, whilst most sdO stars are in the range 0.40 $\sim$ 0.55 $M_\odot$. Comparing our study to the theoretical mass distributions of Han et al. (2003), we found that sdO stars with mass less than $\sim$ 0.5 $M_\odot$ may evolve from sdB stars, whilst most high-mass($>$ 0.5 $M_\odot$) sdO stars result from mergers directly.
The properties of X-ray emission from accreting black holes are reviewed. The contemporary observational picture and current status of theoretical understanding of accretion and formation of X-ray radiation in the vicinity of the compact object are equally in the focus of this chapter. The emphasis is made primarily on common properties and trends rather than on peculiarities of individual objects and details of particular theoretical models. The chapter starts with discussion of the geometry of the accretion flow, spectral components in X-ray emission and black hole spectral states. The prospects and diagnostic potential of X-ray polarimetry are emphasized. Significant attention is paid to the discussion of variability of X-ray emission in general and of different spectral components -- emission of the accretion disk, Comptonized radiation and reflected component. Correlations between spectral and timing characteristics of X-ray emission are reviewed and discussed in the context of theoretical models. Finally, a comparison with accreting neutron stars is made.
In this chapter I will review the status of our phenomenological understanding of the relation between accretion and outflows in accreting black hole systems. This understanding arises primarily from observing the relation between X-ray and longer wavelength (infrared, radio) emission. The view is necessarily a biased one, beginning with observations of X-ray binary systems, and attempting to see if they match with the general observational properties of active galactic nuclei.
A solid theoretical understanding of how inflowing, accreting plasma around black holes and other compact objects gives rise to outflowing winds and jets is still lacking, despite decades of observations. The fact that similar processes and morphologies are observed in both X-ray binaries as well as active galactic nuclei has led to suggestions that the underlying physics could scale with black hole mass, which could provide a new handle on the problem. In the last decade, simultaneous broadband campaigns of the fast-varying X-ray binaries particularly in their microquasar state have driven the development of, and in some cases altered, our ideas about the inflow/outflow connection in accreting black holes. Specifically the discovery of correlations between the radio, infrared and X-ray bands has revealed a remarkable connectivity between the various emission regions, and argued for a more holistic approach to tackling questions about accretion. This article reviews the recent major observational and theoretical advances that focus specifically on the relation between the two "sides" of the accretion process in black holes, with an emphasis on how new tools can be derived for comparisons across the mass scale.
We point out a strong time-evolution of the mass-to-light conversion factor eta commonly used to estimate masses of unresolved star clusters from observed cluster spectro-photometric measures. We present a series of gas-dynamical models coupled with the Cambridge stellar evolution tracks to compute line-of-sight velocity dispersions and half-light radii weighted by the luminosity. We explore a range of initial conditions, varying in turn the cluster mass and/or density, and the stellar population's IMF. We find that eta, and hence the estimated cluster mass, may increase by factors as large as 3 over time-scales of 50 million years. We apply these results to an hypothetic cluster mass distribution function (d.f.) and show that the d.f. shape may be strongly affected at the low-mass end by this effect. Fitting truncated isothermal (Michie-King) models to the projected light profile leads to over-estimates of the concentration parameter c of delta c ~ 0.3 compared to the same functional fit applied to the projected mass density.
The jets of active galactic nuclei can carry a large fraction of the accreted power of the black-hole system into interstellar and even extragalactic space. They radiate profusely from radio to X-ray and gamma-ray frequencies. In the most extreme cases, the outward flow speeds correspond to high Lorentz factors that can reach 40 or more. This chapter displays images at various wavebands as well as light curves and continuum spectra that illustrate the variability with location, time, and frequency of the emission from compact, parsec- and subparsec-scale jets. It presents a physical framework for investigating many aspects of the structure and dynamical processes from such data.
The gas in the cores of many clusters and groups of galaxies has a short radiative cooling time. Energy from the central black hole is observed to flow into this gas by means of jets, bubbles and sound waves. Cooling is thus offset by heating. We discuss the mechanisms involved and observed in the X-ray brightest clusters and explore the closeness of the heating/cooling balance. It is surprisingly tight on the cooling side when soft X-ray spectra are examined. Non-radiative cooling by mixing is suggested as a means to relax the apparent strong lack of cooling. Nevertheless the heating and cooling must balance on average to better than 20 per cent.
Over the last 12 years, AGN monitoring by RXTE, has revolutionised our understanding of the X-ray variability of AGN, of the relationship between AGN and Galactic black hole X-ray binaries (BHBs) and hence of the accretion process itself, which fuels the emission in AGN and BHBs and is the major source of power in the universe. In this paper I review our current understanding of these topics. I begin by considering whether AGN and BHBs show the same X-ray spectral-timing `states' (e.g. low-flux, hard-spectrum or `hard' and high-flux, soft-spectrum or `soft'). Observational selection effects mean that most of the AGN which we have monitored will probably be `soft state' objects, but AGN are found in the other BHB states, although possibly with different critical transition accretion rates. I examine timescale scaling relationships between AGN and BHBs. I show that characteristic power spectral `bend' timescales, T_B, scale approximately with black hole mass, M_BH, but inversely with accretion rate, mdot_E, (in units of the Eddington accretion rate) probably signifying that T_B, arises at the inner edge of the accretion disc. The relationship T_B proportional to M_BH/mdot_E is a good fit, implying that no other potential variable, e.g. black hole spin, varies significantly. Lags between hard and soft X-ray bands as a function of Fourier timescale follow similar patterns in AGN and BHBs. [Abridged]
Magnetic fields connecting the immediate environs of rotating black holes to large distances appear to be the most promising mechanism for launching relativistic jets, an idea first developed by Blandford and Znajek in the mid-1970s. To enable an understanding of this process, we provide a brief introduction to dynamics and electromagnetism in the spacetime near black holes. We then present a brief summary of the classical Blandford-Znajek mechanism and its conceptual foundations. Recently, it has become possible to study these effects in much greater detail using numerical simulation. After discussing which aspects of the problem can be handled well by numerical means and which aspects remain beyond the grasp of such methods, we summarize their results so far. Simulations have confirmed that processes akin to the classical Blandford-Znajek mechanism can launch powerful electromagnetically-dominated jets, and have shown how the jet luminosity can be related to black hole spin and concurrent accretion rate. However, they have also shown that the luminosity and variability of jets can depend strongly on magnetic field geometry. We close with a discussion of several important open questions.
We show that there is no need for the hypothetical Dark Energy (DE) and Dark Matter (DM) to explain phenomena attributed to them. In contrast to the consensus of the last decade, we show that the time derivative of the cosmological scale factor, is a constant. We derive H(z), the Hubble parameter, as a function of the redshift, z. Based on H(z), we derive a curve of the Distance Modulus versus log(z). This curve fits data from supernovae observations, without any free parameters. This fit is as good as that obtained by current cosmology, which needs the free parameters Omega_M and Omega_Lambda. We obtain these results by using the hitherto un-noticed fact that the global gravitational energy density in our Hubble Sphere (HS) is equal to the Cosmological Microwave Background (CMB) energy density. We derive the dynamic and kinematic relations that govern the motions of celestial bodies in and around galaxies. This derivation does not require any gravitating matter beyond the observed baryonic matter. The theoretical Rotation Curves (RC), resulting from these relations, fit observed RCs. We obtain these results by examining the interplay between the local gravitational energy density, around a galaxy, and the CMB energy density. This interplay causes the inhomogeneous and anisotropic space expansion around a galaxy.
To some extent, all Galactic binary systems hosting a compact object are potential `microquasars', so much as all galactic nuclei may have been quasars, once upon a time. The necessary ingredients for a compact object of stellar mass to qualify as a microquasar seem to be: accretion, rotation and magnetic field. The presence of a black hole may help, but is not strictly required, since neutron star X-ray binaries and dwarf novae can be powerful jet sources as well. The above issues are broadly discussed throughout this Chapter, with a a rather trivial question in mind: why do we care? In other words: are jets a negligible phenomenon in terms of accretion power, or do they contribute significantly to dissipating gravitational potential energy? How do they influence their surroundings? The latter point is especially relevant in a broader context, as there is mounting evidence that outflows powered by super-massive black holes in external galaxies may play a crucial role in regulating the evolution of cosmic structures. Microquasars can also be thought of as a form of quasars for the impatient: what makes them appealing, despite their low number statistics with respect to quasars, are the fast variability time-scales. In the first approximation, the physics of the jet-accretion coupling in the innermost regions should be set by the mass/size of the accretor: stellar mass objects vary on 10^5-10^8 times shorter time-scales, making it possible to study variable accretion modes and related ejection phenomena over average Ph.D. time-scales. [Abridged]
We present analysis of 25 years' worth of archival VLA, VLBA and EVN observations of the X-ray binary Cygnus X-3. From this, we deduce the source proper motion, allowing us to predict the location of the central binary system at any given time. However, the line of sight is too scatter-broadened for us to measure a parallactic distance to the source. The measured proper motion allows us to constrain the three-dimensional space velocity of the system, implying a minimum peculiar velocity of 9 km/s. Reinterpreting VLBI images from the literature using accurate core positions shows the jet orientation to vary with time, implying that the jets are oriented close to the line of sight and are likely to be precessing.
We systematically investigate the error sources for high-precision astrometry from adaptive optics based near-infrared imaging data. We focus on the application in the crowded stellar field in the Galactic Center. We show that at the level of <=100 micro-arcseconds a number of effects are limiting the accuracy. Most important are the imperfectly subtracted seeing halos of neighboring stars, residual image distortions and unrecognized confusion of the target source with fainter sources in the background. Further contributors to the error budget are the uncertainty in estimating the point spread function, the signal-to-noise ratio induced statistical uncertainty, coordinate transformation errors, the chromaticity of refraction in Earth's atmosphere, the post adaptive optics differential tilt jitter and anisoplanatism. For stars as bright as mK=14, residual image distortions limit the astrometry, for fainter stars the limitation is set by the seeing halos of the surrounding stars. In order to improve the astrometry substantially at the current generation of telescopes, an adaptive optics system with high performance and weak seeing halos over a relatively small field (r<=3") is suited best. Furthermore, techniques to estimate or reconstruct the seeing halo could be promising.
The bipolarity of Supernova 1987A can be understood in terms of its very early light curve as observed from the CTIO 0.4-m telescope, as well as the IUE FES, and the slightly later speckle observations of the "Mystery Spot" by two groups. These observations imply a highly directional beam of light and jet of particles, with initial collimation factors in excess of 10,000, velocities in excess of 0.95 c, as an impulsive event involving up to 0.00001 solar masses, which interacts with circumstellar material. The jet and beam coincide with the 194 degree angle of the bipolarity on the sky, and are oriented at 75 degrees to the line of sight to the Earth. By day 30 the collimation of the jet decreases, and its velocity declines to ~0.5 c. These observations and the resulting kinematic solution can be understood in terms of pulsar emission from polarization currents, induced by the periodically modulated electromagnetic field beyond the pulsar light cylinder, which are thus modulated at up to many times the speed of light. With plasma available at many times the light cylinder radius, as would be the case for a spinning neutron star formed at the center of its progenitor, pulsed emission is directed close to the rotation axis, eviscerating this progenitor, and continuing for months to years, until very little circumpulsar material remains. This model provides a candidate for the central engine of the gamma-ray burst (GRB) mechanism, both long and short, and predicts that GRB afterglows are the_pulsed_ optical/near infrared emission associated with these newly-born neutron stars.
The ALFALFA (Arecibo Legacy Fast ALFA) blind survey is providing a census of HI in galaxies of all types in a range of environments. Here we report on ALFALFA results for Virgo Cluster early-type dwarfs between declinations of 4 and 16 degrees. Less than 2% of the Virgo early-type dwarf population is detected, compared to 70-80% of the Im/BCD dwarf population. Most of the dwarfs detected in HI show evidence for ongoing or recent star formation. Early-type galaxies with HI tend to be located in the outer regions of the cluster and to be brighter. Early-type dwarfs with HI may be undergoing morphological transition due to cluster environmental effects.
We have started a study of luminosity functions of Fossil Group candidates in order to characterize the faint-end of their galaxy distribution. Here we report on results of nine of them from SDSS photometry.
We investigate the young (proto)stellar population in NGC 2023 and the L 1630 molecular cloud bordering the HII region IC 434, using Spitzer IRAC and MIPS archive data, JCMT SCUBA imaging and spectroscopy as well as targeted BIMA observations of one of the Class 0 protostars, NGC 2023 MM1. We have performed photometry of all IRAC and MIPS images, and used color-color diagrams to identify and classify all young stars seen within a 22'x26' field along the boundary between IC 434 and L 1630. For some stars, which have sufficient optical, IR, and/or sub-millimeter data we have also used the online SED fitting tool for a large 2D archive of axisymmetric radiative transfer models to perform more detailed modeling of the observed SEDs. We identify 5 sub-millimeter cores in our 850 and 450 micron SCUBA images, two of which have embedded class 0 or I protostars. Observations with BIMA are used to refine the position and characteristics of the Class 0 source NGC 2023 MM 1. These observations show that it is embedded in a very cold cloud core, which is strongly enhanced in NH2D. We find that HD 37903 is the most massive member of a cluster with 20 -- 30 PMS stars. We also find smaller groups of PMS stars formed from the Horsehead nebula and another elephant trunk structure to the north of the Horsehead. We refine the spectral classification of HD 37903 to B2 Ve. Our study shows that the expansion of the IC 434 HII region has triggered star formation in some of the dense elephant trunk structures and compressed gas inside the L 1630 molecular cloud. This pre-shock region is seen as a sub-millimeter ridge in which stars have already formed. The cluster associated with NGC 2023 is very young, and has a large fraction of Class I sources.
Based on recent findings of a formation mechanism of substructure in tidal
tails by Kuepper, Macleod & Heggie (2008) we investigate a more comprehensive
set of N-body models of star clusters on orbits about a Milky-Way-like
potential. We find that the predicted epicyclic overdensities arise in any
tidal tail no matter which orbit the cluster follows as long as the cluster
lives long enough for the overdensities to build up.
The distance of the overdensities along the tidal tail from the cluster
centre depends for circular orbits only on the mass of the cluster and the
strength of the tidal field, and therefore decreases monotonically with time,
while for eccentric orbits the orbital motion influences the distance, causing
a periodic compression and stretching of the tails and making the distance
oscillate with time. We provide an approximation for estimating the distance of
the overdensities in this case.
We describe an additional type of overdensity which arises in extended tidal
tails of clusters on eccentric orbits, when the acceleration of the tidal field
on the stellar stream is no longer homogeneous. Moreover, we conclude that a
pericentre passage or a disk shock is not the direct origin of an overdensity
within a tidal tail. Escape due to such tidal perturbations does not take place
immediately after the perturbation but is rather delayed and spread over the
orbit of the cluster. All observable overdensities are therefore of the
mentioned two types. In particular, we note that substructured tidal tails do
not imply the existence of dark-matter sub-structures in the haloes of
galaxies.
We have measured the speed of both pressure waves and shear waves as a function of depth between 80 and 500 m depth in South Pole ice with better than 1% precision. The measurements were made using the South Pole Acoustic Test Setup ({SPATS}), an array of transmitters and sensors deployed in the ice at South Pole Station in order to measure the acoustic properties relevant to acoustic detection of astrophysical neutrinos. The transmitters and sensors use piezoceramics operating at $\sim$5-25 kHz. Between 200 m and 500 m depth, the measured profile is consistent with zero variation of the sound speed with depth, resulting in zero refraction, for both pressure and shear waves. We also performed a complementary study featuring an explosive signal propagating from 50 to 2250 m depth, from which we determined a value for the pressure wave speed consistent with that determined with the sensors operating at shallower depths and higher frequencies. These results have encouraging implications for neutrino astronomy: The negligible refraction of acoustic waves deeper than 200 m indicates that good neutrino direction and energy reconstruction, as well as separation from background events, could be achieved.
We have undertaken a project to investigate the host galaxies and environments of a sample of quasars at z~4. In this paper, we describe deep near-infrared imaging of 34 targets using the Magellan I and Gemini North telescopes. We discuss in detail special challenges of distortion and nonlinearity that must be addressed when performing PSF subtraction with data from these telescopes and their IR cameras, especially in very good seeing. We derive black hole masses from emission-line spectroscopy, and we calculate accretion rates from our K_s-band photometry, which directly samples the rest-frame B for these objects. We introduce a new isophotal diameter technique for estimating host galaxy luminosities. We report the detection of four host galaxies on our deepest, sharpest images, and present upper limits for the others. We find that if host galaxies passively evolve such that they brighten by 2 magnitudes or more in the rest-frame B band between the present and z=4, then high-z hosts are less massive at a given black hole mass than are their low-z counterparts. We argue that the most massive hosts plateau at <~10L*. We estimate the importance of selection effects on this survey and the subsequent limitations of our conclusions. These results are in broad agreement with recent semi-analytical models for the formation of luminous quasars and their host spheroids by mergers of gas-rich galaxies, with significant dissipation, and self-regulation of black hole growth and star-formation by the burst of merger-induced quasar activity.
In this Paper we report on radio (VLA and ATCA) and X-ray (RXTE, Chandra and Swift) observations of the outburst decay of the transient black hole candidate H1743-322 in early 2008. We find that the X-ray light curve followed an exponential decay, leveling off towards its quiescent level. The exponential decay timescale is ~4 days and the quiescent flux corresponds to a luminosity of 3x10^32 (d/7.5 kpc)^2 erg/s. This together with the relation between quiescent X-ray luminosity and orbital period reported in the literature suggests that H1743-322 has an orbital period longer than ~10 hours. Both the radio and X-ray light curve show evidence for flares. The radio - X-ray correlation can be well described by a power-law with index ~0.18. This is much lower than the index of 0.6-0.7 found for the decay of several black hole transients before. The radio spectral index measured during one of the radio flares while the source is in the low-hard state, is -0.5+-0.15, which indicates that the radio emission is optically thin. This is unlike what has been found before in black hole sources in the low-hard state. We attribute the radio flares and the low index for the radio - X-ray correlation to the presence of shocks downstream the jet flow, triggered by ejection events earlier in the outburst. We find no evidence for a change in X-ray power law spectral index during the decay, although the relatively high extinction of N_H =2.3x10^22 cm^-2 limits the detected number of soft photons and thus the accuracy of the spectral fits.
Calibrated data for 143 flat-spectrum extragalactic radio sources are presented at a wavelength of 850 microns covering a five-year period from April 2000. The data, obtained at the James Clerk Maxwell Telescope using the SCUBA camera in pointing mode, were analysed using an automated pipeline process based on the Observatory Reduction and Acquisition Control - Data Reduction (ORAC-DR) system. This paper describes the techniques used to analyse and calibrate the data, and presents the database of results along with a representative sample of the better-sampled lightcurves. A re-analysis of previously published data from 1997 to 2000 is also presented. The combined catalogue, comprising 10493 flux density measurements, provides a unique and valuable resource for studies of extragalactic radio sources.
Beryllium stellar abundances were suggested to be a good tracer of time in the early Galaxy. In an investigation of its use as a cosmochronometer, using a large sample of local halo and thick-disk dwarfs, evidence was found that in a log(Be/H) vs. [alpha/Fe] diagram the halo stars separate into two components. One is consistent with predictions of evolutionary models while the other is chemically indistinguishable from the thick-disk stars. This is interpreted as a difference in the star formation history of the two components and suggests that the local halo is not a single uniform population where a clear age-metallicity relation can be defined.
