We consider the consequences of gravitational wave recoil for unified models of active galactic nuclei (AGNs). Spatial oscillations of supermassive black holes (SMBHs) around the cores of galaxies following gravitational wave (GW) recoil imply that the SMBHs spend a significant fraction of time off-nucleus, at scales beyond that of the molecular obscuring torus. Assuming reasonable distributions of recoil velocities, we compute the off-core timescale of (intrinsically type-2) quasars. We find that roughly one-half of major mergers result in a SMBH being displaced beyond the torus for a time of 30 Myr or more, comparable to quasar activity timescales. Since major mergers are most strongly affected by GW recoil, our results imply a deficiency of type 2 quasars in comparison to Seyfert 2 galaxies. Other consequences of the recoil oscillations for the observable properties of AGNs are also discussed.
We selected a sample of 33 Gamma Ray Bursts (GRBs) detected by Swift, with known redshift and optical extinction at the host frame. For these, we constructed the de-absorbed and K-corrected X-ray and optical rest frame light curves. These are modelled as the sum of two components: emission from the forward shock due to the interaction of a fireball with the circum-burst medium and an additional component, treated in a completely phenomenological way. The latter can be identified, among other possibilities, as "late prompt" emission produced by a long lived central engine with mechanisms similar to those responsible for the production of the "standard" early prompt radiation. Apart from flares or re-brightenings, that we do not model, we find a good agreement with the data, despite of their complexity and diversity. Although based in part on a phenomenological model with a relatively large number of free parameters, we believe that our findings are a first step towards the construction of a more physical scenario. Our approach allows us to interpret the behaviour of the optical and X-ray afterglows in a coherent way, by a relatively simple scenario. Within this context it is possible to explain why sometimes no jet break is observed; why, even if a jet break is observed, it is often chromatic; why the steepening after the jet break time is often shallower than predicted. Finally, the decay slope of the late prompt emission after the shallow phase is found to be remarkably similar to the time profile expected by the accretion rate of fall-back material (i.e. proportional to t^{-5/3}), suggesting that this can be the reason why the central engine can be active for a long time.
Using the Expanded Very Large Array, we have conducted a search for 22.2 GHz H2O megamaser emission in the strongly lensed submm galaxy, SMM J16359+6612 at z=2.517. This object is lensed into three components, and after a correction for magnification is applied to its submm-wavelength flux density, it is typical of the bulk of the high-redshift, submm galaxy population responsible for the 850 um extragalactic background (S(850um)~1 mJy). We do not detect any H2O megamaser emission, but the lensing allows us to place an interesting constraint on the luminosity of any megamasers present, L(H2O) < 5305 solar luminosities for an assumed linewidth of 80 km/s. Because the far-infrared luminosity in submm galaxies is mainly powered by star formation, and very luminous H2O megamasers are more commonly associated with quasar activity, it could be that blind searches for H2O megamasers will not be an effective means of determining redshifts for less luminous members of the submm galaxy population.
We characterize spinning dust emission in the warm ionized medium by comparing templates of Galactic dust and Halpha with the 5-year maps from the Wilkinson Microwave Anisotropy Probe. The Halpha-correlated microwave emission deviates from the thermal bremsstrahlung (free-free) spectrum expected for ionized gas, exhibiting an additional broad bump peaked at ~40 GHz which provides ~20% of the peak intensity. We confirm that the bump is consistent with a modified Draine & Lazarian (1998) spinning dust model, though the peak frequency of the emission is somewhat lower than the 50 GHz previously claimed. This frequency shift results from systematic errors in the large-scale modes of the 3-year WMAP data which have been corrected in the 5-year data release. We show that the bump is not the result of errors in the Halpha template by analyzing regions of high free-free intensity, where the WMAP K-band map may be used as the free-free template. We rule out a pure free-free spectrum for the Halpha-correlated emission at high confidence: ~27sigma for the nearly full-sky fit, even after marginalizing over the CMB cross-correlation bias. We also extend the previous analysis by searching the parameter space of the Draine & Lazarian model but letting the amplitude float. The best fit for reasonable values of the characteristic electric dipole moment and density requires an amplitude factor of ~0.3. This suggests that small PAHs in the warm ionized medium are depleted by a factor of ~3.