We present a model of weak scale Dark Matter (DM) where the thermal DM density is set by the lepton asymmetry due to the presence of higher dimension lepton violating operators. In these models there is generically a separation between the annihilation cross-section responsible for the relic abundance (through lepton violating operators) and the annihilation cross-section that is relevant for the indirect detection of DM (through lepton preserving operators). Due to this separation, there is a perceived boost in the annihilation cross-section in the galaxy today relative to that derived for canonical thermal freeze-out. This results in a natural explanation for the observed cosmic ray electron and positron excesses, without resorting to a Sommerfeld enhancement. Generating the indirect signals also sets the magnitude of the direct detection cross-section which implies a signal for the next generation of experiments. More generically these models motivate continued searches for DM with apparently non-thermal annihilation cross-sections. The DM may also play a role in radiatively generating Majorana neutrino masses.
We show that it is possible to obtain a picture of equilibrium thermodynamics on the apparent horizon in the expanding cosmological background for a wide class of modified gravity theories with the Lagrangian density $f(R, \phi, X)$, where $R$ is the Ricci scalar and $X=-(\nabla \phi)^2/2$ is the kinetic energy of a scalar field $\phi$. This comes from a suitable definition of an energy momentum tensor of the ``dark'' component that respects to a local energy conservation. In this framework the horizon entropy $S$ corresponding to equilibrium thermodynamics is proportional to the horizon area $A$ with a constant coefficient, as in the Einstein gravity. For a flat cosmological background with a decreasing Hubble parameter, $S$ globally increases with time, as it happens for viable $f(R)$ inflation and dark energy models. We also show that the equilibrium description in terms of the horizon entropy $S$ is convenient because it takes into account the contribution of both the horizon entropy $\hat{S}$ in non-equilibrium thermodynamics and an entropy production term.
Using the dynamical system approach, properties of cosmological models based on the Horava-Lifshitz gravity are systematically studied. In particular, the cosmological phase space of the Horava-Lifshitz model is characterized. The analysis allows to compare some key physical consequences of the imposition (or not) of detailed balance. A result of the investigation is that in the detailed balance case one of the attractors in the theory corresponds to an oscillatory behavior. Such oscillations can be associated to a bouncing universe, as previously described by Brandenberger, and will prevent a possible evolution towards a de Sitter universe. Other results obtained show that the cosmological models generated by Horava-Lifshitz gravity without the detailed balance assumption have indeed the potential to describe the transition between the Friedmann and the dark energy eras. The whole analysis leads to the plausible conclusion that a cosmology compatible with the present observations of the universe can be achieved only if the detailed balance condition is broken.
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The Dirac-Born-Infeld (DBI) action from string theory provides several new classes of dark energy behavior beyond quintessence due to its relativistic kinematics. We constrain parameters of natural potentials and brane tensions with cosmological observations as well as showing how to design these functions for a desired expansion history. We enlarge the attractor solutions, including new ways of obtaining cosmological constant behavior, to the case of generalized DBI theory with multiple branes. An interesting novel signature of DBI attractors is that the sound speed is driven to zero, unlike for quintessence where it is the speed of light.
While galaxies move through the intracluster medium of their host cluster, they experience a ram pressure which removes at least a significant part of their interstellar medium. This ram pressure stripping appears to be especially important for spiral galaxies: this scenario is a good candidate to explain the differences observed between cluster spirals in the nearby universe and their field counterparts. Thus, ram pressure stripping of disk galaxies in clusters has been studied intensively during the last decade. I review advances made in this area, concentrating on theoretical work, but continuously comparing to observations.
We present a library of 139 near-IR spectra of cool asymptotic giant branch stars that will be useful for comparison with theoretical model atmosphere calculations and for modeling the integrated emission from intermediate-age stellar populations. The source list was selected from the `extremely red' region of the INT Photometric H Alpha Survey (IPHAS) colour-colour plane that is overwhelmingly dominated by very late-type stars. The spectral library also includes a large fraction of S-type and carbon stars. We present a number of spectral classification sequences highlighting the various molecular features identified and discuss a number of rare features with uncertain identifications in the literature. With its focus on particularly cool photospheres this catalogue serves as a companion to recent spectroscopic atlases of MK standards in the near-IR. Finally the relationship between IPHAS (r'-i') and (r'-H Alpha) colours and spectroscopically determined properties is discussed and a strong correlation between (r'-H Alpha) colour and the C/O abundance index for S-type and carbon stars is noted. This relation has the potential to separate O-rich, S-type and carbon stars in the Galaxy based on their photometry alone.
The mode of explosive burning in Type Ia SNe remains an outstanding problem. It is generally thought to begin as a subsonic deflagration, but this may transition into a supersonic detonation (the DDT). We argue that this transition leads to a breakout shock, which would provide the first unambiguous evidence that DDTs occur. Its main features are a hard X-ray flash (~20 keV) lasting ~0.01 s with a total radiated energy of ~10^{40} ergs, followed by a cooling tail. This creates a distinct feature in the visual light curve, which is separate from the nickel decay. This cooling tail has a maximum absolute visual magnitude of M_V = -9 to -10 at approximately 1 day, which depends most sensitively on the white dwarf radius at the time of the DDT. As the thermal diffusion wave moves in, the composition of these surface layers may be imprinted as spectral features, which would help to discern between SN Ia progenitor models. Since this feature should accompany every SNe Ia, future deep surveys (e.g., m=24) will see it out to a distance of approximately 80 Mpc, giving a maximum rate of ~60/yr. Archival data sets can also be used to study the early rise dictated by the shock heating (at about 20 days before maximum B-band light). A similar and slightly brighter event may also accompany core bounce during the accretion induced collapse to a neutron star, but with a lower occurrence rate.
Recent direct imaging discoveries suggest a new class of massive, distant planets around A stars. These widely separated giants have been interpreted as signs of planet formation driven by gravitational instability, but the viability of this mechanism is not clear cut. In this paper, we not only derive the local requirements for fragmentation and the initial fragment masses, but also we consider the fragment's subsequent growth and whether it can be terminated within the planetary mass regime. Finally, we place disks in the larger context of star formation and disk evolution models. In order for gravitational instability to produce planets we find that disks must be atypically cold in order to reduce the initial fragment mass, and have unusually low viscosity following fragmentation in order to limit continued growth through gaps. In addition, fragmentation must occur during a narrow window of disk evolution, after infall has mostly ceased, but while the disk is still sufficiently massive to undergo gravitational instability. Under more typical conditions, disk-born objects will likely grow up to an order of magnitude above the deuterium burning planetary mass limit. If planets are formed by gravitational instability, then they must be the low mass tail of the distribution of disk-born binaries. To validate this theory, on-going direct imaging surveys must find a greater abundance of brown dwarf and M-star companions to A-stars. Their absence would suggest planet formation by a different mechanism such as core accretion, which is consistent with the debris disks detected in these systems.
This paper presents a sample of "cold front" clusters selected from the Chandra archive. The clusters are selected based purely on the existence of surface brightness edges in their Chandra images which are modeled as density jumps. A combination of the derived density and temperature jumps across the fronts is used to select nine robust examples of cold front clusters: 1ES0657-558, Abell 1201, Abell 1758N, MS1455.0+2232, Abell 2069, Abell 2142, Abell 2163, RXJ1720.1+2638, and Abell 3667. This sample is the subject of an ongoing study aimed at relating cold fronts to cluster merger activity, and understanding how the merging environment affects the cluster constituents. Here, temperature maps are presented along with the Chandra X-ray images. A dichotomy is found in the sample in that there exists a subsample of cold front clusters which are clearly mergers based on their X-ray morphologies, and a second subsample which harbor cold fronts, but have surprisingly relaxed X-ray morphologies, and minimal evidence for merger activity at other wavelengths. For this second subsample, the existence of a cold front provides the sole evidence for merger activity at X-ray wavelengths. We discuss how cold fronts can provide additional information which may be used to constrain merger histories, and also the possibility of using cold fronts to distinguish major and minor mergers.
In the hot, dense plasma of solar and stellar interiors, the Coulomb interaction is screened by the surrounding plasma. Although the standard Salpeter approximation for static screening is widely accepted and used in stellar modeling, the question of dynamic screening has been revisited. In particular, Shaviv and Shaviv apply the techniques of molecular dynamics to the conditions in the solar core in order to numerically determine the dynamic screening effect. By directly calculating the motion of ions and electrons due to Coulomb interactions, they compute the effect of screening without the mean-field assumption inherent in the Salpeter approximation. Here we reproduce their numerical analysis of the screening energy in the plasma of the solar core and conclude that the effects of dynamic screening are relevant and should be included in the treatment of the plasma, especially in the computation of stellar nuclear reaction rates.
We present ultraviolet through far-infrared surface brightness profiles for the 75 galaxies in the Spitzer Infrared Nearby Galaxies Survey (SINGS). The imagery used to measure the profiles includes GALEX UV data, optical images from KPNO, CTIO and SDSS, near-IR data from 2MASS, and mid- and far-infrared images from Spitzer. Along with the radial profiles, we also provide multi-wavelength asymptotic magnitudes and several non-parametric indicators of galaxy morphology: the concentration index (C_42), the asymmetry (A), the Gini coefficient (G) and the normalized second-order moment of the brightest 20% of the galaxy's flux (M_20). Our radial profiles show a wide range of morphologies and multiple components (bulges, exponential disks, inner and outer disk truncations, etc.) that vary not only from galaxy to galaxy but also with wavelength for a given object. In the optical and near-IR, the SINGS galaxies occupy the same regions in the C_42-A-G-M_20 parameter space as other normal galaxies in previous studies. However, they appear much less centrally concentrated, more asymmetric and with larger values of G when viewed in the UV (due to star-forming clumps scattered across the disk) and in the mid-IR (due to the emission of Polycyclic Aromatic Hydrocarbons at 8.0 microns and very hot dust at 24 microns).
Cosmologists will soon be in a unique position. Observational noise will gradually be replaced by cosmic variance as the dominant source of uncertainty in an increasing number of observations. We reflect on the ramifications for the discovery and verification of new models. If there are features in the full data set that call for a new model, there will be no subsequent observations to test that model's predictions. We show how the gradual release of data can mitigate this difficulty, allowing anomalies to be identified, and new models to be proposed and tested. We advocate that observers plan for the frugal release of data from future cosmic variance limited observations.
We present SHARC-II 350um imaging of twelve 24um-bright (F_24um > 0.8 mJy) Dust-Obscured Galaxies (DOGs) and CARMA 1mm imaging of a subset of 2 DOGs, all selected from the Bootes field of the NOAO Deep Wide-Field Survey. Detections of 4 DOGs at 350um imply IR luminosities which are consistent within a factor of 2 of expectations based on a warm dust spectral energy distribution (SED) scaled to the observed 24um flux density. The 350um upper limits for the 8 non-detected DOGs are consistent with both Mrk231 and M82 (warm dust SEDs), but exclude cold dust (Arp220) SEDs. The two DOGs targeted at 1mm were not detected in our CARMA observations, placing strong constraints on the dust temperature: T_dust > 35-60 K. Assuming these dust properties apply to the entire sample, we find dust masses of ~3x10^8 M_sun. In comparison to other dusty z ~ 2 galaxy populations such as sub-millimeter galaxies (SMGs) and other Spitzer-selected high-redshift sources, this sample of DOGs has higher IR luminosities (2x10^13 L_sun vs. 6x10^12 L_sun for the other galaxy populations), warmer dust temperatures (>35-60 K vs. ~30 K), and lower inferred dust masses (3x10^8 M_sun vs. 3x10^9 M_sun). Herschel and SCUBA-2 surveys should be able to detect hundreds of these power-law dominated DOGs. We use HST and Spitzer/IRAC data to estimate stellar masses of these sources and find that the stellar to gas mass ratio may be higher in our 24um-bright sample of DOGs than in SMGs and other Spitzer-selected sources. Although larger sample sizes are needed to provide a definitive conclusion, the data are consistent with an evolutionary trend in which the formation of massive galaxies at z~2 involves a sub-millimeter bright, cold-dust and star-formation dominated phase followed by a 24um-bright, warm-dust and AGN-dominated phase.
Planets are built from planetesimals: solids larger than a kilometer which grow by colliding pairwise. Planetesimals themselves are unlikely to form by two-body collisions; sub-km objects have gravitational fields individually too weak, and electrostatic attraction is too feeble for growth beyond a few cm. We review the possibility that planetesimals form when self-gravity brings together vast ensembles of small particles. Even when self-gravity is weak, aerodynamic processes can accumulate solids relative to gas, paving the way for gravitational collapse. Particles pile up as they drift radially inward. Gas turbulence stirs particles, but can also seed collapse by clumping them. While the feedback of solids on gas triggers vertical shear instabilities that obstruct self-gravity, this same feedback triggers streaming instabilities that strongly concentrate particles. Numerical simulations find that solids 10-100 cm in size gravitationally collapse in turbulent disks. We outline areas for progress, including the possibility that still smaller objects self-gravitate.
We present a detailed analysis of the radial distribution of dust properties in the SINGS sample, performed on a set of UV, IR and HI surface brightness profiles, combined with published molecular gas profiles and metallicity gradients. The internal extinction, derived from the TIR-to-FUV luminosity ratio, decreases with radius, and is larger in Sb-Sbc galaxies. The TIR-to-FUV ratio correlates with the UV spectral slope beta, following a sequence shifted to redder UV colors with respect to that of starbursts. The star formation history (SFH) is identified as the main driver of this departure. We have also derived radial profiles of the total dust mass surface density, the fraction of the dust mass contributed by PAHs, the fraction of the dust mass heated by very intense starlight and the intensity of the radiation field heating the grains. The dust profiles are exponential, their radial scale-length being constant from Sb to Sd galaxies (only ~10% larger than the stellar scale-length). Many S0/a-Sab galaxies have central depressions in their dust radial distributions. The PAH abundance increases with metallicity for 12+\log(O/H)<9, and at larger metallicities the trend flattens and even reverses, with the SFH being a plausible underlying driver for this behavior. The dust-to-gas ratio is also well correlated with metallicity and therefore decreases with galactocentric radius.
Current high resolution observations of galaxy clusters reveal a dynamical intracluster medium (ICM). The wealth of structures includes signatures of interactions between active galactic nuclei (AGN) and the ICM, such as cavities and shocks, as well as signatures of bulk motions, e.g. cold fronts. Aiming at understanding the physics of the ICM, we study individual clusters by both, deep high resolution observations and numerical simulations which include processes suspected to be at work, and aim at reproducing the observed properties. By comparing observations and simulations in detail, we gain deeper insights into cluster properties and processes. Here we present two examples of our approach: the large-scale shock in the Hydra A cluster, and sloshing cold fronts.
The recent discoveries of massive planets on ultra-wide orbits orbiting HR
8799 (Marois et al. 2008) and Fomalhaut (Kalas et al. 2008) present a new
challenge for planet formation theorists. Our goal is to figure out which of
three giant planet formation mechanisms--core accretion (with or without
migration), scattering from the inner disk, or gravitational instability--could
be responsible for Fomalhaut b, HR 8799 b, c and d, and similar planets
discovered in the future. This paper presents the results of numerical
experiments comparing the long-period planet formation efficiency of each
possible mechanism in model A star, G star and M star disks.
First, a simple core accretion simulation shows that planet cores forming
beyond 35 AU cannot reach critical mass, even under the most favorable
conditions (A star with a massive disk and low velocity-dispersion
planetesimals) we can construct. Second, a set of N-body simulations
demonstrates that planet-planet scattering does not create stable, wide-orbit
systems such as HR 8799. Finally, a linear stability analysis verifies previous
work showing that global spiral instabilities naturally arise in high-mass
disks. We conclude that massive gas giants on stable orbits with semimajor axes
greater than 35 AU form by gravitational instability in the disk. We recommend
that observers examine the planet detection rate as a function of stellar age,
controlling for planet dimming with time. If planet detection rate is found to
be independent of stellar age, it would confirm our prediction that
gravitational instability is the dominant mode of producing detectable planets
on wide orbits.
We construct updated solar models with different sets of solar abundances, including the most recent determinations by Asplund et al. (2009). The latter work predicts a slightly larger solar metallicity compared to previous measurements by the same authors but significantly lower than the recommended value from a decade ago. The new solar models incorporate an updated equation of state and new determinations of nuclear cross-sections important for calculations of solar neutrino fluxes. We compare the results of our models with determinations of the solar structure inferred through helioseismology measurements. The model that uses the most recent solar abundance determinations predicts the base of the solar convective envelope to be located at $R_{\rm CZ}= 0.724{\rm R_\odot}$ and a surface helium mass fraction of $Y_{\rm surf}=0.231$. These results are still in conflict with helioseismology data ($R_{\rm CZ}= 0.713\pm0.001{\rm R_\odot}$ and $Y_{\rm surf}=0.2485\pm0.0035$) but the disagreement is less severe than with previous low-metallicity solar compositions. We find the improved input physics in the models has minor effects on the solar model structure and we confirm that the model using high (older) metallicity determinations gives consistent results with helioseismology. Using the new solar abundances, we calculate the magnitude by which radiative opacities should be modified in order to restore agreement with helioseismology. We also present the solar neutrino fluxes predicted by the new models.
The mechanism and the region of generation of variable continuum emission are poorly understood for radio-loud AGN because of a complexity of the nuclear region. High-resolution radio VLBI (very long baseline interferometry) observations allow zooming into a subparsec-scale region of the jet in the radio-loud galaxy 3C 390.3. We combined the radio VLBI and the optical data covering the time period of 14 years to look for a link between optical flares and parsec-scale jet. We identify two stationary and nine moving radio features in the innermost subparsec-scale region of the jet. We found a significant correlation (at a confidence level of >99.99 %) between the ejected jet components and optical continuum flares. The epochs at which the moving knots pass through the location of a stationary radio feature and the optical light curve reaches the maximum are correlated. The radio events follow the maxima of optical flares with the mean time delay of 0.10 years. This correlation can be understood if the variable optical continuum emission is generated in the innermost part of the jet. A possible mechanism of the energy release is the ejection of knots of high-energy electrons that are accelerated in the jet flow and generate flares of synchrotron continuum emission in the wide range of frequencies from radio to X-ray bands. In this scenario, the beamed optical continuum emission from the jet and counterjet ionizes a gas in a subrelativistic outflow surrounding the jet, which results in a formation of two outflowing conical regions with broad emission lines (in addition to the conventional broad line region around the central nucleus).
The origin of the observed dark energy could be explained entirely within the standard model, with no new fields required. We show how the low-energy sector of the chiral QCD Lagrangian, once embedded in a nontrivial spacetime, gives rise to a cosmological vacuum energy density which can be can be presented entirely in terms of QCD parameters and the Hubble constant $H$ as $\rho_\Lambda \simeq H \cdot m_q\la\bar{q}q\ra /m_{\eta'} \sim (4.3\cdot 10^{-3} \text{eV})^4$. In this work we focus on the dynamics of the ghost fields that are essential ingredients of the aforementioned Lagrangian. In particular, we argue that the Veneziano ghost, being unphysical in the usual Minkowski QFT, becomes a physical degree of freedom if the universe is expanding. As an immediate consequence, all relevant effects are naturally very small as they are proportional to the rate of expansion $H/ \Lqcd \sim 10^{-41}$. The co-existence of these two drastically different scales ($\Lqcd \sim 100 $ MeV and $H \sim 10^{-33}$ eV) does not stem from a superimposed supersymmetry or any other extra symmetry, but it is a direct consequence of the auxiliary conditions on the physical Hilbert space (similar to the Gupta-Bleuler condition in QED) that are necessary to keep the theory unitary. The exact cancellation taking place in Minkowski space due to this auxiliary condition is slightly violated when the system is upgraded to an expanding background. Nevertheless, this "tiny" effect is in fact the driving force accelerating the universe today. We also derive the time dependent equation of state $w(t)$ for the dark energy component which tracks the dynamics of the Veneziano ghost in a FLRW universe.
We have obtained a full suite of Spitzer observations to characterize the debris disk around HR 8799 and to explore how its properties are related to the recently discovered set of three massive planets orbiting the star. We distinguish three components to the debris system: (1) warm dust (T ~150 K) orbiting within the innermost planet; (2) a broad zone of cold dust (T ~45 K) with a sharp inner edge, orbiting just outside the outermost planet and presumably sculpted by it; and (3) a dramatic halo of small grains originating in the cold dust component. The high level of dynamical activity implied by this halo may arise due to enhanced gravitational stirring by the massive planets. The relatively young age of HR 8799 places it in an important early stage of development and may provide some help in understanding the interaction of planets and planetary debris, an important process in the evolution of our own solar system.
We present full evolutionary calculations appropriate for the study of hot hydrogen-deficent DO white dwarfs, PG 1159 stars, and DB white dwarfs. White dwarf sequences are computed for a wide range of stellar masses and helium envelopes on the basis of a complete treatment of the evolutionary history of progenitors stars, including the core hydrogen and helium burning phases, the thermally-pulsing AGB phase, and the born-again episode that is responsible for the hydrogen deficiency. We also provide colors and magnitudes for the new sequences for $T_{\rm eff} < 40 000$ K, where the NLTE effects are not dominant. These new calculations provide an homogeneous set of evolutionary tracks appropriate for mass and age determinations for both PG 1159 stars and DO white dwarfs. The calculations are extended down to an effective temperature of 7 000 K. We applied these new tracks to redetermine stellar masses and ages of all known DO white dwarfs with spectroscopically-determined effective temperatures and gravities, and compare them with previous results. We also compare for the first time consistent mass determinations for both DO and PG 1159 stars, and find a considerably higher mean mass for the DO white dwarfs. We discuss as well the chemical profile expected in the envelope of variable DB white dwarfs from the consideration of the evolutionary history of progenitor stars. Finally, we present tentative evidence for a different evolutionary channel, other than that involving the PG 1159 stars, for the formation of hot, hydrogen-deficient white dwarfs.
We discuss the extent to which photometric measurements alone can be used to identify Type Ia supernovae (SNIa) and to determine redshift and other parameters of interest for cosmological studies. We fit the light curve data of the type expected from a survey such as the one planned with Large Synoptic Survey Telescope (LSST) and also to remove the contamination from the core-collapse supernovae to SNIa samples. We generate 1000 SNIa mock flux data for each of the LSST filters based on existing design parameters, then use a Markov Chain Monte-Carlo (MCMC) analysis to fit for the redshift, apparent magnitude, stretch factor and the phase of the SNIa. We find that the model fitting works adequately well when the true SNe redshift is below 0.5, while at $z < 0.2$ the accuracy of the photometric data is almost comparable with spectroscopic measurements of the same sample. We discuss the contamination of Type Ib/c (SNIb/c) and Type II supernova (SNII) on the SNIa data set. We find it is easy to distinguish the SNII through the large $\chi^2$ mismatch when fitting to photometric data with Ia light curves. This is not the case for SNIb/c. We implement a statistical method based on the Bayesian estimation in order to statistically reduce the contamination from SNIb/c for cosmological parameter measurements from the whole SNe sample. The proposed statistical method also evaluate the fraction of the SNIa in the total SNe data set, which provides a valuable guide to establish the degree of contamination.
There has not been a comprehensive framework for comparing spectral data from different planets.Such a framework is needed for the study of extrasolar planets and objects within the solar system. We have undertaken observations to compile a library of planet spectra for all planets, some moons, and some dwarf planets in the solar system to study their general spectroscopic and photometric natures. During May and November of 2008, we acquired spectra for the planets using TRISPEC, which is capable of simultaneous three-band spectroscopy in a wide wavelength range of 0.45 - 2.5 microns with low resolving power (lambda-over-Delta-lambda is 140 - 360). Patterns emerge from comparing the spectra. Analyzing their general spectroscopic and photometric natures, we show that it is possible to distinguish between gas planets, soil planets and ice planets. These methods can be applied to extrasolar observations using low resolution spectrography or broad-band filters. The present planet spectral library is the first library to contain observational spectra for all of the solar system planets, based on simultaneous observations in visible and near infrared wavelengths. This library will be a useful reference for analyzing extrasolar planet spectra, and for calibrating planetary data sets.
A pulsar beam passing close to a black hole can provide a probe of very strong gravitational fields even if the pulsar itself is not in a strong field region. In the case that the spin of the hole can be ignored, we have previously shown that all strong field effects on the beam can be understood in terms of two "universal" functions, $F(\phi_{\rm in})$ and $T(\phi_{\rm in})$ of the angle of beam emission $\phi_{\rm in}$; these functions are universal in that they depend only on a single parameter, the pulsar/black hole distance from which the beam is emitted. Here we apply this formalism to general pulsar-hole-observer geometries, with arbitrary alignment of the pulsar spin axis and arbitrary pulsar beam direction and angular width. We show that the analysis of the observational problem has two distinct elements: (i) the computation of the location and trajectory of an observer-dependent "keyhole" direction of emission in which a signal can be received by the observer; (ii) the determination of an annulus that represents the set of directions containing beam energy. Examples of each are given along with an example of a specific observational scenario.
Studying the atomic gas (HI) properties of the most isolated galaxies is essential to quantify the effect that the environment exerts on this sensitive component of the interstellar medium. We observed and compiled HI data for a well defined sample of ~ 800 galaxies in the Catalog of Isolated Galaxies, as part of the AMIGA project (Analysis of the ISM in Isolated GAlaxies, this http URL), which enlarges considerably previous samples used to quantify the HI deficiency in galaxies located in denser environments. By studying the shape of 182 HI profiles, we revisited the usually accepted result that, independently of the environment, more than half of the galaxies present a perturbed HI disk. In isolated galaxies this would certainly be a striking result if these are supposed to be the most relaxed systems, and has implications in the relaxation time scales of HI disks and the nature of the most frequent perturbing mechanisms in galaxies. Our sample likely exhibits the lowest HI asymmetry level in the local Universe. We found that other field samples present an excess of ~ 20% more asymmetric HI profiles than that in CIG. Still a small percentage of galaxies in our sample present large asymmetries. Follow-up high resolution VLA maps give insight into the origin of such asymmetries.
The lower limit for the mass of white dwarfs (WDs) with C-O core is commonly assumed to be roughly 0.5 Msun. As a consequence, WDs of lower masses are usually identified as He-core remnants. However, when the initial mass of the progenitor star is in between 1.8 and 3 Msun, which corresponds to the so called red giant (RGB) phase transition, the mass of the H-exhausted core at the tip of the RGB is 0.3 < M_H/Msun < 0.5. Prompted by this well known result of stellar evolution theory, we investigate the possibility to form C-O WDs with mass M < 0.5 Msun. The pre-WD evolution of stars with initial mass of about 2.3 Msun, undergoing anomalous mass-loss episodes during the RGB phase and leading to the formation of WDs with He-rich or CO-rich cores have been computed. The cooling sequences of the resulting WDs are also described. We show that the minimum mass for a C-O WD is about 0.33 Msun, so that both He and C-O core WDs can exist in the mass range 0.33-0.5 Msun. The models computed for the present paper provide the theoretical tools to indentify the observational counterpart of very low mass remnants with a C-O core among those commonly ascribed to the He-core WD population in the progressively growing sample of observed WDs of low mass. Moreover, we show that the central He-burning phase of the stripped progeny of the 2.3 Msun star lasts longer and longer as the total mass decreases. In particular, the M= 0.33 Msun model takes about 800 Myr to exhausts its central helium, which is more than three time longer than the value of the standard 2.3 Msun star: it is, by far, the longest core-He burning lifetime. Finally, we find the occurrence of gravonuclear instabilities during the He-burning shell phase.
This talk tries to summarise where we are now, in the "nature and nurture" questions in galaxy formation and evolution, and briefly describe unsolved problems, and perspectives of progress.
Observations of CO molecules in the millimetrer domain at high redshift
(larger than 1), have provided interesting informations about star formation
efficiency, and its evolution with redshift. Due to the difficulty of the
detections, selection effects are important. The detection if often due to
gravitational amplification. Objects selected by their (far)infrared flux, are
in general associated to ULIRGS, mergers with starburst in the nuclear regions.
Quasars have been selected as powerful optical sources, and have been found to
be associated to starbursts, rich in gas. The gas fraction appears to be much
higher at redshift greater than 1.
Quasars allow to probe the end of the reionisation period, and the relation
between bulge and black hole mass. However these selection bias could have led
us to miss some gaseous galaxies, with low-efficiency of star formation, such
as the more quiescent objects selected by their BzK colors at z=1.5 or 2.
The Cosmic Microwave Background CMB originates from an early stage in the history of the universe. Observed low multipole contributions of CMB fluctuations have motivated the search for selection rules from the underlying topology of 3-space. Everitt (2004) has generated all homotopies for Platonic spherical 3-manifolds by face gluings. We transform the glue generators into isomorphic deck transformations. The deck transformations act on a spherical Platonic 3-manifold as prototile and tile the 3-sphere by its images. A complete set of orthonormal functions on the 3-sphere is spanned by the Wigner harmonic polynomials. For a tetrahedral, two cubic and three octahedral manifolds we construct algebraically linear combinations of Wigner polynomials, invariant under deck transformations and with domain the manifold. We prove boundary conditions on polyhedral faces from homotopy. By algebraic means we pass to a multipole expansion. Assuming random models of the CMB radiation, we derive multipole selection rules, depending on the point symmetry of the manifold.
Kinematical studies of low and high redshift galaxies enables to probe galaxy formation and evolution scenarios. Integral field spectroscopy is a powerful tool to study with accuracy nearby galaxies kinematics. Recent observations also gives a new 2D vision of high redshift galaxies kinematics. This work mostly relies on the kinematical sample of galaxies GHASP. This control sample, composed of 203 local spiral and irregular galaxies in low density environments observed with Fabry-Perot techniques in the Ha line (6563 A), is by now the largest sample of Fabry-Perot data. After a revue on Fabry-Perot interferometry and a presentation of new data reduction procedures, my implications on both 3D-NTT Fabry-Perot instrument and the wide field spectrograph project (WFSpec) for galaxy evolution study with the european ELT are developed. The second section is dedicated to GHASP data. This sample have been fully reduced and analysed using new methods. The kinematical analysis of 2D kinematical maps has been undertaken with the study of the dark matter distribution, the rotation curves shape, bar signatures and the ionized gas velocity dispersion. In a third section, this local reference sample is used as a zero point for high redshift galaxies kinematical studies. The GHASP sample is projected at high redshift (z=1.7) in order to disentangle evolution effects from distance biases in high redshift galaxies kinematical data observed with SINFONI, OSIRIS and GIRAFFE. The kinematical analysis of new SINFONI high redshift observations is also presented and high redshift data found in the literature are compared with GHASP projected sample, suggesting some evolution of the galaxy dynamical support within the ages.
We present time-resolved spectroscopy and photometry of SDSS J100658.40+233724.4, which we have discovered to be an eclipsing cataclysmic variable with an orbital period of 0.18591324 days (267.71507 min). The observed velocity amplitude of the secondary star is 276 +/- 7 km/s, which an irradiation correction reduces to 258 +/- 12 km/s. Doppler tomography of emission lines from the infrared calcium triplet supports this measurement. We have modelled the light curve using the LCURVE code and Markov Chain Monte Carlo simulations, finding a mass ratio of 0.51 +/- 0.08. From the velocity amplitude and the light curve analysis we find the mass of the white dwarf to be 0.78 +/- 0.12 Msun and the masses and radii of the secondary star to be 0.40 +/- 0.10 Msun and 0.466 +/- 0.036 Rsun, respectively. The secondary component is less dense than a normal main sequence star but its properties are in good agreement with the expected values for a CV of this orbital period. By modelling the spectral energy distribution of the system we find a distance of 676 +/- 40 pc and estimate a white dwarf effective temperature of 16500 +/- 2000 K.
In the present work, we perform time-series analysis on the latitude bins of the solar full disk (SFD) images of Nobeyama Radioheliograph (NoRH) at 17 GHz. The flux modulation method traces the passage of radio features over the solar disc and the autocorrelation analysis of the time-series data of SFD images (one per day) for the period 1999-2001 gives the rotation period as a function of latitude extending from 60 degree S to 60 degree N. The results show that the solar corona rotates less differentially than the photosphere and chromosphere, i.e., it has smaller gradient in the rotation rate.
In order to test the recently proposed classification of the radio/X-ray states of the X-ray binary Cyg X-3, we present an analysis of the radio data available for the system at much higher spatial resolutions than used for defining the states. The radio data set consists of archival VLBA data at 5 or 15 GHz and new e-EVN data at 5 GHz. We also present 5 GHz MERLIN observations of an outburst of Cyg X-3. In the X-ray regime we use quasi-simultaneous with radio, monitoring and pointed RXTE observations. We find that when the radio emission from both jet and core is globally considered, the behaviour of Cyg X-3 at milliarcsecond scales is consistent with that described at arcsecond scales. However, when the radio emission is disentangled in a core component and a jet component the situation changes. It becomes clear that in active states the radio emission from the jet is dominating that from the core. This shows that in these states the overall radio flux cannot be used as a direct tracer of the accretion state.
From recent high resolution observations obtained with the Swedish 1 m Solar Telescope in La Palma, we detect swaying motions of individual filament threads in the plane of the sky. The oscillatory character of these motions are comparable with oscillatory Doppler signals obtained from corresponding filament threads. Simultaneous recordings of motions in the line of sight and in the plane of the sky give information about the orientation of the oscillatory plane. These oscillations are interpreted in the context of the magnetohydrodynamic theory. Kink magnetohydrodynamic waves supported by the thread body are proposed as an explanation of the observed thread oscillations. On the basis of this interpretation and by means of seismological arguments, we give an estimation of the thread Alfv\'en speed and magnetic field strength by means of seismological arguments.
Since autumn 2008 a new L-band 7-Feed-Array receiver is used for an HI 21-cm
line survey performed with the 100-m Effelsberg telescope. The survey will
cover the whole northern hemisphere comprising both, the galactic and
extragalactic sky in parallel. Using state-of-the-art FPGA based digital Fast
Fourier Transform spectrometers, superior in dynamic range and temporal
resolution, allows to apply sophisticated radio frequency interferences (RFI)
mitigation schemes to the survey data.
The EBHIS data reduction software includes the RFI mitigation, gain-curve
correction, intensity calibration, stray-radiation correction, gridding, and
source detection. We discuss the severe degradation of radio astronomical HI
data by RFI signals and the gain in scientific yield when applying modern RFI
mitigation schemes. For this aim simulations of the galaxy distribution within
the local volume (z<0.07) with and without RFI degradation were performed.
These simulations, allow us to investigate potential biases and selection
effects introduced by the data reduction software and the applied source
parametrization methods.
Recent studies of the circumgalactic gaseous environment of the Milky Way
have concentrated on the distribution, chemical composition, and physical
properties of the most massive neutral gas clouds and the highly-ionized halo
absorbers. Relatively little effort has been put so far in exploring the
circumgalactic neutral and weakly ionized metal absorbers at low HI column
densities.
With our work we systematically study the distribution and physical
properties of neutral and ionised low-column density gas in the halo of the
Milky Way. We combine CaII and NaI absorption line measurements with HI 21-cm
emission line data. For some of the sight lines high-resolution radio synthesis
observations were performed allowing us to study small-scale structures that
cannot be resolved with single dish telescopes.
In total 177 lines of sight were observed, providing a large
absorption-selected data sample for the analysis of IVC and HVC gas in the
circumgalactic environment of the Milky Way. The study allows us to compare the
observed absorption column density distribution (CDD) of gas in the Milky Way
halo with the overall CDD of intervening absorbers towards quasars. The
sensitive absorption line analysis enables us to identify the neutral and
ionised gaseous structures at low column densities and small angular extent
that possibly remain unseen in large 21-cm all-sky surveys. If this gas cover a
significant portion of the sky, it possibly has a large influence on the
evolution of the Milky Way.
We aim to exploit the available INTEGRAL/SPI data to provide time-averaged
spectra of the brightest soft gamma-ray sources.
Employing a maximum-likelihood fit technique for our SPI data analysis, we
take as input to our source model the source catalog derived by Bouchet et al.
(2008) from a SPI all-sky study. We use the first four years of public SPI data
and extract spectra between 25 keV and 1 MeV for the 20 catalog sources
detected by Bouchet et al. at 200 - 600 keV with >= 2.5 sigma. In order to
verify our analysis, we also extract spectra for the same sources from the
corresponding INTEGRAL/ISGRI data. We fit adequate spectral models to the
energy range 25-1000 keV for SPI and 25-600 keV for ISGRI. We use our spectra
from the Crab (which is among the 20 sources studied here) and an empty
location in a crowded field to derive an estimation of the systematic errors.
The agreement between our SPI and ISGRI measurements is good if we normalise
them on the Crab spectrum. Our SPI flux measurements also agree well with those
by Bouchet et al. (2008). All 20 sources in our sample are detected
independently in the bands 25-100 keV and 100-200 keV. At 200-600 keV we detect
eight sources, at 600-1000 keV we detect two sources. Our spectra agree well
with the results from previous publications where available. For six of the 14
XRBs in our sample we find evidence for a hard powerlaw-component which becomes
dominant above the cutoff energy of the thermal Comptonization component. In
two of these cases, our study provides the first indication of such emission.
For the others, our results confirm previous studies. Our Crab spectrum (from
1.3 Ms exposure), shows a significant flux in all points and is well described
by a powerlaw with a break near 100 keV and spectral indices 2.11 and 2.20.
Little is known about the properties of extremely massive HI-galaxies. They
are extremely scarce and are - according to hierarchical structure formation -
only forming now (z < 1). The forthcoming deep HI SKA Pathfinders surveys will
uncover many more of them. This will lead to a better understanding of their
evolution and frequency, and the shape of the bright end of the HI mass
function.
The recently discovered galaxy HIZOA J0836-43 is one of the most HI-rich
galaxies (M(HI)=7.5 x 10^10Msun - and the nearest of its kind. As such it is an
ideal local probe of these elusive galaxies. Results from a detailed
investigation in the near- (IRSF) and far-infrared (Spitzer) of this local
HI-massive galaxy are presented. Unlike other giant HI galaxies, it is not of
low surface brightness. The galaxy is found to be a luminous starbursting
galaxy at an unexpected early stage of stellar mass building, more typical of
star-forming galaxies at higher redshift (z~0.7). With regard to its
environment, hence possible clues to its formation, the near infrared imaging
survey finds HIZOAJ0836-43 to lie in a region underdense in L* galaxies -
consistent with the observation that HI-massive galaxies are preferentially
found in low density regions - in the presence, however, of an uncommonly large
number of low stellar mass galaxies.