We use a wide-field (0.9 square degree) X-ray sample with optical and GALEX ultraviolet observations to measure the contribution of Active Galactic Nuclei (AGNs) to the ionizing flux as a function of redshift. Our analysis shows that the AGN contribution to the metagalactic ionizing background peaks around z=2. The measured values of the ionizing background from the AGNs are lower than previous estimates and confirm that ionization from AGNs is insufficient to maintain the observed ionization of the intergalactic medium (IGM) at z>3. We show that only sources with broad lines in their optical spectra have detectable ionizing flux and that the ionizing flux seen in an AGN is not correlated with its X-ray color. We also use the GALEX observations of the GOODS-N region to place a 2-sigma upper limit of 0.008 on the average ionization fraction fnu(700 A)/fnu(1500 A) for 626 UV selected galaxies in the redshift range z=0.9-1.4. We then use this limit to estimate an upper bound to the galaxy contribution in the redshift range z=0-5. If the z~1.15 ionization fraction is appropriate for higher redshift galaxies, then contributions from the galaxy population are also too low to account for the IGM ionization at the highest redshifts (z>4).
We explore the use of the color-log(n) plane (where n is the global Sersic index) as a tool for subdividing the high redshift galaxy population in a physically-motivated manner. Using a series of volume-limited samples out to z=1.5 in the Hubble Ultra Deep Field (UDF) we confirm the correlation between color-log(n) plane position and visual morphology observed locally and in other high redshift studies in the color and/or structure domain. Via comparison to a low redshift sample from the Millennium Galaxy Catalogue we quantify evolution by color-log(n) type, accounting separately for the specific selection and measurement biases against each. Specifically, we measure decreases in B-band surface brightness of 1.57 +/- 0.22 mag/sq.arcsec and 1.65 +/- 0.22 mag/sq.arcsec for `blue, diffuse' and `red, compact' galaxies respectively between redshift unity and the present day.
We report on observations of GRB 080503, a short gamma-ray burst with very bright extended emission (about 30 times the gamma-ray fluence of the initial spike) in conjunction with a thorough comparison to other short Swift events. In spite of the prompt-emission brightness, however, the optical counterpart is extraordinarily faint, never exceeding 25 mag in deep observations starting at ~1 hr after the BAT trigger. The optical brightness peaks at ~1 day and then falls sharply in a manner similar to the predictions of Li & Paczynski (1998) for supernova-like emission following compact-binary mergers. However, a shallow spectral index and similar evolution in X-rays inferred from Chandra observations are more consistent with an afterglow interpretation. The extreme faintness of this probable afterglow relative to the bright gamma-ray emission argues for a very low-density medium surrounding the burst (a "naked" GRB), consistent with the lack of a coincident host galaxy down to 28.5 mag in deep HST imaging. Our observations reinforce the notion that short GRBs generally occur outside regions of active star formation, but demonstrate that in some cases the luminosity of the extended prompt emission can greatly exceed that of the short spike, which may constrain theoretical interpretation of this class of events. Because most previous BAT short bursts without observed extended emission are too faint for this signature to have been detectable even if it were present at typical level, conclusions based solely on the observed presence or absence of extended emission in the existing Swift sample are premature. (abridged)
We quantify the effects of \emph{morphological k-correction} at $1<z<2$ by comparing morphologies measured in the K and I-bands in the COSMOS area. Ks-band data have indeed the advantage of probing old stellar populations for $z<2$, enabling a determination of galaxy morphological types unaffected by recent star formation. In paper I we presented a new non-parametric method to quantify morphologies of galaxies on seeing limited images based on support vector machines. Here we use this method to classify $\sim$$50 000$ $Ks$ selected galaxies in the COSMOS area observed with WIRCam at CFHT. The obtained classification is used to investigate the redshift distributions and number counts per morphological type up to $z\sim2$ and to compare to the results obtained with HST/ACS in the I-band on the same objects from other works. We associate to every galaxy with $Ks<21.5$ and $z<2$ a probability between 0 and 1 of being late-type or early-type. The classification is found to be reliable up to $z\sim2$. The mean probability is $p\sim0.8$. It decreases with redshift and with size, especially for the early-type population but remains above $p\sim0.7$. The classification is globally in good agreement with the one obtained using HST/ACS for $z<1$. Above $z\sim1$, the I-band classification tends to find less early-type galaxies than the Ks-band one by a factor $\sim$1.5 which might be a consequence of morphological k-correction effects. We argue therefore that studies based on I-band HST/ACS classifications at $z>1$ could be underestimating the elliptical population. Using our method, we observe an increase of the early-type population from $z\sim2$ ($21.9%\pm8%$) to the present ($32.0%\pm5%$) probably reflecting a progressive building up of the red sequence from late-type objects.