We have determined the CMB temperature, $T(z)$, at redshifts in the range 0.023-0.546, from multi-frequency measurements of the S-Z effect towards 13 clusters. We extract the parameter $\alpha$ in the redshift scaling $T(z)=T_{0}(1+z)^{1-\alpha}$, which contrasts the prediction of the standard model ($\alpha=0$) with that in non-adiabatic evolution conjectured in some alternative cosmological models. The statistical analysis is based on two main approaches: using ratios of the S-Z intensity change, $\Delta I$, thus taking advantage of the weak dependence of the ratios on IC gas properties, and using directly the $\Delta I$ measurements. In the former method dependence on the Thomson optical depth and gas temperature is only second order in these quantities. In the second method we marginalize over these quantities which appear to first order in the intensity change. The marginalization itself is done in two ways - by direct integrations, and by a Monte Carlo Markov Chain approach. Employing these different methods we obtain two sets of results that are consistent with $\alpha=0$, in agreement with the prediction of the standard model.
We present a new Suzaku observation of the obscured AGN in NGC 1365, revealing an unexpected excess of X-rays above 20 keV of at least a factor ~2 with respect to the extrapolation of the best-fitting 3-10 keV model. Additional Swift-BAT and Integral-IBIS observations show that the 20-100 keV is concentrated within ~1.5 arcmin from the center of the galaxy, and is not significantly variable on time scales from days to years. A comparison of this component with the 3-10 keV emission, which is characterized by a rapidly variable absorption, suggests a complex structure of the circumnuclear medium, consisting of at least two distinct components with rather different physical properties, one of which covering >80% of the source with a column density NH~3-4x10^24 cm^(-2). An alternative explanation is the presence of a double active nucleus in the center of NGC 1365.
Supernova remnants interacting with molecular clouds are potentially exciting systems in which to detect evidence of cosmic ray acceleration. Prominent gamma-ray emission is produced via the decay of neutral pions when cosmic rays encounter the nearby dense clouds. In many of the supernova remnants coincident with gamma-ray sources, the presence of OH(1720 MHz) masers is used to identify interaction with dense gas and to provide a kinematic distance to the system. In this paper we use statistical tests to demonstrate that there is a correlation between these masers and a class of GeV- to TeV-energy gamma-ray sources coincident with interacting remnants. For pion decay, the gamma-ray luminosity provides a direct estimate of the local cosmic ray density. We find the cosmic ray density is enhanced by one to two orders of magnitude over the local solar value, comparable to X-ray-induced ionization in these remnants. The inferred ionization rates are sufficient to explain non-equilibrium chemistry in the post-shock gas, where high columns of hydroxyl are observed.
The High-Altitude Water Cherenkov (HAWC) Experiment is a second-generation highsensitivity gamma-ray and cosmic-ray detector that builds on the experience and technology of the Milagro observatory. Like Milagro, HAWC utilizes the water Cherenkov technique to measure extensive air showers. Instead of a pond filled with water (as in Milagro) an array of closely packed water tanks is used. The event direction will be reconstructed using the times when the PMTs in each tank are triggered. Therefore, the timing calibration will be crucial for reaching an angular resolution as low as 0.25 degrees.We propose to use a laser calibration system, patterned after the calibration system in Milagro. Like Milagro, the HAWC optical calibration system will use ~1 ns laser light pulses. Unlike Milagro, the PMTs are optically isolated and require their own optical fiber calibration. For HAWC the laser light pulses will be directed through a series of optical fan-outs and fibers to illuminate the PMTs in approximately one half of the tanks on any given pulse. Time slewing corrections will be made using neutraldensity filters to control the light intensity over 4 orders of magnitude. This system is envisioned to run continuously at a low rate and will be controlled remotely. In this paper, we present the design of the calibration system and first measurements of its performance.
The theoretical prediction of micro- and macroturbulence (xi_mic and xi_mac) as a function of stellar parameters can be useful for spectroscopic work based on 1D model atmospheres in cases where an empirical determination of xi_mic is impossible due to a lack of suitable lines and/or macroturbulence and rotational line broadening are difficult to separate. In an effort to exploit the CIFIST 3D model atmosphere grid for deriving the theoretical dependence of xi_mic and xi_mac on effective temperature, gravity, and metallicity, we discuss different methods to derive xi_mic from the numerical simulations, and report first results for the Sun and Procyon. In both cases the preliminary analysis indicates that the microturbulence found in the simulations is significantly lower than in the real stellar atmospheres.
We investigate mode coupling in a two dimensional compressible disc with radial stratification and differential rotation. We employ the global radial scaling of linear perturbations and study the linear modes in the local shearing sheet approximation. We employ a three-mode formalism and study the vorticity (W), entropy (S) and compressional (P) modes and their coupling properties. The system exhibits asymmetric three-mode coupling: these include mutual coupling of S and P-modes, S and W-modes, and asymmetric coupling between the W and P-modes. P-mode perturbations are able to generate potential vorticity through indirect three-mode coupling. This process indicates that compressional perturbations can lead to the development of vortical structures and influence the dynamics of radially stratified hydrodynamic accretion and protoplanetary discs.
Coronal holes are the darkest and least active regions of the Sun, as observed both on the solar disk and above the solar limb. Coronal holes are associated with rapidly expanding open magnetic fields and the acceleration of the high-speed solar wind. This paper reviews measurements of the plasma properties in coronal holes and how these measurements are used to reveal details about the physical processes that heat the solar corona and accelerate the solar wind. It is still unknown to what extent the solar wind is fed by flux tubes that remain open (and are energized by footpoint-driven wave-like fluctuations), and to what extent much of the mass and energy is input intermittently from closed loops into the open-field regions. Evidence for both paradigms is summarized in this paper. Special emphasis is also given to spectroscopic and coronagraphic measurements that allow the highly dynamic non-equilibrium evolution of the plasma to be followed as the asymptotic conditions in interplanetary space are established in the extended corona. For example, the importance of kinetic plasma physics and turbulence in coronal holes has been affirmed by surprising measurements from UVCS that heavy ions are heated to hundreds of times the temperatures of protons and electrons. These observations point to specific kinds of collisionless Alfven wave damping (i.e., ion cyclotron resonance), but complete models do not yet exist. Despite our incomplete knowledge of the complex multi-scale plasma physics, however, much progress has been made toward the goal of understanding the mechanisms responsible for producing the observed properties of coronal holes.
We reduced the observational logarithmic space densities in the vertical direction up to 8 kpc from the galactic plane, for stars with absolute magnitudes (5,6], (6,7] and [5,10] in the fields $#$0952+5245 and SA114, to a single exponential density law. One of three parameters in the quadratic expression of the density law corresponds to the local space density for stars with absolute magnitudes in question. There is no need of any definition for scaleheights or population types. We confirm with the arguments of non-discrete thin and thick discs for our Galaxy and propose a single structure up to several kiloparsecs from the galactic plane. The logarithmic space densities evaluated by this law for the ELAIS field fit to the observational ones. Whereas, there are considerable offsets for the logarithmic space densities produced by two sets of classical galactic model parameters from the observational ones, for the same field.
We perform a deep search for galaxies in the redshift range 6.5<z<7.5, to measure the evolution of the number density of luminous galaxies in this redshift range and derive useful constraints on the evolution of their Luminosity Function. We present here the first results of an ESO Large Program, that exploits the unique combination of area and sensitivity provided in the near-IR by the camera Hawk-I at the VLT. We have obtained two Hawk-I pointings on the GOODS South field for a total of 32 observing hours, covering ~90 arcmin2. The images reach Y=26.7 mags for the two fields. We have used public ACS images in the z band to select z-dropout galaxies with the colour criteria Z-Y>1, Y-J<1.5 and Y-K<2. The other public data in the UBVRIJHK bands are used to reject possible low redshift interlopers. The output has been compared with extensive Monte Carlo simulations to quantify the observational effects of our selection criteria as well as the effects of photometric errors. We detect 7 high quality candidates in the magnitude range Y=25.5-26.7. This interval samples the critical range for M* at z>6 (M_1500 ~- 19.5 to -21.5). After accounting for the expected incompleteness, we rule out at a 99% confidence level a Luminosity Function constant from z=6 to z=7, even including the effects of cosmic variance. For galaxies brighter than M_1500=-19.0 we derive a luminosity density rho_UV=1.5^{+2.0}_{-0.9} 10^25 erg/s/Hz/Mpc3, implying a decrease by a factor 3.5 from z=6 to z~6.8. On the basis of our findings, we make predictions for the surface densities expected in future surveys, either based on ULTRA-VISTA or on HST-WFC3, evaluating the best observational strategy to maximise their impact.
I use the Newtonian equation of hydrostatic equilibrium for an isotropic fluid sphere to generate exact anisotropic solutions of Einstein's equations. The input function is simply the density. An infinite number of regular solutions are constructed, some of which satisfy all the standard energy conditions. Two classes of these solutions generalize the Newtonian polytropes of index 0 and 1.
We propose that dark matter is dominantly comprised of atomic bound states. We build a simple model and map the parameter space that results in the early universe formation of hydrogen-like dark atoms. We find that atomic dark matter has interesting implications for cosmology as well as direct detection: Protohalo formation can be suppressed below $M_{proto} \sim 10^3 - 10^6 M_{\odot}$ for weak scale dark matter due to Ion-Radiation interactions in the dark sector. Moreover, weak-scale dark atoms can accommodate hyperfine splittings of order $100 \kev$, consistent with the inelastic dark matter interpretation of the DAMA data while naturally evading direct detection bounds.
A re-analysis of data from electron-pair production following 160 A GeV 207Pb bombardment of nuclear emulsions indicates the production and decay of neutral particles of significantly lower invariant mass and shorter lifetimes than previously claimed (J. Phys. G: Nucl. Part. Phys. 34 (2007) 129-138).
We consider the effect of non-standard neutrino interactions (NSI, for short) on the propagation of neutrinos through the supernova (SN) envelope within a three-neutrino framework and taking into account the presence of a neutrino background. We find that for given NSI parameters, with strength generically denoted by $\varepsilon_{ij}$, neutrino evolution exhibits a significant time dependence. For $|\varepsilon_{\tau\tau}|\gtrsim$ $10^{-3}$ the neutrino survival probability may become sensitive to the $\theta_{23}$ octant and the sign of $\varepsilon_{\tau\tau}$. In particular, if $\varepsilon_{\tau\tau}\gtrsim 10^{-2}$ an internal $I$-resonance may arise independently of the matter density. For typical values found in SN simulations this takes place in the same dense-neutrino region above the neutrinosphere where collective effects occur, in particular during the synchronization regime. This resonance may lead to an exchange of the neutrino fluxes entering the bipolar regime. The main consequences are (i) bipolar conversion taking place for normal neutrino mass hierarchy and (ii) a transformation of the flux of low-energy $\nu_e$, instead of the usual spectral swap.
Recently, a mechanism for relaxing a large cosmological constant (CC) has been proposed [arXiv:0902.2215], which transforms any initial vacuum energy density of arbitrary sign and magnitude into a harmless quantity without fine-tuning. The setup is implemented in the LXCDM framework, and it yields a reasonable cosmological background evolution similar to the LCDM model with a fine-tuned CC. In this work we analyse analytically the perturbations in this relaxation model, and we show that their evolution is also similar to the LCDM model, especially in the matter era. Some tracking properties of the vacuum energy are discussed, too.
Quantum Space Time may be characterized by a plethora of novel phenomena, such as Lorentz violations and non-trivial refractive indices, stochastic metric fluctuation effects leading to decoherence of quantum matter and non-commutativity of space-time coordinates. In string theory, which is one of the major approaches to quantum gravity, such coordinate non-commutativities arise naturally in many instances. In the talk I review one such instance, which arises in the modern context of D-brane defects in the background space time, over which string matter propagates. This serves as a prototype of space-time foam in this context. I chose this model, over many others, because it may actually have some unique features that can be falsified experimentally either by means of high-energy astrophysical observations or in some particle-interferometers, such as neutral meson factories. In particular, the model may explain the recent observations of the FERMI Gamma-Ray Telescope on delayed emission of 30 GeV photons from a distant Gamma-Ray-Burst 090510, in agreement with previous observations from the MAGIC and HESS Telescopes, but can also lead to falsifiable predictions for quantum foam effects in forthcoming upgrades of certain "particle interferometers", such as neutral meson factories.
In order to examine the gravitational waves emitted from the neutron stars in the tensor-vector-scalar (TeVeS) theory, we derive the perturbation equations for relativistic stars, where for simplicity we omit the perturbations of vector field. That is, we consider the perturbations of scalar and tensor fields. With this assumption, we find that the axial gravitational waves, which are corresponding to the oscillations of spacetime ($w$ modes), are independent from the perturbations of scalar field and the effects of scalar field can be mounted only via the background properties. Using two different equations of state, we calculate the complex eigenfrequencies of axial $w$ modes and find that the dependences of frequencies on the stellar compactness are almost independent from the adopted equation of state and the parameter in TeVeS. Additionally, these dependences of frequencies of axial $w$ modes in TeVeS is obviously different from those expected in the general relativity. Thus the direct observations of gravitational waves could reveal the gravitational theory in the strong-field regime.
We focus on Ho\v{r}ava-Lifshitz (HL) theory of gravity, and, in particular, on a spherically symmetric and asymptotically flat solution that is the analog of Schwarzschild black hole of General Relativity. In the weak-field and slow-motion approximation we analytically work out the secular precession of the longitude of the pericentre $\varpi$ of a test particle induced by this solution. Its analytical form is different from that of the general relativistic Einstein's pericentre precession. Then, we compare it to the latest determinations of the corrections $\Delta\dot\varpi$ to the standard Newtonian/Einsteinian planetary perihelion precessions recently estimated with the EPM and the INPOP ephemerides. It turns out that the inner planets of the solar system, taken singularly one at a time, allow to put upper bounds on the adimensional HL parameter psi_0 of the order of 10^-12-10^-11. The retrograde perihelion precession of Saturn, recently determined by processing large collections of Cassini ranging data by Pitjeva and Fienga et al., could, in principle, be explained by the HL model for psi_0 = 1-0.7 10^-18, which is in agreement with the constraints from the rocky planets taken singularly one at a time. Such a value is, instead, not able to account for the Pioneer anomalous acceleration for r>20 AU. The ratios of the determined corrections to the perihelion rates for some pairs of inner planets cannot be explained by the corresponding theoretically predicted ratios of the HL precessions at more than 1 sigma level.
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The orbits of binary stars precess as a result of general relativistic effects, forces arising from the asphericity of the stars, and forces from additional stars or planets in the system. For most binaries, the theoretical and observed precession rates are in agreement. One system, however -- DI Herculis -- has resisted explanation for 30 years. The observed precession rate is a factor of four slower than the theoretical rate, a disagreement that once was interpreted as evidence for a failure of general relativity. Among the contemporary explanations are the existence of a circumbinary planet and a large tilt of the stellar spin axes with respect to the orbit. Here we report that both stars of DI Herculis rotate with their spin axes nearly perpendicular to the orbital axis (contrary to the usual assumption for close binary stars). The rotationally induced stellar oblateness causes precession in the direction opposite to that of relativistic precession, thereby reconciling the theoretical and observed rates.
We investigate the relationship between the mass of a globular cluster core and the sizes of its various stellar populations in a sample of 56 globular clusters. The number of core red giant branch stars is found to scale sub-linearly with core mass at the 3-$\sigma$ confidence level, whereas the relation is linear to within one standard deviation for main-sequence turn-off and sub-giant branch stars. We interpret our results as evidence for a surplus of red giant branch stars in the least massive cluster cores which is not seen for main-sequence turn-off and sub-giant branch stars. We explore various possibilities for the source of this discrepancy, discussing our results primarily in terms of the interplay between the cluster dynamics and stellar evolution.
Vector perturbations sourced by topological defects can generate rotations in the lensing of background galaxies. This is a potential smoking gun for the existence of defects since rotation generates a curl-like component in the weak lensing signal which is not generated by standard density perturbations at linear order. This rotation signal is calculated as generated by cosmic strings. Future large scale weak lensing surveys should be able to detect this signal even for string tensions an order of magnitude lower than current constraints.
We have completed a pilot survey imaging 15 SDSS selected void galaxies in HI in local (d=50 to 100 Mpc) voids. This small sample makes up a surprisingly interesting collection of galaxies, consisting of galaxies with asymmetric and perturbed HI disks, previously unidentified companions, and ongoing interactions. One was found to have a polar HI disk with no stellar counterpart. While our small number statistics so far are limiting, results support past findings that most void galaxies are typically late type galaxies with gas rich disks and small scale clustering similar to field galaxies despite their large scale underdense environment.
We present a catalog of 8358 sources extracted from images produced by the Bolocam Galactic Plane Survey (BGPS). The BGPS is a survey of the millimeter dust continuum emission from the northern Galactic plane. The catalog sources are extracted using a custom algorithm, Bolocat, which was designed specifically to identify and characterize objects in the large-area maps generated from the Bolocam instrument. The catalog products are designed to facilitate follow-up observations of these relatively unstudied objects. The catalog is 98% complete from 0.4 Jy to 60 Jy over all object sizes for which the survey is sensitive (<3.5'). We find that the sources extracted can best be described as molecular clumps -- large dense regions in molecular clouds linked to cluster formation. We find the flux density distribution of sources follows a power law with dN/dS ~S^(-2.4 +/- 0.1) and that the mean Galactic latitude for sources is significantly below the midplane: <b>=(-0.095 +/- 0.001) deg.
We perform hydrodynamical simulations of major galaxy mergers using new methods for calculating the growth of massive black holes (BH) in galactic nuclei and their impact on the surrounding galaxy. We model BH growth by including a subgrid model for accretion produced by angular momentum transport on unresolved scales. The impact of the BHs radiation on surrounding gas is approximated by depositing momentum into the ambient gas, which produces an outward force away from the BH. We argue that these phenomenological models for BH growth and feedback better approximate the interaction between the BH and dense gas in galaxies than previous models. We show that this physics leads to self-regulated black hole growth: during the peak of activity, the accretion rate onto the BH is largely determined by the physics of BH feedback, not the subgrid accretion model. The BH significantly modifies the gas dynamics in the galactic nucleus (< 300 pc), but does not generate large-scale galactic outflows. Integrated over an entire galaxy merger, BH feedback has little effect on the total number of stars formed, but is crucial for setting the BHs mass.
We present a quantitative analysis of the SFH of 12 fields in the SMC. We
find that there are four main periods of enhancement of star formation: a young
one peaked at around 0.2-0.5 Gyr old, only present in the eastern and in the
central-most fields; two at intermediate ages present in all fields (a
conspicuous one peaked at 4-5 Gyr old, and a less significant one peaked at
1.5-2.5); and an old one, peaked at 10 Gyr in all fields but the western ones.
In the western fields, this old enhancement splits into two, one peaked at
around 8 Gyr old and another at around 12 Gyr old. This "two-enhancement" zone
seems to be a robust feature since it is unaffected by our choice of stellar
evolutionary library but more data covering other fields of the SMC are
necessary in order to ascertain its significancy.
Some correlation could exist with encounters taken from the orbit
determination of Kallivayalil et al. (2006). But our results would be also fit
in a first pericenter passage scenario like the one claimed by Besla et al.