Brown dwarfs and low-mass stellar companions are interesting objects to study since they occupy the mass region between deuterium and hydrogen burning. We report here the serendipitous discovery of a low-mass companion in an eccentric orbit around a solar-type main sequence star. The stellar primary, TYC 2534-698-1, is a G2V star that was monitored both spectroscopically and photometrically over the course of several months. Radial velocity observations indicate a minimum mass of 0.037 M_solar and an orbital period of ~103 days for the companion. Photometry outside of the transit window shows the star to be stable to within ~6 millimags. The semi-major axis of the orbit places the companion in the 'brown dwarf desert' and we discuss potential follow-up observations that could constrain the mass of the companion.
Overwhelming evidence has accumulated in recent years that supernova explosions are intrinsically 3-dimensional phenomena with significant departures from spherical symmetry. We review the evidence derived from spectropolarimetry that has established several key results: virtually all supernovae are significantly aspherical near maximum light; core-collapse supernovae behave differently than thermonuclear (Type Ia) supernovae; the asphericity of core-collapse supernovae is stronger in the inner layers showing that the explosion process itself is strongly aspherical; core-collapse supernovae tend to establish a preferred direction of asymmetry; the asphericity is stronger in the outer layers of thermonuclear supernovae providing constraints on the burning process. We emphasize the utility of the Q/U plane as a diagnostic tool and revisit SN 1987A and SN 1993J in a contemporary context. An axially-symmetric geometry can explain many basic features of core-collapse supernovae, but significant departures from axial symmetry are needed to explain most events. We introduce a spectropolarimetry type to classify the range of behavior observed in polarized supernovae. Understanding asymmetries in supernovae is important for phenomena as diverse as the origins of gamma-ray bursts and the cosmological applications of Type Ia supernovae in studies of the dark energy content of the universe.
(Abridged) The c2d Spitzer Legacy project obtained images and photometry with both IRAC and MIPS instruments for five large, nearby molecular clouds. This paper combines information drawn from studies of individual clouds into a combined and updated statistical analysis of star formation rates and efficiencies, numbers and lifetimes for SED classes, and clustering properties. Current star formation efficiencies range from 3% to 6%. Taken together, the five clouds are producing about 260 solar masses of stars per Myr. The star formation surface density is more than an order of magnitude larger than would be predicted from the Kennicutt relation used in extragalactic studies. Measured against the dense gas probed by the maps of dust continuum emission, the efficiencies are much higher, and the current stock of dense cores would be exhausted in 1.8 Myr on average. The derived lifetime for the Class I phase is 0.44 to 0.54 Myr, considerably longer than some estimates. Similarly, the lifetime for the Class 0 SED class, 0.10 to 0.16 Myr, is longer than early estimates. The great majority (90%) of young stars lie within loose clusters with at least 35 members and a stellar density of 1 solar mass per cubic pc. Accretion at the sound speed from an isothermal sphere over the lifetime derived for the Class I phase could build a star of about 0.25 solar masses, given an efficiency of 0.3. Our data confirm and aggravate the "luminosity problem" for protostars. Our results strongly suggest that accretion is time variable, with prolonged periods of very low accretion. Based on a very simple model and this sample of sources, half the mass of a star would be accreted during only 7% of the Class I lifetime, as represented by the eight most luminous objects.
We study afterglow flares of gamma-ray bursts (GRBs) in the framework of the late internal shock (LIS) model based on a careful description for the dynamics of a pair of shocks generated by a collision between two homogeneous shells,. First, by confronting the model with some fundamental observational features of X-ray flares, we find some constraints on the properties of the pre-collision shells that are directly determined by the central engine of GRBs. Second, high energy emission associated with X-ray flares, which arises from synchrotron self-Compton (SSC) emission of LISs, is investigated in a wide parameter space. The predicted flux of high energy flares may reach as high as $\sim 10^{-8}\rm erg cm^{-2}s^{-1}$, which is likely to be detectable with the Large Area Telescope (LAT) aboard \textit{the Fermi Space Telescope}
The LUNASKA (Lunar UHE Neutrino Astrophysics with the Square Kilometre Array) project is a theoretical and experimental project developing the lunar Cherenkov technique for the next generation of giant radio-telescope arrays. This contribution presents our simulation results on the directional dependence of the technique for UHE neutrino detection. In particular, these indicate that both the instantaneous sensitivities and time-integrated limits from lunar Cherenkov experiments such as those at Parkes, Goldstone, Kalyazin and ATCA are highly anisotropic. We study the regions of the sky which have not been probed by either these or other experiments, and present the expected sky coverage of future experiments with the SKA. Our results show how the sensitivity of Lunar Cherenkov observations to potential astrophysical sources of UHE particles may be maximised by choosing appropriate observations dates and antenna-beam pointing positions.
LUNASKA (Lunar UHE Neutrino Astrophysics with the Square Kilometre Array) is a theoretical and experimental project developing the lunar Cherenkov technique for the next generation of giant radio-telescope arrays. Here we report on a series of observations with ATCA (the Australia Telescope Compact Array). Our current observations use three of the six 22m ATCA antennas with a 600 MHz bandwidth at 1.2-1.8 GHz, analogue dedispersion filters to correct for the typical night-time ionospheric dispersion, and state-of-the-art 2 GHz FPGA-based digital pulse detection hardware. We have observed so as to maximise the UHE neutrino sensitivity in the region surrounding the galactic centre and to Centaurus A, to which current limits on the highest-energy neutrinos are relatively weak.
All available observations of photometric standard stars obtained with the Gemini Multi-Object Spectrograph at Gemini North in the period from August 2001 to December 2003 have been used to establish the calibrations for photometry obtained with the instrument. The calibrations presented in this paper are based on significantly more photometric standard star observations than usually used by the individual users. Nightly photometric zero points as well as color terms are determined. The color terms are expected to be valid for all observations taken prior to UT 2004 November 21 at which time the Gemini North primary mirror was coated with silver instead of aluminum. While the nightly zero points are accurate to 0.02 mag or better (random errors), the accuracy of the calibrations is limited by systematic errors from so-called "sky concentration", an effect seen in all focal reducer instruments. We conclude that an accuracy of 0.035 to 0.05 mag can be achieved by using calibrations derived in this paper. The color terms are strongest for very red objects, e.g. for objects with (r'-z')=3.0 the resulting z' magnitudes will be ~0.35 mag too bright if the color term is ignored. The calibrations are of importance to the large Gemini user community with data obtained prior to UT 2004 November 21, as well as future users of achive data from this period in time.
High resolution and seeing-free spectroscopic observation of a decaying
sunspot was done with the Solar Optical Telescope aboard Hinode satellite. The
target was NOAA 10944 located in the west side of the solar surface from March
2 to March 4, 2007. The umbra included many umbral dots (UDs) with size of ~300
km in continuum light. We report the magnetic structures and Doppler velocity
fields around UDs, based on the Milne-Eddington inversion of the two iron
absorption lines at 6302 angstrom.
The histograms of magnetic field strength(B), inclination angle(i), and
Doppler velocity(v) of UDs showed a center-to-limb variation. Observed at disk
center, UDs had (1)slightly smaller field strength (Delta B=-17 Gauss) and
(2)relative blue shifts (Delta v=28 m s-1) compared to their surroundings. When
the sunspot got close to the limb, UDs and their surroundings showed almost no
difference in the magnetic and Doppler values. This center-to-limb variation
can be understood by the formation height difference in a cusp-shaped
magnetized atmosphere around UDs, due to the weakly magnetized hot gas
intrusion. In addition, some UDs showed oscillatory light curves with multiple
peaks around 10 min, which may indicate the presence of the oscillatory
convection. We discuss our results in the frameworks of two theoretical models,
the monolithic model (Schussler & Vogler 2006) and the field-free intrusion
model (Spruit & Scharmer 2006).
We introduce the main lines and specificities of the CoRoT Seismology Core Programme. The development and consolidation of this programme has been made in the framework of the CoRoT Seismology Working Group. With a few illustrative examples, we show how CoRoT data will help to address various problems associated with present open questions of stellar structure and evolution.
Primordial quantum fluctuations produced by inflation are conventionally assumed to be statistically homogeneous, a consequence of translational invariance. In this paper we quantify the potentially observable effects of a small violation of translational invariance during inflation, as characterized by the presence of a preferred point, line, or plane. We explore the imprint such a violation would leave on the cosmic microwave background anisotropy, and provide explicit formulas for the expected amplitudes $<a_{lm}a_{l'm'}^*>$ of the spherical-harmonic coefficients.