(2007). There is a strong dichotomy between East/Southeast and West in the
current irregular shape of the SMC. We find that this dichotomy is produced by
the youngest population and began about 1 Gyr ago or later. We do not find yet
a region dominated by an old halo at 4.5 kpc from the SMC center, indicating
either that this old stellar halo does not exist in the SMC or that its
contribution to the stellar populations, at the galactocentric distances of our
outermost field, is negligible. We derive the age-metallicity relation and find
that the metallicity increased continuously from early epochs until now.
We present time series photometry of the M dwarf transiting exoplanet system GJ 436 obtained with the the EPOCh (Extrasolar Planet Observation and Characterization) component of the NASA EPOXI mission. We conduct a search of the high-precision time series for additional planets around GJ 436, which could be revealed either directly through their photometric transits, or indirectly through the variations these second planets induce on the transits of the previously known planet. In the case of GJ 436, the presence of a second planet is perhaps indicated by the residual orbital eccentricity of the known hot Neptune companion. We find no candidate transits with significance higher than our detection limit. From Monte Carlo tests of the time series, we rule out transiting planets larger than 1.0 R_Earth interior to GJ 436b with 95% confidence. Assuming coplanarity of additional planets with the orbit of GJ 436b, we cannot expect that putative planets with orbital periods longer than about 3.4 days will transit. However, if such a planet were to transit, we rule out planets larger than 1.5 R_Earth with orbital periods less than 13 days with 95% confidence. We also place dynamical constraints on additional bodies in the GJ 436 system. Our analysis should serve as a useful guide for similar analyses for which radial velocity measurements are not available, such as those discovered by the Kepler mission. These dynamical constraints on additional planets with periods from 0.5 to 9 days rule out coplanar secular perturbers as small as 10 M_Earth and non-coplanar secular perturbers as small as 1 M_Earth in orbits close in to GJ 436b. We present refined estimates of the system parameters for GJ 436. We also report a sinusoidal modulation in the GJ 436 light curve that we attribute to star spots. [Abridged]
A new mechanism is proposed by which short gamma-ray burst (SGRB) production can be achieved. In this new paradigm, it is supposed that the compact objects contained within a globular cluster (GC) interact through close encounters, rather than being driven together by pure gravitational wave emission in existing binaries. Here we perform a careful assessment of the relevant processes and stellar dynamics within GCs as these undergo core collapse over cosmic time. We show that such events are frequent enough in their cores to be consistent both with current observational rate demands for SGRB production and with the widening range of observed redshifts of the associated hosts. Precise modeling of the hydrodynamics allows for a detailed description of the encounter, and our calculations show that there is in principle no problem in accounting for the global energy budget of a typical SGRB. The particulars of each collision, are variable in several aspects, and can lead to interesting diversity. First, the characteristics of the encounter are highly dependent on the impact parameter. This is in contrast to the merger scenario, where the masses of the compact objects dictate a typical length and luminosity scale for SGRB activity. Second, the nature of the compact star itself can produce very different outcomes. Finally, the presence of tidal tails in which material will fall back onto the central object at a later time is a robust feature of the present set of calculations. The mass involved in these structures is considerably larger than for binary mergers. It is thus possible, in principle, to account generically in this scenario for a prompt episode of energy release as well as for activity many dynamical time scales later. (abridged)
The CMa R1 star-forming region contains several compact clusters as well as many young early-B stars. It is associated with a well-known bright rimmed nebula, the nature of which is unclear (fossil HII region or supernova remnant). To help elucidate the nature of the nebula, our goal was to reconstruct the star-formation history of the CMa R1 region, including the previously unknown older, fainter low-mass stellar population, using X-rays. We analyzed images obtained with the ROSAT satellite, covering ~5 sq. deg. Complementary VRI photometry was performed with the Gemini South telescope. Colour-magnitude and colour-colour diagrams were used in conjunction with pre-main sequence evolutionary tracks to derive the masses and ages of the X-ray sources. The ROSAT images show two distinct clusters. One is associated with the known optical clusters near Z CMa, to which ~40 members are added. The other, which we name the "GU CMa" cluster, is new, and contains ~60 members. The ROSAT sources are young stars with masses down to M_star ~0.5 M_sun, and ages up to 10 Myr. The mass functions of the two clusters are similar, but the GU CMa cluster is older than the cluster around Z CMa by at least a few Myr. Also, the GU CMa cluster is away from any molecular cloud, implying that star formation must have ceased; on the contrary (as already known), star formation is very active in the Z CMa region.
The development of Hybrid CMOS Detectors (HCDs) for X-Ray telescope focal planes will place them in con- tention with CCDs on future satellite missions due to their faster frame rates, flexible readout scenarios, lower power consumption, and inherent radiation hardness. CCDs have been used with great success on the current generation of X-Ray telescopes (e.g. Chandra, XMM, Suzaku, and Swift). However their bucket-brigade read-out architecture, which transfers charge across the chip with discrete component readout electronics, results in clockrate limited readout speeds that cause pileup (saturation) of bright sources and an inherent susceptibility to radiation induced displacement damage that limits mission lifetime. In contrast, HCDs read pixels with low power, on-chip multiplexer electronics in a random access fashion. Faster frame rates achieved with multi-output readout design will allow the next generation's larger effective area telescopes to observe bright sources free of pileup. Radiation damaged lattice sites effect a single pixel instead of an entire row. Random access, multi-output readout will allow for novel readout modes such as simultaneous bright-source-fast/whole-chip-slow readout. In order for HCDs to be useful as X-Ray detectors, they must show noise and energy resolution performance similar to CCDs while retaining advantages inherent to HCDs. We will report on readnoise, conversion gain, and energy resolution measurements of an X-Ray enhanced Teledyne HAWAII-1RG (H1RG) HCD and describe techniques of H1RG data reduction.
Using CARMA, we imaged the 87 GHz SiO v=0 J=2-1 line toward Orion-KL with 0.45 arcsec angular resolution. The maps indicate that radio source I drives a bipolar outflow into the surrounding molecular cloud along a NE--SW axis, in agreement with the model of Greenhill et al. (2004). The extended high velocity outflow from Orion-KL appears to be a continuation of this compact outflow. High velocity gas extends farthest along a NW--SE axis, suggesting that the outflow direction changes on time scales of a few hundred years.
We search for isolated galaxies using a volume-limited sample of galaxies with 0.02< z < 0.04742 from SDSS DR7 supplemented by bright galaxies. We devise a diagnostic tool to select isolated galaxies in different environments using the projected separation (r_p) normalized by the virial radius of the nearest neighbor (r_{vir,nei}) and the local background density. We find that the isolation condition of r_p>r_{vir,nei} and \rho <\bar{\rho} well segregates the CIG galaxies. We confirm the morphology conformity between the host and their satellites, which suggests importance of hydrodynamic interaction among galaxies within their virial radii in galaxy evolution.
The Galaxy Zoo citizen science website invites anyone with an Internet connection to participate in research by classifying galaxies from the Sloan Digital Sky Survey. As of April 2009, more than 200,000 volunteers had made more than 100 million galaxy classifications. In this paper, we present results of a pilot study into the motivations and demographics of Galaxy Zoo volunteers, and define a technique to determine motivations from free responses that can be used in larger multiple-choice surveys with similar populations. Our categories form the basis for a future survey, with the goal of determining the prevalence of each motivation.
We present abundances of Fe, Na, and O for 1409 red giant stars in 15 galactic globular clusters, derived from the homogeneous analysis of high resolution FLAMES/GIRAFFE spectra. Combining the present data with previous results, we obtained a total sample of 1958 stars in 19 clusters, the largest and most homogeneous database of this kind to date. Our GCs have [Fe/H] from -2.4 to -0.4, with a wide variety of global parameters (morphology of the horizontal branch, mass, concentration, etc). For all clusters we find the Na-O anticorrelation, the classical signature of proton-capture reactions in H-burning at high temperature in a previous generation of more massive stars, now extinct. Using quantitative criteria (from the morphology and extension of the Na-O anticorrelation), we can define 3 components of the stellar population in GCs: a primordial component (P) of first-generation stars, and 2 components of second-generation stars (intermediate I and extreme E populations from their different chemical composition). The P component is present in all GCs, and its fraction is almost constant at about one third. The I component represents the bulk of the cluster population. The E component is not present in all GCs, and it is more conspicuous in some (but not in all) of the most massive ones. We discuss the fractions and spatial distributions of these components in our sample and in two additional clusters (M3 and M13) from the literature. We also find that the slope of the anti-correlation (defined by the minimum O and maximum Na abundances) changes from cluster-to-cluster, a change that is represented well by a bilinear relation on cluster metallicity and luminosity. This second dependence suggests a correlation between average mass of polluters and cluster mass.
We present homogeneous abundances for Fe and some of the elements involved in the proton-capture reactions (O, Na, Mg, Al, and Si) for 202 red giants in 17 Galactic globular clusters (GCs) from the analysis of high resolution UVES spectra obtained with FLAMES@ESO-VLT2. Our programme clusters span almost the whole range in metallicity of GCs and were selected to sample the widest range of global parameters (HB morphology, masses, concentration, etc). Here we focus on the discussion of the Na-O and Mg-Al anticorrelations and related issues. Our study finds clear Na and O star-to-star abundance variations in all GCs. Variations in Al are present in all but a few GCs. Finally, a spread in abundances of Mg and Si are also present in a few clusters. Mg is slightly less overabundant and Si slightly more overabundant in the most Al-rich stars. The correlation between Si and Al abundances is a signature of production of 28Si leaking from the Mg-Al cycle in a few clusters. The cross sections required for the proper reactions to take over in the cycle point to temperatures in excess of about 65 MK for the favoured site of production. We used a dilution model to infer the total range of Al abundances starting from the Al abundances in the UVES spectra, and the Na abundance distributions found from analysis of the much larger set of stars for which GIRAFFE spectra were available. We found that the maximum amount of additional Al produced by first generation polluters contributing to the composition of the second generation stars in each cluster is closely correlated with the same combination of metallicity and cluster luminosity that reproduced the minimum O abundances found from GIRAFFE spectra. We then suggest that the high temperatures required for the Mg-Al cycle are only reached in the most massive and most metal-poor polluters.
We present Chandra ACIS-I and ACIS-S observations ($\sim$200 ks in total) of the X-ray luminous elliptical galaxy NGC 4636, located in the outskirts of the Virgo cluster. A soft band (0.5-2 keV) image shows the presence of a bright core in the center surrounded by an extended X-ray corona and two pronounced quasi-symmetric, 8 kpc long, arm-like features. Each of this features defines the rimof an ellipsoidal bubble. An additional bubble-like feature, whose northern rim is located $\sim2$ kpc south of the north-eastern arm, is detected as well. We present surface brightness and temperature profiles across the rims of the bubbles, showing that their edges are sharp and characterized by temperature jumps of about 20-25%. Through a comparison of the observed profiles with theoretical shock models, we demonstrate that a scenario where the bubbles were produced by shocks, probably driven by energy deposited off-center by jets, is the most viable explanation to the X-ray morphology observed in the central part of NGC 4636.
[abridged] We present the analysis of the X-ray brightness and temperature profiles for six clusters belonging to both the Cool Core and Non Cool Core classes, in terms of the Supermodel (SM) developed by Cavaliere, Lapi & Fusco-Femiano (2009). Based on the gravitational wells set by the dark matter halos, the SM straightforwardly expresses the equilibrium of the IntraCluster Plasma (ICP) modulated by the entropy deposited at the boundary by standing shocks from gravitational accretion, and injected at the center by outgoing blastwaves from mergers or from outbursts of Active Galactic Nuclei. The cluster set analyzed here highlights not only how simply the SM represents the main dichotomy Cool vs. Non Cool Core clusters in terms of a few ICP parameters governing the radial entropy run, but also how accurately it fits even complex brightness and temperature profiles. For Cool Core clusters like A2199 and A2597, the SM with a low level of central entropy straightforwardly yields the characteristic peaked profile of the temperature marked by a decline toward the center, without requiring currently strong radiative cooling and high mass deposition rates. Non Cool Core clusters like A1656 require instead a central entropy floor of a substantial level, and some like A2256 and even more A644 feature structured temperature profiles that also call for a definite floor extension; in such conditions the SM accurately fits the observations, and suggests that in these clusters the ICP has been just remolded by a merger event. The SM also predicts that dark matter halos with high concentration should correlate with flatter entropy profiles and steeper brightness in the outskirts; this is indeed the case with A1689.
Thanks to a variety of pertinent wide-angle facilities (WFI-slitless mode, VLT-FLAMES (Pasquini et al. 2002), SPITZER, 2MASS) it is possible to comprehensively study the nature of early-type objects in star-forming regions like the Eagle Nebula and Carina on large spatial scales. In them, the young open clusters NGC 6611, Trumpler 14, Trumpler 15, Trumpler 16, and their vicinities are of particular interest. With the WFI in its slitless mode (Baade et al. 1999), one can reliably and with little extra effort discriminate in thousands of spectra between intrinsic circumstellar emission as in HBe/Ae stars and diffuse interstellar line emission. The only bias results from the need of the equivalent width and absolute strength of the line emission to be sufficient for detection. VLT-FLAMES spectra combined with infrared data from SPITZER and 2MASS permit the nature of the objects with and without emission-lines to be derived. Following this approach, we report on the discovery and classification of new Herbig Be/Ae stars, pre-main sequence objects, and main sequence stars in these regions. Based on line-width measurements in VLT-FLAMES spectra, the evolution of the rotational velocities between pre-main sequence and main sequence phases is also discussed.
Optical CCD imaging with H$\alpha$ and [SII] filters and spectroscopic
observations of the galactic supernova remnant G85.9-0.6 have been performed
for the first time. The CCD image data are taken with the 1.5m Russian-Turkish
Telescope (RTT150) at TUBITAK National Observatory (TUG) and spectral data are
taken with the Bok 2.3 m telescope on Kitt Peak, AZ.
The images are taken with narrow-band interference filters H$\alpha$, [SII]
and their continuum. [SII]/H$\alpha$ ratio image is performed. The ratio
obtained from [SII]/H$\alpha$ is found to be $\sim$0.42, indicating that the
remnant interacts with HII regions. G85.9-0.6 shows diffuse-shell morphology.
[SII]$\lambda\lambda 6716/6731$ average flux ratio is calculated from the
spectra, and the electron density $N_{e}$ is obtained to be 395 $cm^{-3}$. From
[OIII]/H$\beta$ ratio, shock velocity has been estimated, pre-shock density of
$n_{c}=14$ $cm^{-3}$, explosion energy of $E=9.2\times10^{50}$ ergs,
interstellar extinction of $E(B-V)=0.28$, and neutral hydrogen column density
of $N(HI)=1.53\times10^{21}$ $cm^{-2}$ are reported.
We have observed the luminous (L_x ~ 6x10^44 erg/s) radio-quiet quasar RBS 1124 (z=0.208) with Suzaku. We report the detection of a moderately broad iron (Fe) line and of a weak soft X-ray excess. The X-ray data are very well described by a simple model comprising a power law X-ray continuum plus its reflection off the accretion disc. If the inner disc radius we measure (<=3.8 gravitational radii) is identified with the innermost stable circular orbit of the black hole spacetime, we infer that the black hole powering RBS 1124 is rotating rapidly with spin a>= 0.6. The soft excess contribution in the 0.5-2 keV band is ~15%, about half than that typically observed in unobscured Seyfert 1 galaxies and quasars, in line with the low disc reflection fraction we measure (R_disc ~0.4). The low reflection fraction cannot be driven by disc truncation which is at odds not only with the small inner disc radius we infer but, most importantly, with the radiatively efficient nature of the source (L_Bol / L_Edd ~1). A plausible explanation is that the X-ray corona is the base of a failed jet (RBS 1124 being radio-quiet) and actually outflowing at mildly relativistic speeds. Aberration reduces the irradiation of the disc, thus forcing a lower than standard reflection fraction, and halves the inferred source intrinsic luminosity, reducing the derived Eddington ratio from ~1to ~0.5. [abridged]
This research work is based on the study of the longitudinal distribution of the most active sunspot zones on the photosphere. Sunspot data has been analyzed for 12 solar cycles (cycles 12-23) separately for northern and southern hemisphere, and the entire solar sphere. The timelongitude diagrams and their corresponding histograms have been plotted to probe the formation, location, longitudinal spread, and lifetime of the most active sunspot longitudes. By the analysis and comparison of the time- longitude diagrams and histograms six active longitudes (>0, ~90, ~135, ~180, ~270 and <360 degrees) have been identified out of which three (~90, ~180 and ~270 degrees) are observed to be most frequent for the whole dataset analyzed. The comparison of the northern and southern hemisphere revealed that the hemispheres do not exhibit very similar kind of behavior. The lifetime and longitudinal spread of sunspot active longitudes is found to be 3-5 Carrington rotations and 20-30 degrees Carrington longitude respectively. This research work also includes the study of the movement of most active sunspot longitudes from higher to lower latitudes in northern hemispheres for six solar cycles (cycles 18-23). For this purpose the formation of sunspot active longitudes has been investigated in four latitudinal belts (40-30, 30-20, 20-10 and 10-0 degrees)). It is found that the sunspot active longitudes follow a certain longitudinal pattern during the evolution of the 11-year solar cycle. In the beginning of a solar cycle they seem to appear mostly around two longitudes ~0 degree and ~270 degrees in the latitudinal belt 40-30 degrees. As the solar cycle proceeds they tend to be stable around two longitudes ~90 degrees and ~270 degrees which are antipodal.
Total solar irradiance reconstructed between 1978 and 2003 using solar surface magnetic field distributions is compared with three composites of total solar irradiance measurements. A good correspondence is found with the total solar irradiance composite from PMOD/WRC, with no bias between the three cycles. The agreement with the other composites (the ACRIM composite, mainly based on the Active Cavity Radiometer Irradiance Monitors I, II & III, and the IRMB composite from the Institut Royal Meteorologique Belgique) is significantly poorer. In particular, a secular increase in the irradiance exhibited by these composites is not present in the reconstructions. Hence any secular trend in total solar irradiance between 1978 and 2003 is not due to magnetic fields at the solar surface.
The width (W), root mean squared amplitude (Rs) of lower and upper kHz quasi-periodic oscillations (QPOs) from accreting neutron stars vary with frequency. Similarly, the QPO frequency varies with the source count rate (S). Hence, the significance of a QPO, scaling as S x Rs^2/W^(1/2) will also depend on frequency. In addition, the significance also scales up with the square root of the integration time of the Fourier power density spectrum (T). Consequently, depending on the way data are considered, kHz QPOs may be detected only over a limited range of their frequency spans or detected predominantly at some frequencies, leading potentially to biases in the observed distributions of frequencies or frequency ratios. Although subject of much controversy, an observed clustering of QPO frequency ratios around 3/2 in Sco X-1, also seen in other sources, has been previously used as an argument supporting resonance based models of neutron star QPOs. In this paper, we measure how the statistical significance of both kHz QPOs vary with frequency for three prototype neutron star kHz QPO sources, namely 4U1636-536, 4U0614+091 and Sco X-1. As the significance of QPO detection depends on frequency, we show that in sensitivity-limited observations (as in the case of the RXTE/PCA), a simultaneous detection of both the lower and upper kHz QPOs can only be achieved over limited frequency ranges. As a result, even a uniform distribution of QPO frequencies will lead to peaks (in particular around 3/2) in the histogram of frequency ratios. This implies that the observed clustering of ratios does not provide any evidence for intrinsically preferred frequency ratios, thus weakening the case for a resonance mechanism at the origin of neutron star kHz QPOs.
We study a model of $F(R)$ gravity in which a crossing of the phantom divide can be realized. In particular, we demonstrate the behavior of $F(R)$ gravity around a crossing of the phantom divide by taking into account the presence of cold dark matter.
We study power density spectra (PDS) of X-ray flux variability in binary systems where the accretion flow is truncated by the magnetosphere. PDS of accreting X-ray pulsars where the neutron star is close to the corotation with the accretion disk at the magnetospheric boundary, have a distinct break/cutoff at the neutron star spin frequency. This break can naturally be explained in the "perturbation propagation" model, which assumes that at any given radius in the accretion disk stochastic perturbations are introduced to the flow with frequencies characteristic for this radius. These perturbations are then advected to the region of main energy release leading to a self-similar variability of X-ray flux P~f^{-1...-1.5}. The break in the PDS is then a natural manifestation of the transition from the disk to magnetospheric flow at the frequency characteristic for the accretion disk truncation radius (magnetospheric radius). The proximity of the PDS break frequency to the spin frequency in corotating pulsars strongly suggests that the typical variability time scale in accretion disks is close to the Keplerian one. In transient accreting X-ray pulsars characterized by large variations of the mass accretion rate during outbursts, the PDS break frequency follows the variations of the X-ray flux, reflecting the change of the magnetosphere size with the accretion rate. Above the break frequency the PDS steepens to ~f^{-2} law which holds over a broad frequency range. These results suggest that strong f^{-1...-1.5} aperiodic variability which is ubiquitous in accretion disks is not characteristic for magnetospheric flows.
We present a new computer code for modeling magnetized neutron star
atmospheres in a wide range of magnetic fields (10^{12} - 10^{15} G) and
effective temperatures (3 \times 10^5 - 10^7 K). The atmosphere is assumed to
consist either of fully ionized electron-ion plasmas or of partially ionized
hydrogen. Vacuum resonance and partial mode conversion are taken into account.
Any inclination of the magnetic field relative to the stellar surface is
allowed. We use modern opacities of fully or partially ionized plasmas in
strong magnetic fields and solve the coupled radiative transfer equations for
the normal electromagnetic modes in the plasma. Using this code, we study the
possibilities to explain the soft X-ray spectra of isolated neutron stars by
different atmosphere models.
In particular, the outgoing spectrum using the "sandwich" model (thin
atmosphere with a hydrogen layer above a helium layer) is constructed. Thin
partially ionized hydrogen atmospheres with vacuum polarization are shown to be
able to improve our understanding of the observed spectrum of the nearby
isolated neutron star RBS 1223 (RX J1308.8+2127).
There is compelling evidence that black holes (BHs) in cluster centers vigorously interact with their surroundings, indicating that any realistic model of cluster formation needs to account for these processes. Here we use high-resolution cosmological simulations of a large cluster and group sample to study how BHs affect their host systems. We focus on two specific properties, the halo gas fraction and the X-ray luminosity-temperature scaling relation, both of which are notoriously difficult to reproduce in self-consistent hydrodynamical simulations. We show that BH feedback can solve both of these issues, bringing them in excellent agreement with observations, without alluding to the `cooling only' solution that produces unphysically bright central galaxies.
Results from simulations of hierarchical structure formation cosmology provide a tool to develop an evolutionary model of regular magnetic fields coupled to galaxy formation and evolution. We use the dynamo theory to derive the timescales of amplification and ordering of magnetic fields in disk and puffy galaxies. Galaxies similar to the Milky Way formed their disks at $z\approx10$ and regular fields of $\mu$G strength and a few kpc coherence length were generated within 2 Gyr (at $z\approx3$), but field ordering up to the coherence scale of the galaxy size took another 6 Gyr (at $z\approx0.5$). Giant galaxies formed their disk already at $z\approx10$, allowing more efficient dynamo generation of strong regular fields (with kpc coherence length) already at $z\approx4$. Dwarf galaxies should have hosted fully coherent fields at $z\approx1$. This evolutionary scenario and number of predictions of the model can be tested by measurements of polarized synchrotron emission and Faraday rotation with the planned Square Kilometre Array. This model is used to simulate the evolution of regular fields in disk galaxies and the polarized radio sky as part of the Square Kilometer Array Design Studies (SKADS).
We consider the dependence of ultra-high energy cosmic ray (UHECR) flux predictions on the choice of galaxy catalogue. We demonstrate that model predictions by Koers & Tinyakov (2009b), based on the so-called KKKST catalogue, are in good agreement with predictions based on the XSCz catalogue, a recently compiled catalogue that contains spectroscopic redshifts for a large fraction of galaxies. This agreement refutes the claim by Kashti (2009) that the KKKST catalogue is not suited for studies of UHECR anisotropy due to its dependence on photometric redshift estimates. In order to quantify the effect of galaxy catalogues on flux predictions, we develop a measure of anisotropies associated with model flux maps. This measure offers a general criterion to study the effect of model parameters and assumptions on the predicted strength of UHECR anisotropies.
Using N-body simulations of shell galaxies created in nearly radial minor mergers, we investigate the error of collision dating, resulting from the neglect of dynamical friction and of gradual disruption of the cannibalized dwarf.
The cosmic acceleration is one of the most significant cosmological discoveries over the last century. Following the more accurate data a more dramatic result appears: the recent analysis of the observation data (especially from SNe Ia) indicate that the time varying dark energy gives a better fit than a cosmological constant, and in particular, the equation of state parameter $w$ (defined as the ratio of pressure to energy density) crosses -1 at some low redshift region. This crossing behavior is a serious challenge to fundamental physics. In this article, we review a number of approaches which try to explain this remarkable crossing behavior. First we show the key observations which imply the crossing behavior. And then we concentrate on the theoretical progresses on the dark energy models which can realize the crossing -1 phenomenon. We discuss three kinds of dark energy models: 1. two-field models (quintom-like), 2. interacting models (dark energy interacts with dark matter), and 3. the models in frame of modified gravity theory (concentrating on brane world).
The structure and kinematics of the recognized stellar components of the Milky Way are explored, based on well-determined atmospheric parameters and kinematic quantities for 32360 "calibration stars" from the Sloan Digital Sky Survey (SDSS) and its first extension, (SDSS-II), which included the sub-survey SEGUE: Sloan Extension for Galactic Understanding and Exploration. Full space motions for a sub-sample of 16920 stars, exploring a local volume within 4 kpc of the Sun, are used to derive velocity ellipsoids for the inner- and outer-halo components of the Galaxy, as well as for the canonical thick-disk and proposed metal-weak thick-disk populations. We first examine the question of whether the data require the presence of at least a two-component halo in order to account for the rotational behavior of likely halo stars in the local volume, and whether more than two components are needed. We also address the question of whether the metal-weak thick disk is kinematically and chemically distinct from the canonical thick disk. In addition, we consider the fractions of each component required to understand the nature of the observed kinematic behavior of the stellar populations of the Galaxy as a function of distance from the plane. Scale lengths and scale heights for the thick-disk and metal-weak thick-disk components are determined. Spatial density profiles for the inner- and outer-halo populations are inferred from a Jeans Theorem analysis. The full set of calibration stars (including those outside the local volume) is used to test for the expected changes in the observed stellar metallicity distribution function with distance above the Galactic plane in-situ, due to the changing contributions from the underlying stellar populations. [abridged]
To understand the processes that build up galaxies we investigate the stellar structure and gas kinematics of spiral and irregular galaxies out to redshift 1. We target 92 galaxies in four cluster (z = 0.3 & 0.5) fields to study the environmental influence. Their stellar masses derived from multiband VLT/FORS photometry are distributed around but mostly below the characteristic Schechter-fit mass. From HST/ACS images we determine morphologies and structural parameters like disk length, position angle and ellipticity. Combining the spectra of three slit positions per galaxy using the MXU mode of VLT/FORS2 we construct the two-dimensional velocity field from gas emission lines for 16 cluster members and 33 field galaxies. The kinematic position angle and flatness are derived by a Fourier expansion of elliptical velocity profiles. To trace possible interaction processes, we define three irregularity indicators based on an identical analysis of local galaxies from the SINGS project. Our distant sample displays a higher fraction of disturbed velocity fields with varying percentages (10%, 30% and 70%) because they trace different features. While we find far fewer candidates for major mergers than the SINS sample at z~2, our data are sensitive enough to trace less violent processes. Most irregular signatures are related to star formation events and less massive disks are affected more than Milky-Way type objects. We detect similarly high fractions of irregular objects both for the distant field and cluster galaxies with similar distributions. We conclude that we may witness the building-up of disk galaxies still at redshifts z~0.5 via minor mergers and gas accretion, while some cluster members may additionally experience stripping, evaporation or harassment interactions.
We use deep HST/ACS F555W and F814W photometry of resolved stars in the M81 Group dwarf irregular galaxy Ho II to study the hypothesis that the holes identified in the neutral ISM (HI) are created by stellar feedback. From the deep photometry, we construct color-magnitude diagrams (CMDs) and measure the star formation histories (SFHs) for stars contained in HI holes from two independent holes catalogs, as well as select control fields, i.e., similar sized regions that span a range of HI column densities. Converting the recent SFHs into stellar feedback energies, we find that enough energy has been generated to have created all holes. However, the required energy is not always produced over a time scale that is less than the estimated kinematic age of the hole. The combination of the CMDs, recent SFHs, and locations of young stars shows that the stellar populations inside HI holes are not coherent, single-aged, stellar clusters, as previously suggested, but rather multi-age populations distributed across each hole. From a comparison of the modeled and observed integrated magnitudes, and the locations and energetics of stars inside of HI holes, we propose a potential new model: a viable mechanism for creating the observed HI holes in Ho II is stellar feedback from multiple generations of SF spread out over tens or hundreds of Myr, and thus, the concept of an age for an HI hole is intrinsically ambiguous. We further find that \halpha and 24 micron emission, tracers of the most recent star formation, do not correlate well with the positions of the HI holes. However, UV emission, which traces star formation over roughly the last 100 Myr, shows a much better correlation with the locations of the HI holes.
NGC6611, Trumpler 14, Trumpler 15, Trumpler 16, Collinder 232 are very young open clusters located in star-formation regions of the Eagle Nebula or the Carina in the MW, and NGC346 in the SMC. With different instrumentations and techniques, it was possible to detect and classify new Herbig Ae/Be stars, classical Be stars and to provide new tests / comparisons about the Be stars appearance models. Special stars (He-strong) of these star-formation regions are also presented.
We present the results of VLBI and MERLIN observations of the massive disk galaxy IC 2497. Optical observations of IC 2497 revealed the existence of a giant emission nebula "Hanny's Voorwerp" in the proximity of the galaxy. Earlier short-track 18 cm observations with e-VLBI at 18 cm, detected a compact radio component (C1) at the centre of IC 2497. The brightness temperature of C1 was measured to be greater than 4E5 K. Deeper, long-track e-VLBI observations presented here, re-confirm the existence of C1 but also reveal the existence of a second compact component (C2) located about 230 milliarcseconds to the North-East of C1. The brightness temperature of C2 is measured to be greater than 1.4E5 K, suggesting that both components may be related to AGN activity (e.g. a radio core and jet hotspot). Lower resolution 18cm MERLIN observations show both components. C1 is shown to be compact with a slight elongation along the direction of Hanny's Voorwerp, and C2 shows a lot of extended emission in an almost perpendicular direction to the direction of the Voorwerp. Our results continue to support the hypothesis that IC 2497 contains an Active Galactic Nucleus (AGN), and that a jet associated with this AGN clears a path that permits ionising radiation from the AGN to directly illuminate the emission nebula.
In low-collisionality plasmas, anisotropic heat conduction due to a magnetic field leads to buoyancy instabilities for any nonzero temperature gradient. We study analogous instabilities in degenerate {\it collisional} plasmas, i.e., when the electron collision frequency is large compared to the electron cyclotron frequency. Although heat conduction is nearly isotropic in this limit, the small residual anisotropy ensures that collisional degenerate plasmas are also convectively unstable independent of the sign of the temperature gradient. We show that the range of wavelengths that are unstable is independent of the magnetic field strength, while the growth time increases with decreasing magnetic field strength. We discuss the application of these collisional buoyancy instabilities to white dwarfs and neutron stars. Magnetic tension and the low specific heat of a degenerate plasma significantly limit their effectiveness; the most promising venues for growth are in the liquid oceans of young, weakly magnetized neutron stars ($B \lesssim 10^9$ G) and in the cores of young, high magnetic field white dwarfs ($B \sim 10^9$ G).
(abridged)The majority of Active Galactic Nuclei (AGN) suffer from significant obscuration by surrounding dust and gas. X-ray surveys in the 2-10 keV band will miss the most heavily-obscured AGN in which the absorbing column density exceeds $\sim10^{24}$cm$^{-2}$ (the Compton-thick AGN). It is therefore vital to know the fraction of AGN that are missed in such X-rays surveys and to determine if these AGN represent some distinct population in terms of the fundamental properties of AGN and/or their host galaxies. In this paper we present the analysis of \textit{XMM-Newton} X-ray data for a complete sample of 17 low-redshift Type 2 Seyfert galaxies chosen from the Sloan Digital Sky Survey based solely on the high observed flux of the [OIII]$\lambda$5007 emission-line. This line is formed in the Narrow Line Region hundreds of parsecs away from the central engine. Thus, unlike the X-ray emission, it is not affected by obscuration due to the torus surrounding the black hole. It therefore provides a useful isotropic indicator of the AGN luminosity. As additional indicators of the intrinsic AGN luminosity, we use the Spitzer Space Telescope to measure the luminosities of the mid-infrared continuum and the [OIV]25.89$\mu$m narrow emission-line. We then use the ratio of the 2-10 keV X-ray luminosity to the [OIII], [OIV], and mid-infrared luminosities to assess the amount of X-ray obscuration and to distinguish between Compton-thick and Compton-thin objects. We find that the majority of the sources suffer significant amounts of obscuration: the observed 2-10 keV emission is depressed by more than an order-of-magnitude in 11 of the 17 cases (as expected for Compton-thick sources).
Different sequences of ellipsoids are represented on the ellipticity-rotation plane. The rotation parameter is defined as the ratio of kinetic energy related to the mean tangential equatorial velocity component to kinetic energy related to tangential equatorial component velocity dispersion and residual motions. Systems with isotropic stress tensor are considered as adjoint configurations to their counterparts with anisotropic stress tensor, different angular momentum, and equal remaining parameters. Both nonequilibrium figures and figures elongated by imaginary rotation are represented on the ellipticity-rotation plane. An application is made to a reduced sample of elliptical galaxies. The position on the ellipticity-rotation plane of both sample objects and related adjoint configurations with isotropic stress tensor is inferred from existing observations within the SAURON project. With a single exception, slow rotators are characterized by low ellipticities, low anisotropy parameters, and low rotation parameters, while the contrary holds for fast rotators. A possible interpretation of slow rotators as nonrotating at all and elongated due to negative anisotropy parameters, is exploited. Finally, the elliptical side of the Hubble sequence is interpreted as a sequence of equilibrium (adjoint) configurations where the ellipticity is an increasing function of the rotation parameter, slow rotators correspond to early classes and fast rotators to late classes. In this view, boundaries are rotationally distorted regardless of angular momentum and stress tensor, where rotation has to be intended as due to additional kinetic energy of tangential equatorial velocity components, with respect to spherical configurations with isotropic stress tensor.
The observed distribution of globular cluster binary radio pulsars in the eccentricity versus orbital period plane can be explained as a result of binary-single star interactions. Our numerical and analytical study hints that the highest eccentricity binaries in clusters are likely to be from exchange and/or merger of a single star with a binary component, while the intermediate eccentricity systems are probably results of fly-by interactions.
With the recent torrent of discoveries of new transiting planets, there have been ample candidates for observations using the Spitzer Space Telescope. We present here the results of our observations of TrES-2 using the Infrared Array Camera on Spitzer. We monitored this transiting system during two secondary eclipses, when the planetary emission is blocked by the star. The resulting decrease in flux is 0.127%+-0.021%, 0.230%+-0.024%, 0.199%+-0.054%, and 0.359%+-0.060%, at 3.6, 4.5, 5.8, and 8.0 microns, respectively. We show that three of these flux contrasts are well fit by a black body spectrum with Teff = 1500 K, as well as by a more detailed model spectrum of a planetary atmosphere. However, the planet-to-star flux ratio at 4.5 microns exceeds the expectation from the blackbody emission, which argues for a temperature inversion in the atmosphere of TrES-2. The presence or absence of such an inversion in a planetary atmosphere has been predicted to be correlated with the amount of incident flux received by the planet, with hotter planets like TrES-2 being more likely to exhibit this inversion. Our observation of emission at 4.5 microns that is indicative of an inversion supports the proposed importance of TiO and VO opacities in atmospheric models of highly irradiated gas giants. Furthermore, we find that the times of the secondary eclipses are consistent with previously published times of transit and the expectation from a circular orbit. This implies that TrES-2 most likely has a circular orbit, and thus does not obtain additional thermal energy from tidal dissipation of a non-zero orbital eccentricity, a proposed explanation for the large radius of this planet.
We present a sample of 75 extinction curves derived from FUSE far-ultraviolet spectra supplemented by existing IUE spectra. The extinction curves were created using the standard pair method based on a new set of dereddened FUSE+IUE comparison stars. Molecular hydrogen absorption features were removed using individualized H_2 models for each sightline. The general shape of the FUSE extinction (8.4 micron^-1 < lambda^-1 < 11 micron^-1) was found to be broadly consistent with extrapolations from the IUE extinction (3.3 micron-1 < lambda^-1 < 8.6 micron^-1) curve. Significant differences were seen in the strength of the far-UV rise and the width of the 2175 A bump. All the FUSE+IUE extinction curves had positive far-UV slopes giving no indication that the far-UV rise was turning over at the shortest wavelengths. The dependence of A(lambda)/A(V) versus R(V)^-1 in the far-UV using the sightlines in our sample was found to be stronger than tentatively indicated by previous work. We present an updated R(V) dependent relationship for the full UV wavelength range (3.3 micron^-1 <= lambda^-1 <= 11 micron^-1). Finally, we searched for discrete absorption features in the far-ultraviolet. We found a 3 sigma upper limit of ~0.12 A(V) on features with a resolution of 250 (~4 A width) and 3 sigma upper limits of ~0.15 A(V) for lambda^-1 < 9.6 micron^-1 and ~0.68 A(V) for lambda^-1 > 9.6 micron^-1 on features with a resolution of 10^4 (~0.1 A width).
We investigate the properties of 12 ultra-massive passively evolving early type galaxies (ETGs) at z_phot>1.4 in the COSMOS 2 deg^2 field. These 12 ETGs were selected as pBzKs, have accurate 1.4<= z_phot <=1.7,high Sersic index profiles typical of ellipticals, no detection at 24 micron, resulting in a complete ETG sample at M*>2.5x10^11 M_sun (Chabrier IMF). Contrary to previous claims, the half light radii estimated in very high S/N imaging data from HST+ACS are found to be large for most of the sample, consistent with local ellipticals. If the high redshift ETGs with M*<2.5x10^11 M_sun are really small in size and compact as reported in previous studies, our result may suggest a "downsizing" scenario, whereby the most massive ETGs reach their final structure earlier and faster than lower mass ones. However, simulating galaxies with morphological properties fixed to those of local ETGs with the same stellar mass show that the few compact galaxies that we still recover in our sample can be understood in term of fluctuations due to noise preventing the recovery of the extended low surface brightness halos in the light profile. Such halos, typical of Sersic profiles, extending even up to 40 kpc, are indeed seen in our sample.