South Pole ice is predicted to be the best medium for acoustic neutrino detection. Moreover, ice is the only medium in which all three dense-medium detection methods (optical, radio, and acoustic) can be used to monitor the same interaction volume. Events detected in coincidence between two methods allow significant background rejection confidence, which is necessary to study rare GZK neutrinos. In 2007 and 2008 the South Pole Acoustic Test Setup (SPATS) was installed as a research and development project associated with the IceCube experiment. The purpose of SPATS is to measure the acoustic ice properties at the South Pole in order to determine the feasibility of a future large hybrid array. The deployment and performance of SPATS are described, as are first results and work in progress on the sound speed, background noise, and attenuation.
We discuss whether the process of winding-up the magnetic field by
differential rotation in a new-born quark-star can cause an energy emission
rate high enough and lasting sufficiently long to explain long gamma ray
bursts. Within the magneto-hydrodynamics, we study the torsional oscillations
and the extraction of energy from a new-born, hot, differentially rotating
quark-star.
The new-born compact star is a fast rotator which blows a relativistic
leptonic wind. The star's torsional oscillation considerably modulates this
wind emission when it is odd and of a sufficient amplitude, which is relatively
easy to reach. Odd oscillations may occur just after the formation of a
quark-star.Other asymmetries can cause similar effects. The buoyancy of
wound-up magnetic fields is inhibited, or its effects are limited, by a variety
of different mechanisms described in the paper. Direct electromagnetic emission
by the torsional oscillation in an outside vacuum or in the leptonic wind
surrounding the compact object is found to be insignificant.
On the contrary, the twist given to the outer magnetic field by an odd
torsional oscillation is generally sufficient to break the star's magnetosphere
open. The Poynting emission of the star in its leptonic environment is then
radiated from all its surface and is considerably enhanced during these open
episodes, tapping at the bulk rotational energy of the star. This results in
intense energy shedding in the first tens of minutes after the collapse for
magnetized quark-stars with an initial poloidal field of order of 10**14 Gauss,
sufficient to explain long gamma-ray bursts.
Ethyl cyanide is an abundant molecule in hot molecular clouds. Lines from 13C isotopically substituted ethyl cyanide were identified in Orion. To enable the search and the possible detection of other isotopologues of ethyl cyanide in interstellar objects, we have studied the rotational spectrum of deuterated ethyl cyanide: CH2DCH2CN (in-plane and out-of-plane) and CH3CHDCN and the spectrum of15N substituted ethyl cyanide CH3CH2C15N. The rotational spectrum of each species in the ground state was measured in the microwave and millimeter-submillimeter wavelength range using a waveguide Fourier transform spectrometer (8 - 17 GHz) and a source-modulated spectrometer employing backward-wave oscillators (BWOs) (150 - 260 and 580 - 660 GHz). From the fitting procedure, accurate spectroscopic constants were derived for each of the species. These new sets of spectroscopic constants enable us to predict reliably the rotational spectrum (lines frequencies and intensities) in the 4-1000 GHz frequency range and for J and Ka up to 80 and 31, respectively. Combined with IRAM 30 m antenna observations of Orion, this experimental study allowed us to detect 15N substituted ethyl cyanide for the first time in Orion. The derived column density and rotational temperature are 10^13 cm-2 and 150 K for the plateau and 3 10^14 cm-2 and 300 K for the hot core. The deuterated species were searched for but were not detected. The upper limit to the column density of each deuterated isotopologues was 10^14 cm-2.
To study the acoustic properties of the Antarctic ice the South Pole Acoustic Test Setup (SPATS) was installed in the upper part of drill holes for the IceCube neutrino observatory. An important parameter for the design of a future acoustic neutrino telescope is the acoustic background noise in the ice and its spatial and temporal variations. We study the absolute noise level depth profile from SPATS data and discuss systematic uncertainties. The measured noise is very stable over one year of data taking, and we estimate the absolute noise level to be < 10 mPa in the frequency range from 10 kHz to 50 kHz at depths below 200 m. This noise level is of the same order of magnitude as observed by ocean based acoustic neutrino detection projects in good weather conditions.