Including lowest loop correction, the black-body radiation via the Born-Infeld theory of electrodynamics is obtained. The possible direct implications of the results on Cosmic Microwave Background map is argued.
We review the paradigm of quintom cosmology. This scenario is motivated by the observational signal that the equation of state of dark energy across the cosmological constant boundary is mildly favored. As a theoretical setup we introduce a no-go theorem existing in quintom cosmology, and based on it we discuss the realizations of various quintom models. Additionally, we study the outsets and fates of a universe in quintom cosmology. Finally, we give a detailed presentation of dark energy perturbations in quintom cosmology and their effects on current observations.
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We present measurements of Fe, Mg, Si, Ca, and Ti abundances for 388 radial velocity member stars in the Sculptor dwarf spheroidal galaxy (dSph), a satellite of the Milky Way. This is the largest sample of individual alpha element (Mg, Si, Ca, Ti) abundance measurements in any single dSph. The measurements are made from Keck/DEIMOS medium-resolution spectra (6400-9000 A, R ~ 6500). Based on comparisons to published high-resolution (R >~ 20000) spectroscopic measurements, our measurements have uncertainties of sigma([Fe/H]) = 0.14 and sigma([alpha/Fe]) = 0.13. The Sculptor [Fe/H] distribution has a mean <[Fe/H]> = -1.58 and is asymmetric with a long, metal-poor tail, indicative of a history of extended star formation. Sculptor has a larger fraction of stars with [Fe/H] < -2 than the Milky Way halo. We have discovered one star with [Fe/H] = -3.80 +/- 0.28, which is the most metal-poor star known anywhere except the Milky Way halo, but high-resolution spectroscopy is needed to measure this star's detailed abundances. As has been previously reported based on high-resolution spectroscopy, [alpha/Fe] in Sculptor falls as [Fe/H] increases. The metal-rich stars ([Fe/H] ~ -1.5) have lower [alpha/Fe] than Galactic halo field stars of comparable metallicity. This indicates that star formation proceeded more gradually in Sculptor than in the Galactic halo. We also observe radial abundance gradients of -0.030 +/- 0.003 dex per arcmin in [Fe/H] and +0.013 +/- 0.003 dex per arcmin in [alpha/Fe] out to 11 arcmin (275 pc). Together, these measurements cast Sculptor and possibly other surviving dSphs as representative of the dwarf galaxies from which the metal-poor tail of the Galactic halo formed.
Since the first discovery of an extrasolar planetary system more than a decade ago, hundreds more have been discovered. Surprisingly, many of these systems harbor Jupiter-class gas giants located close to the central star, at distances of 0.1 AU or less. Observations of chromospheric 'hot spots' that rotate in phase with the planetary orbit, and elevated stellar X-ray luminosities,suggest that these close-in planets significantly affect the structure of the outer atmosphere of the star through interactions between the stellar magnetic field and the planetary magnetosphere. Here we carry out the first detailed three-dimensional MagnetoHydroHynamics (MHD) simulation containing the two magnetic bodies and explore the consequences of such interactions on the steady-state coronal structure. The simulations reproduce the observable features of 1) increase in the total X-ray luminosity, 2) appearance of coronal hot spots, and 3) phase shift of these spots with respect to the direction of the planet. The proximate cause of these is an increase in the density of coronal plasma in the direction of the planet, which prevents the corona from expanding and leaking away this plasma via a stellar wind. The simulations produce significant low temperature heating. By including dynamical effects, such as the planetary orbital motion, the simulation should better reproduce the observed coronal heating.
On 13 February 2009, a coronal wave -- CME -- dimming event was observed in
quadrature by the STEREO spacecraft. We analyze this event using a
three-dimensional, global magnetohydrodynamic (MHD) model for the solar corona.
The numerical simulation is driven and constrained by the observations, and
indicates where magnetic reconnection occurs between the expanding CME core and
surrounding environment. We focus primarily on the lower corona, extending out
to $3R_{\odot}$; this range allows simultaneous comparison with both EUVI and
COR1 data. Our simulation produces a diffuse coronal bright front remarkably
similar to that observed by STEREO/EUVI at 195 \AA. It is made up of \emph{two}
components, and is the result of a combination of both wave and non-wave
mechanisms.
The CME becomes large-scale quite low ($<$ 200 Mm) in the corona. It is not,
however, an inherently large-scale event; rather, the expansion is facilitated
by magnetic reconnection between the expanding CME core and the surrounding
magnetic environment. In support of this, we also find numerous secondary
dimmings, many far from the initial CME source region. Relating such dimmings
to reconnecting field lines within the simulation provides further evidence
that CME expansion leads to the "opening" of coronal field lines on a global
scale. Throughout the CME expansion, the coronal wave maps directly to the CME
footprint.
Our results suggest that the ongoing debate over the "true" nature of diffuse
coronal waves may be mischaracterized. It appears that \emph{both} wave and
non-wave models are required to explain the observations and understand the
complex nature of these events.
Galaxies moving through the intracluster medium (ICM) of a cluster of galaxies can lose gas via ram pressure stripping. This stripped gas forms a tail behind the galaxy which is potentially observable. In this paper, we carry out hydrodynamical simulations of a galaxy undergoing stripping with a focus on the gas properties in the wake and their observational signatures. We include radiative cooling in an adaptive hydrocode in order to investigate the impact of a clumpy, multi-phase interstellar medium. We find that including cooling results in a very different morphology for the gas in the tail, with a much wider range of temperatures and densities. The tail is significantly narrower in runs with radiative cooling, in agreement with observed wakes. In addition, we make detailed predictions of H I, Halpha and X-ray emission for the wake, showing that we generally expect detectable H I and Halpha signatures, but no observable X-ray emission (at least for our chosen ram-pressure strength and ICM conditions). We find that the relative strength of the Halpha diagnostic depends somewhat on our adopted minimum temperature floor (below which we set cooling to zero to mimic physics processes not included in the simulation).
(Abridged) This is the first of a series of papers in which we derive simultaneous constraints on cosmological parameters and X-ray scaling relations using observations of the growth of massive, X-ray flux-selected galaxy clusters. Our data set consists of 238 clusters drawn from the ROSAT All-Sky Survey, and incorporates extensive follow-up observations using the Chandra X-ray Observatory. Here we describe and implement a new statistical framework required to self-consistently produce simultaneous constraints on cosmology and scaling relations from such data, and present results on models of dark energy. In spatially flat models with a constant dark energy equation of state, w, the cluster data yield Omega_m=0.23 +- 0.04, sigma_8=0.82 +- 0.05, and w=-1.01 +- 0.20, marginalizing over conservative allowances for systematic uncertainties. These constraints agree well and are competitive with independent data in the form of cosmic microwave background (CMB) anisotropies, type Ia supernovae (SNIa), cluster gas mass fractions (fgas), baryon acoustic oscillations (BAO), galaxy redshift surveys, and cosmic shear. The combination of our data with current CMB, SNIa, fgas, and BAO data yields Omega_m=0.27 +- 0.02, sigma_8=0.79 +- 0.03, and w=-0.96 +- 0.06 for flat, constant w models. For evolving w models, marginalizing over transition redshifts in the range 0.05-1, we constrain the equation of state at late and early times to be respectively w_0=-0.88 +- 0.21 and w_et=-1.05 +0.20 -0.36. Our results highlight the power of X-ray studies, which enable the straightforward production of large, complete, and pure cluster samples and admit tight scaling relations, to constrain cosmology. However, the new statistical framework we apply to this task is equally applicable to cluster studies at other wavelengths.
(Abridged) This is the second in a series of papers in which we derive simultaneous constraints on cosmology and X-ray scaling relations using observations of massive, X-ray flux-selected galaxy clusters. The data set consists of 238 clusters drawn from the ROSAT All-Sky Survey with 0.1-2.4 keV luminosities >2.5e44 erg/second, and incorporates extensive follow-up observations using the Chandra X-ray Observatory. Our analysis accounts self-consistently for all selection effects, covariances and systematic uncertainties. Here we describe the reduction of the follow-up X-ray observations, present results on the cluster scaling relations, and discuss their implications. Our constraints on the luminosity-mass and temperature-mass relations, measured within r_500, lead to three important results. First, the data support the conclusion that excess heating of the intracluster medium has altered its thermodynamic state from that expected in a simple, gravitationally dominated system; however, this excess heating is primarily limited to the central regions of clusters (r<0.15r_500). Second, the intrinsic scatter in the center-excised luminosity-mass relation is remarkably small, being undetected at the <5% level in current data; for the hot, massive clusters under investigation, this scatter is smaller than in either the temperature-mass or Y_X-mass relations (10-15%). Third, the evolution with redshift of the scaling relations is consistent with the predictions of simple, self-similar models of gravitational collapse, indicating that the mechanism responsible for heating the central regions of clusters was in operation before redshift 0.5 (the limit of our data) and that its effects on global cluster properties have not evolved strongly since then.
We outline a new method to derive a "snapshot" metallicity estimate of
stellar systems (providing one resolves at least the brightest part of the CMD)
just on the basis of low-resolution (i.e., 6-8A FWHM) spectroscopy of a small
stellar sample. Our method relies on the Fe5270 Lick index measurements and
takes advantage of the special behavior of this spectral feature, that reaches
its maximum strength among the ubiquitous component of K-type giants. This
makes the Fe5270(max} estimate a robust and model-independent tracer of cluster
[Fe/H], being particularly insensitive to the age of the stellar population.
A comparison of the Fe5270(max) distribution derived from globular and open
clusters, as well as from the field giant population in the Galaxy disk,
confirms a tight correlation of the index maximum vs. cluster [Fe/H] allover
the entire metallicity range for stellar population with [Fe/H] >~ -2.0.
Relying on a theoretical calibration of the feature, we trust to effectively
infer cluster metallicity within a typical uncertainty of 0.1-0.2dex, depending
on RGB luminosity sampling of the observations.
We present a coherent stellar and nebular model reproducing the observations of the Planetary Nebula IC418. We want to test whether a stellar model obtained by fitting the stellar observations is able to satisfactory ionize the nebula and reproduce the nebular observations, which is by no mean evident. This allows us to determine all the physical parameters of both the star and the nebula, including the abundances and the distance. We used all the observational material available (FUSE, IUE, STIS and optical spectra) to constrain the stellar atmosphere model performed using the CMFGEN code. The photoionization model is done with Cloudy_3D, and is based on CTIO, Lick, SPM, IUE and ISO spectra as well as HST images. More than 140 nebular emission lines are compared to the observed intensities. We reproduce all the observations for the star and the nebula. The 3D morphology of the gas distribution is determined. The effective temperature of the star is 36.7kK. Its luminosity is 7700 solar luminosity. We describe an original method to determine the distance of the nebula using evolutionary tracks. No clumping factor is need to reproduce the age-luminosity relation. The distance of 1.25 kpc is found in very good agreement with recent determination using parallax method. The chemical composition of both the star and the nebula are determined. Both are Carbon-rich. The nebula presents evidence of depletion of elements Mg, Si, S, Cl (0.5 dex lower than solar) and Fe (2.9 dex lower than solar). This is the first self-consistent stellar and nebular model for a Planetary Nebula that reproduces all the available observations ranging from IR to UV, showing that the combined approach for the modeling process leads to more restrictive constraints and, in principle, more trustworthy results.
The stellar mass in galaxies scales approximately with the fourth power of the rotation velocity, and the masses of the central black holes in galactic nuclei scale approximately with the fourth power of the bulge velocity dispersion. It is shown here that these relations can be accounted for if, in a forming galaxy with an isothermal mass distribution, gas with a column density above about 8 Msun/pc^2 goes into stars while gas with a column density above about 2 g/cm^2 (10^4 Msun/pc^2) goes into a central black hole. The lower critical value is close to the column density of about 10 Msun/pc^2 at which atomic gas becomes molecular, and the upper value agrees approximately with the column density of about 1 g/cm^2 at which the gas becomes optically thick to its cooling radiation. These results are plausible because molecule formation is evidently necessary for star formation, and because the onset of a high optical depth in a galactic nucleus may suppress continuing star formation and favour the growth of a central black hole.
In cold dark matter cosmologies, the most massive dark matter halos undergo rapid growth between a redshift of z=1 and z=0, corresponding to the past 7 billion years of cosmic time. There is thus an expectation that the stellar masses of the most massive galaxies will also rapidly grow via merging over this redshift range. While there are examples of massive merging galaxies at low redshift, recent observations show that the stellar masses of massive galaxies have grown by only 30% since z=1. Some of the literature claims that the slow growth of massive galaxies is contrary to the CDM paradigm, although this is not necessarily the case. To determine why massive galaxies are not growing rapidly, we have modeled how galaxies populate dark matter halos. To do this, we have measured the space density and spatial clustering of redshift z<1 galaxies in the Bootes field of the NOAO Deep Wide-Field Survey. We have then modeled the observations using the halo occupation distribution (HOD) formalism. We find that the stellar masses of the largest galaxies are proportional to dark matter halo mass to the power of a third. In the most massive dark matter halos, we also find that the stellar mass is distributed mostly among "satellite" galaxies. As a consequence, the stellar masses of large galaxies are expected to increase relatively slowly, even though they reside within rapidly growing dark matter halos.
The Low Frequency Array (LOFAR) is a new generation of electronic radio telescope based on aperture array technology and working in the frequency range of 30-240 MHz. The telescope is being developed by ASTRON, and currently being rolled-out across the Netherlands and other countries in Europe. The plan is to build at least 36 stations in the Netherlands (with baseline lengths of up to 100 km), 5 stations in Germany, and 1 station in each of Sweden, France and the UK. With baseline lengths of up to 2000 km, sub-arcsecond resolution will be possible at the highest frequencies. The Key Science Projects being addressed by the project include: deep, wide-field cosmological surveys, transients, the epoch of re-ionisation and cosmic ray studies. We present the current status of the project, including the development of the super-core in Exloo and the completion of the first 3 stations. 'First fringes' from these stations is also presented.
We present a new sample of 25 fossil groups (FGs) at z < 0.1, along with a control sample of seventeen bright ellipticals located in non-fossil systems. Both the global properties of FGs (e.g. X-ray luminosity) as well as the photometric properties (i.e. isophotal shape parameter, a4) and spectroscopic parameters (e.g. the alpha-enhancement) of their first-ranked ellipticals are consistent with those of the control sample. This result favors a scenario where FGs are not a distinct class of systems, but rather a common phase in the life of galaxy groups. We also find no evidence for an evolutionary sequence explaining the formation of galaxies in fossil systems through the merging of galaxies in compact groups.
Recent wide-field imaging observations of the X-ray luminous cluster RDCSJ1252.9-2927 at z=1.24 uncovered several galaxy groups that appear to be embedded in filamentary structure extending from the cluster core. We make a spectroscopic study of the galaxies in these groups using GMOS on Gemini-South and FORS2 on VLT with the aim of determining if these galaxies are physically associated to the cluster. We find that three groups contain galaxies at the cluster redshift and that they are probably bound to the cluster. This is the first confirmation of filamentary structure as traced by galaxy groups at z>1. We then use several spectral features in the FORS2 spectra to determine the star formation histories of group galaxies. We find a population of relatively red star-forming galaxies in the groups that are absent from the cluster core. While similarly red star forming galaxies can also be found in the field, the average strength of the hd line is systematically weaker in group galaxies. Interestingly, these groups at z=1.2 are in an environment in which the on-going build-up of red sequence is happening. The unusual line strengths can be explained by star formation that is heavily obscured by dust. We hypothesize that galaxy-galaxy interactions, which is more efficient in the group environment, is the mechanism that drives these dust obscured star formation. The hypothesis can be tested by obtaining spectral observations in the near-IR, high resolution imaging observations and observations in the mid-IR.
We report on the spectroscopic confirmation of a huge cosmic structure around the CL0016 cluster at z=0.55. We made wide-field imaging observations of the surrounding regions of the cluster and identified more than 30 concentrations of red galaxies near the cluster redshift. The follow-up spectroscopic observations of the most prominent part of the structure confirmed 14 systems close to the cluster redshift, roughly half of which have a positive probability of being bound to the cluster dynamically. We also made an X-ray follow-up, which detected extended X-ray emissions from 70% of the systems in the X-ray surveyed region. The observed structure is among the richest ever observed in the distant Universe. It will be an ideal site for quantifying environmental variations in the galaxy properties and effects of large-scale structure on galaxy evolution.
The coagulation of dust aggregates occurs in various astrophysical
environments. Each one is characterized by different conditions that influence
the growth, e.g. relative velocities, composition, and size of the smallest
constituents (monomers). Here we study the microphysics of collisions of dust
aggregates in a four-dimensional parameter space. The parameters are the
collision energy, the initial compactness of agglomerates, the mass ratio of
collision partners, and the impact parameter. For this purpose we employ a
state of the art molecular dynamics type of model that has been extensively and
successfully tested against laboratory experiments. It simulates the motion of
individual monomers interacting dynamically via van der Waals surface forces.
The structure of aggregates is quantified by the filling factor that provides
information about the internal structure, the packing density of monomers, and
the projected surface area of aggregates. Our results show the importance of
the impact parameter that causes formation of elongated particles, due to
tensile forces acting in offset collisions. We also describe in detail the
internal structure of the resulting aggregates.
Our findings are summarized in the form of a simple collision recipe. The
recipe specifies the outcome of a collision, averaged over the impact
parameter. It is provided in tabular form for a range of physical parameters
such as impact energy and pre-collision filling factor. The dependence on the
mass ratio of impactor and target is taken into account by providing both a
local and a global branch of the recipe.
We report the redshift of a distant, highly obscured submm galaxy (SMG), based entirely on the detection of its CO line emission. We have used the newly commissioned Eight-MIxer Receiver (EMIR) at the IRAM 30m telescope, with its 8 GHz of instantaneous dual-polarization bandwidth, to search the 3-mm atmospheric window for CO emission from SMMJ14009+0252, a bright SMG detected in the SCUBA Lens Survey. A detection of the CO(3--2) line in the 3-mm window was confirmed via observations of CO(5--4) in the 2-mm window. Both lines constrain the redshift of SMMJ14009+0252 to z=2.9344, with high precision (dz=2 10^{-4}). Such observations will become routine in determining redshifts in the era of the Atacama Large Millimeter/submillimeter Array (ALMA).
Galaxies detected in the 21-cm line of neutral hydrogen (HI) from the on-going Arecibo Legacy Fast ALFA (ALFALFA) blind extragalactic HI survey have been cross-correlated with Sloan Digital Sky Survey Data Release 7 (Abazajian et al. 2009) in order to define a reference sample of HI content in regions of low galactic density. This observational sample will be used in the future to derive new standards of normal atomic gas content that allow a statistical investigation of the HI properties of galaxies in differing environments of the local universe. As a previous step, we compare here morphological indicators, like color or light concentration index, of ALFALFA detections and non-detections in low density regions. Our examination is extended also to a small data set of isolated galaxies. This kind of analysis is necessary in order to characterize as accurately as possible the type of galaxies that ALFALFA is detecting.
High-energy irradiation of the circumstellar material might impact the structure and the composition of a protoplanetary disk and hence the process of planet formation. In this paper, we present a study on the possible influence of the stellar irradiation, indicated by X-ray emission, on the crystalline structure of the circumstellar dust. The dust crystallinity is measured for 42 class II T Tauri stars in the Taurus star-forming region using a decomposition fit of the 10 micron silicate feature, measured with the Spitzer IRS instrument. Since the sample includes objects with disks of various evolutionary stages, we further confine the target selection, using the age of the objects as a selection parameter. We correlate the X-ray luminosity and the X-ray hardness of the central object with the crystalline mass fraction of the circumstellar dust and find a significant anti-correlation for 20 objects within an age range of approx. 1 to 4.5 Myr. We postulate that X-rays represent the stellar activity and consequently the energetic ions of the stellar winds which interact with the circumstellar disk. We show that the fluxes around 1 AU and ion energies of the present solar wind are sufficient to amorphize the upper layer of dust grains very efficiently, leading to an observable reduction of the crystalline mass fraction of the circumstellar, sub-micron sized dust. This effect could also erase other relations between crystallinity and disk/star parameters such as age or spectral type.
In the context of star and planet formation, understanding the formation of disks is of fundamental importance. Previous studies found that the magnetic field has a very strong impact on the collapse of a prestellar cloud, particularly in possibly suppressing the formation of a disk even for relatively modest values of the magnetic intensity. Since observations infer that cores have a substantial level of magnetization, this raises the question of how disks form. However, most studies have been restricted to the case in which the initial angle, $\alpha$, between the magnetic field and the rotation axis equals 0$^\circ$. We explore and analyse the influence of non aligned configurations on disk formation. We perform 3D ideal MHD, AMR numerical simulations for various values of $\mu$, the ratio of the mass-to-flux to the critical mass-to-flux, and various values of $\alpha$. We find that disks form more easily as $\alpha$ increases from 0 to 90$^\circ$. We propose that as the magnetized pseudo-disks become thicker with increasing $\alpha$, the magnetic braking efficiency is lowered. We also find that even small values of $\alpha$ ($\simeq$ 10-20$^\circ$) show significant differences with the alligned case. Within the framework of ideal MHD and for our choice of initial conditions, centrifugally supported disks cannot form for values of $\mu$ smaller than $\simeq$3, if the magnetic field and the rotation axis are perpendicular, and smaller than about $\simeq$5-10 when they are perfectly aligned.
Comparison of appropriate theoretical derived line ratios with observational data can yield estimates of a plasma's physical parameters, such as electron density or temperature. The usual practice in the calculation of the line ratio is the assumption of excitation by electrons/protons followed by radiative decay. Furthermore, it is normal to use the so-called coronal approximation, i.e. one only considers ionization and recombination to and from the ground state. A more accurate treatment is to include the ionization/recombination to and from meta-stable levels. Here, we apply this to two lines from adjacent ionization stages; Mg IX 368A and Mg X 625A, which has been shown to be a very useful temperature diagnostic. At densities typical of coronal hole conditions, the difference between the electron temperature derived assuming the zero density limit compared with the electron density dependent ionization/recombination is small. This however is not the case for flares where the electron density is orders of magnitude larger. The derived temperature for the coronal hole at solar maximum is around 1.04 MK compared to just below 0.82 MK at solar minimum.
LOFAR, the Low Frequency Array, is an innovative new radio telescope currently under construction in the Netherlands. With its continuous monitoring of the radio sky we expect LOFAR will detect many new transient events, including GRB afterglows and pulsating/single-burst neutron stars. We here describe all-sky surveys ranging from a time resolution of microseconds to a cadence span of years.
As a part of an ongoing study of a sample of galaxy groups showing evidence for AGN/hot gas interaction, we report on the preliminary results of an analysis of new XMM and GMRT data of the X-ray bright compact group HCG 62. This is one of the few groups known to possess very clear, small X-ray cavities in the inner region as shown by the existing Chandra image. At higher frequencies (>1.4 GHz) the cavities show minimal if any radio emission, but the radio appears clearly at lower frequencies (<610 MHz). We compare and discuss the morphology and spectral properties of the gas and of the radio source. We find that the cavities are close to pressure balance, and that the jets have a "light" hadronic content. By extracting X-ray surface brightness and temperature profiles, we also identify a shock front located around 35 kpc to the south-west of the group center.
We consider the description of the clustering of halos for physically-motivated types of non-Gaussian initial conditions. In particular we include non-Gaussianity of the type arising from single field slow-roll, multi fields, curvaton (local type), higher-order derivative-type (equilateral), vacuum-state modifications (enfolded-type) and horizon-scale GR corrections type. We show that large-scale halo bias is a very sensitive tool to probe non-Gaussianity, potentially leading, for some planned surveys, to a detection of non-Gaussianity arising from horizon-scale GR corrections.
In this paper, I review how optical spectro-interferometry has become a particularly well suited technique to study the close environment of young stars, by spatially resolving both their IR continuum and line emission regions. I summarize in which ways optical interferometers have brought major insights about our understanding of the inner part of circumstellar disks, a region in which the first stages of planet formation are thought to occur. In particular, I emphasize how new methods are now enabling to probe the hot gas emission, in addition to the circumstellar dust.
The satellite Hinode has recently revealed penumbral structures with a magnetic polarity opposite to the main sunspot polarity. They may be a direct confirmation of magnetic field lines and mass flows returning to the solar interior throughout the penumbra, a configuration previously inferred from interpretation of observed Stokes profile asymmetries. The paper points out the relationship between the reverse polarity features found by Hinode, and the model Micro-Structured Magnetic Atmospheres (MISMAs) proposed for sunspots. We show how the existing model MISMAs produce strongly redshifted reverse polarity structures as found by Hinode. Ad hoc model MISMAs also explain the asymmetric Stokes profiles observed by Hinode. The same modeling may be consistent with magnetograms of dark cored penumbral filaments if the dark cores are associated with the reverse polarity. Such hypothetical relationship will show up only in the far red wings of the spectral lines.
Dust properties appear to vary according to the environment in which the dust evolves. Previous observational indications of these variations in the FIR and submm spectral range are scarce and limited to specific regions of the sky. To determine whether these results can be generalised to larger scales, we study the evolution in dust emissivities from the FIR to mm wavelengths, in the atomic and molecular ISM, along the Galactic plane towards the outer Galaxy. We correlate the dust FIR to mm emission with the HI and CO emission. The study is carried out using the DIRBE data from 100 to 240 mic, the Archeops data from 550 mic to 2.1 mm, and the WMAP data at 3.2 mm (W band), in regions with Galactic latitude |b| < 30 deg, over the Galactic longitude range (75 deg < l < 198 deg) observed with Archeops. In all regions studied, the emissivity spectra in both the atomic and molecular phases are steeper in the FIR (beta = 2.4) than in the submm and mm (beta = 1.5). We find significant variations in the spectral shape of the dust emissivity as a function of the dust temperature in the molecular phase. Regions of similar dust temperature in the molecular and atomic gas exhibit similar emissivity spectra. Regions where the dust is significantly colder in the molecular phase show a significant increase in emissivity for the range 100 - 550 mic. This result supports the hypothesis of grain coagulation in these regions, confirming results obtained over small fractions of the sky in previous studies and allowing us to expand these results to the cold molecular environments in general of the outer MW. We note that it is the first time that these effects have been demonstrated by direct measurement of the emissivity, while previous studies were based only on thermal arguments.
We have designed and constructed a second-generation version of the Dispersed Fourier Transform Spectrograph, or dFTS. This instrument combines a spectral interferometer with a dispersive spectrograph to provide high-accuracy, high-resolution optical spectra of stellar targets. The new version, dFTS2, is based upon the design of our prototype, with several modifications to improve the system throughput and performance. We deployed dFTS2 to the Steward Observatory 2.3-meter Bok Telescope from June 2007 to June 2008, and undertook an observing program on spectroscopic binary stars, with the goal of constraining the velocity amplitude K of the binary orbits with 0.1% accuracy, a significant improvement over most of the orbits reported in the literature. We present results for radial velocity reference stars and orbit solutions for single-lined spectroscopic binaries.
In the last two decades about a dozen methods were invented which derive, from a series of composite spectra over the orbit, the spectra of individual components in binary and multiple systems. Reconstructed spectra can then be analyzed with the tools developed for single stars. Eventually this has created the opportunity for chemical composition studies in previously inaccessible components of binary stars, and to follow their chemical evolution, an important aspect in understanding evolution of stellar systems. First, we review new developments in techniques to separate and reconstruct individual spectra, and thereafter concentrate on some applications. In particular, we emphasize the elemental abundance studies for high-mass stars, and present our recent results in probing theoretical evolution models which include effects of rotationally induced mixing.
We report on the discovery of the extremely low-mass, hydrogen-rich white dwarf, NLTT 11748. Based on measurements of the effective temperature (8540+/-50 K) and surface gravity (log g = 6.20+/-0.15) obtained by fitting the observed Balmer line profiles with synthetic spectra, we derive a mass of 0.167+/-0.005 M_solar. This object is one of only a handful of white dwarfs with masses below 0.2 M_solar that are believed to be the product of close binary evolution with an episode of Roche lobe overflow onto a degenerate companion (neutron star or white dwarf). Assuming membership in the halo population, as suggested by the kinematics and adopting a cooling age of 4.0 - 6.3 Gyrs for the white dwarf, we infer a progenitor mass of 0.87 - 0.93 M_solar. The likely companion has yet to be identified, but a search for radial velocity variations may help constrain its nature.
We analyze the surface structure of the planet host star CoRoT-2a using a consistent model for both the `global' (i.e., rotationally modulated) lightcurve and the transit lightcurves, using data provided by the CoRoT mission. Selecting a time interval covering two stellar rotations and six transits of the planetary companion CoRoT-2b, we adopt a `strip' model of the surface to reproduce the photometric modulation inside and outside the transits simultaneously. Our reconstructions show that it is possible to achieve appropriate fits for the entire sub-interval using a low-resolution surface model with 36 strips. The surface reconstructions indicate that the brightness on the eclipsed section of the stellar surface is (6 +/- 1) % lower than the average brightness of the remaining surface. This result suggests a concentration of stellar activity in a band around the stellar equator similar to the behavior observed on the Sun.
We re-examine the properties of the high-velocity and extremely low mass white dwarf LP 400-22 and its close companion. Based on an extended observation timeline we determined a binary period of P= 1.01016 d, somewhat longer than the previously published period, and a mass function f(M_2)= 0.180 M_solar implying a mass for the companion M_2 > 0.41 M_solar. We also re-appraised the mass and cooling age of the white dwarf using low-metallicity (Z=0.001) evolutionary models appropriate for an old halo member, M_1 = 0.19 M_solar and t_cool~1.8 Gyr, and we infer a mass of 0.85 - 1.0 M_solar for the progenitor of the white dwarf. We discuss the likely origin of this system.
The Perseus galaxy cluster was observed by the MAGIC Cherenkov telescope for a total effective time of 24.4 hours during November and December 2008. The resulting upper limits on the gamma-ray emission above 100 GeV are in the range of 4.6 to 7.5 x 10^{-12} cm^{-2} s^{-1} for spectral indices from -1.5 to -2.5; thereby constraining the emission produced by cosmic rays, dark matter annihilations, and the central radio galaxy NGC 1275. Results are compatible with cosmological cluster simulations for the cosmic ray induced gamma-ray emission, constraining the relative cosmic ray pressure to <3.5% for the cluster core region (<7% when considering biasing effects of galaxy-sized substructures). Using simplified assumptions adopted in earlier work (constant cosmic ray-to-thermal pressure throughout the entire cluster and a power-law spectrum with an index of -2.1), we constrain the ratio of cosmic ray-to-thermal energy to E_{CR}/E_{th}<1.7%. The upper limit also translates to a level of gamma-ray emission from possible annihilations of the cluster dark matter (the dominant mass component) that is consistent with boost factors of ~10^{4} for the typically expected dark matter annihilation induced emission. Finally, the upper limits obtained for the gamma-ray emission of the central radio galaxy NGC 1275 are consistent with the recent detection by the Fermi-LAT satellite. Due to the extremely large Doppler factors required for the jet, a one-zone synchrotron self-Compton model is implausible in this case. We reproduce the observed spectral energy density by using the structured jet (spine-layer) model which has previously been adopted to explain the high-energy emission of radio galaxies.
During its early evolution, the hot, dense Universe provided a laboratory for probing fundamental physics at high energies. By studying the relics from those early epochs, such as the light elements synthesized during primordial nucleosynthesis when the Universe was only a few minutes old, and the relic, cosmic microwave photons, last scattered when the protons, alphas, and electrons (re)combined some 400 thousand years later, the evolution of the Universe may be used to test the standard models of cosmology and particle physics and to set constraints on proposals of physics beyond these standard models.
The mid- and far-IR spectral ranges are critical windows to characterize the physical and chemical processes that transform the interstellar gas and dust into stars and planets. Sources in the earliest phases of star formation and in the latest stages of stellar evolution release most of their energy at these wavelengths. Besides, the mid- and far-IR ranges provide key spectral diagnostics of the gas chemistry (water, light hydrides, organic species ...), of the prevailing physical conditions (H2, atomic fine structure lines...), and of the dust mineral and ice composition that can not be observed from ground-based telescopes. With the launch of JAXA's SPICA telescope, uninterrupted studies in the mid- and far-IR will be possible since ESA's Infrared Space Observatory (1995). In particular, SAFARI will provide full access to the 34-210um waveband through several detector arrays and flexible observing modes (from broadband photometry to medium resolution spectroscopy with R~3,000 at 63um), and reaching very high line sensitivities (~10^-19 Wm^-2, 5sigma-1hr) within a large FOV (~2'x2'). Compared to previous far-IR instruments (ISO/LWS, Akari/FIS, Spitzer/MIPS and Herschel/PACS), SAFARI will provide a superior way to obtain fully-sampled spectro-images and continuous SEDs of very faint and extended ISM sources in a wavelength domain not accessible to JWST or ALMA. The much increased sensitivity of SPICA will allow us to step forward and reveal not only the chemical complexity in the local ISM, but also in the extragalactic ISM routinely.
The physical and chemical conditions in young protoplanetary disks set the boundary conditions for planet formation. Although the dust in disks is relatively easily detected as a far-IR photometric ``excess'' over the expected photospheric emission, much less is known about the gas phase. It seems clear that an abrupt transition from massive optically thick disks (gas-rich structures where only ~1% of the total mass is in the form of dust) to tenuous debris disks almost devoid of gas occurs at ~10^7 years, by which time the majority of at least the giant planets must have formed. Indeed, these planets are largely gaseous and thus they must assemble before the gas disk dissipates. Spectroscopic studies of the disk gas content at different evolutive stages are thus critical. Far-IR water vapor lines and atomic fine structure lines from abundant gas reservoirs (e.g., [OI]63um, [SI]56um, [SiII]34um) are robust tracers of the gas in disks. Spectrometers on board Herschel will detect some of these lines toward the closest, youngest and more massive protoplanetary disks. However, according to models, Herschel will not reach the required sensitivity to (1) detect the gas residual in more evolved and tenuous transational disks that are potentially forming planets and (2) detect the gas emission from less massive protoplanetary disks around the most numerous stars in the Galaxy (M-type and cooler dwarfs). Both are unique goals for SPICA/SAFARI. Besides, SAFARI will be able to detect the far-IR modes of water ice at ~44 and ~62um, and thus allow water ice to be observed in many protoplanetary systems and fully explore its impact on planetary formation and evolution.
GX 339-4 has been one of the key sources for unravelling the accretion
ejection coupling in accreting stellar mass black holes. After a long period of
quiescence between 1999 and 2002, GX 339-4 underwent a series of 4 outbursts
that have been intensively observed by many ground based observatories [radio,
infrared(IR), optical] and satellites (X-rays). Here, we present results of
these broad-band observational campaigns, focusing on the optical-IR
(OIR)/X-ray flux correlations over the four outbursts. We found tight OIR/X-ray
correlations over four decades with the presence of a break in the IR/X-ray
correlation in the hard state. This correlation is the same for all four
outbursts. This can be interpreted in a consistent way by considering a
synchrotron self-Compton origin of the X-rays in which the break frequency
varies between the optically thick and thin regime of the jet spectrum. We also
highlight the similarities and differences between optical/X-ray and IR/X-ray
correlations which suggest a jet origin of the near-IR emission in the hard
state while the optical is more likely dominated by the blackbody emission of
the accretion disc in both hard and soft state. However we find a non
negligible contribution of 40 per cent of the jet emission in the V-band during
the hard state.
We finally concentrate on a soft-to-hard state transition during the decay of
the 2004 outburst by comparing the radio, IR, optical and hard X-rays light
curves. It appears that unusual delays between the peak of emission in the
different energy domains may provide some important constraints on jet
formation scenario.
We have obtained [Mg/Fe] for around 77% of the stars of the MILES library of stellar spectra in order to include this important information into simple stellar population (SSP) models. The abundance ratios, which were carefully calibrated to a single uniform scale, were obtained through a compilation from high spectral resolution works plus robust spectroscopic analysis at medium resolution. The high resolution data provided an extensive control sample. Average uncertainties (0.06 and 0.12 dex for the high and medium resolution samples respectively) and the good coverage of the stars with [Mg/Fe] over the MILES's parameter space will permit us to semi-empirically build up new SSP models with accurate alpha-enhancements for ages older than 1 Gyr. This will open new prospects for evolutionary stellar population synthesis.
Non-gaussianity in the microwave background radiation is bound to play a key role in giving us clues about the physics of the very early universe. However, the associated calculations, at second and even third order in perturbation theory, tend to be complicated to the point of obscuring simple underlying physical processes. In this note, we present a simple analytic procedure for approximating the non-linearity parameters f_{NL} and g_{NL} for cyclic models in which the cosmological perturbations are generated via the entropic mechanism. Our approach is quick, physically transparent and agrees well with the results of numerical calculations.
We study the stability of Einstein static universe in the Ho\v{r}ava-Lifshitz (HL) gravity with the detailed-balance condition, where the Friedmann equation gets corrected by a $1/{a^4}$ term. We find that, if the cosmological constant $\Lambda$ is negative, there exists a stable Einstein static state. The universe can stay at this stable state eternally and thus the big bang singularity can be avoided. However, in this case, it is difficult for the universe to break this stable state and then enter an inflationary era. For a positive $\Lambda$, the system has both an unstable state and a stable one. The former corresponds to an exponentially expanding phase. The universe can stay at this stable state past-eternally. Once the equation of state $w$ reaches infinity: $w\to\infty$ or $w\to-\infty$, this stable critical point coincides with the unstable one. Thus the stable state is broken and then the universe enters an inflationary era. Therefore, the big bang singularity can be avoided and a subsequent inflation can occur.
We present the first analytical inspiral-merger-ringdown gravitational waveforms from black-hole (BH) binaries with non-precessing spins. By matching a post-Newtonian description of the inspiral to a set of numerical calculations performed in full general relativity, we obtain a waveform family with a conveniently small number of physical parameters. The physical content of these waveforms includes the "orbital hang-up" effect, when BHs are spinning rapidly along the direction of the orbital angular momentum. These waveforms will allow us to detect a larger parameter space of BH binary coalescence, to explore various scientific questions related to GW astronomy, and could dramatically improve the expected detection rates of GW detectors.
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