The light distribution in the disks of many galaxies is non-axisymmetric or `lopsided' with a spatial extent much larger along one half of a galaxy than the other, as in M101. Recent near-IR observations show that lopsidedness is common. The stellar disks in nearly 30 % of galaxies have significant lopsidedness, greater than 10 % measured as the Fourier amplitude of the m=1 component normalized to the average value. This asymmetry is traced particularly well by the atomic hydrogen gas distribution lying in the outer parts. The lopsidedness also occurs in the nuclear regions, where the nucleus is offset with respect to the outer isophotes. The galaxies in a group environment show higher lopsidedness. The origin of lopsidedness could be due to the disk response to a tidally distorted halo, or via gas accretion. The lopsidedness has a large impact on the dynamics of the galaxy, its evolution, the star formation in it, and on the growth of the central black hole and on the nuclear fueling, merging of binary black holes etc. The disk lopsidedness can be used as a diagnostic to study the halo asymmetry. This is an emerging area in galactic structure and dynamics. In this review, the observations to measure the lopsided distribution, as well as the theoretical progress made so far to understand its origin and properties, and the related open problems will be discussed. (abridged).
A hydro-acoustic imaging system was tested in a pilot study on distant localization of elements of the Baikal underwater neutrino telescope. For this innovative approach, based on broad band acoustic echo signals and strictly avoiding any active acoustic elements on the telescope, the imaging system was temporarily installed just below the ice surface, while the telescope stayed in its standard position at 1100 m depth. The system comprised an antenna with four acoustic projectors positioned at the corners of a 50 meter square; acoustic pulses were "linear sweep-spread signals" - multiple-modulated wide-band signals (10-22 kHz) of 51.2 s duration. Three large objects (two string buoys and the central electronics module) were localized by the 3D acoustic imaging, with a accuracy of ~0.2 m (along the beam) and ~1.0 m (transverse). We discuss signal forms and parameters necessary for improved 3D acoustic imaging of the telescope, and suggest a layout of a possible stationary bottom based 3D imaging setup. The presented technique may be of interest for neutrino telescopes of km3-scale and beyond, as a flexible temporary or as a stationary tool to localize basic telescope elements, while these are completely passive.
We review the status of the Lake Baikal Neutrino Experiment. The Neutrino Telescope NT200 has been operating since 1998 and has been upgraded to the 10 Mton detector NT200+ in 2005. We present selected astroparticle physics results from long-term operation of NT200. Also discussed are activities towards acoustic detection of UHE-energy neutrinos, and results of associated science activities. Preparation towards a km3-scale (Gigaton volume) detector in Lake Baikal is currently a central activity. As an important milestone, a km3-prototype string, based on completely new technology, has been installed and is operating together with NT200+ since April, 2008.
A prototype string for the future km3-scale Baikal neutrino telescope has been deployed in April, 2008 and is fully integrated into the NT200+ telescope. All basic string elements - optical modules (with 12"/13" hemispherical photomultipliers), 200MHz FADC readout and calibration system - have been redesigned following experience with NT200+. First results of in-situ operation of this prototype string are presented.
The South Pole Acoustic Test Setup (SPATS) is located in the upper part of the optical neutrino observatory IceCube, currently under construction. SPATS consists of four strings at depths between 80 m and 500 m below the surface of the ice with seven stages per string. Each stage is equipped with an acoustic sensor and a transmitter. Three strings (string A-C) were deployed in the austral summer 2006/07. SPATS was extended by a fourth string (string D) with second generation sensors and transmitters in 2007/08. One second generation sensor type HADES (Hydrophone for Acoustic Detection at South Pole) consists of a ring-shaped piezo-electric element coated with polyurethane. The development of the sensor, optimization of acoustic transmission by acoustic impedance matching and first in-situ results will be discussed.
We present CAIXA, a Catalogue of AGN In the XMM-Newton Archive. It consists of all the radio-quiet X-ray unobscured ($\mathrm{N_H}<2\times10^{22}$ cm$^{-2}$) Active Galactic Nuclei (AGN) observed by XMM-Newton in targeted observations, whose data are public as of March 2007. With its 156 sources, this is the largest catalogue of high signal-to-noise X-ray spectra of AGN. All the EPIC pn spectra of the sources in CAIXA were extracted homogeneously and a baseline model was applied in order to derive their basic X-ray properties. These data are complemented by multiwavelength data found in the literature: Black Hole masses, Full Width Half Maximum (FWHM) of H$\beta$, radio and optical fluxes. Here we describe our homogeneous spectral analysis of the X-ray data in CAIXA and present all the results on the parameters adopted in our best-fit models.
We report on the results of INTEGRAL observations of the neutron star low mass X-ray binary SAX J1810.8-2609 during its latest active phase in August 2007. The current outburst is the first one since 1998 and the derived luminosity is 1.1-2.6x10^36 erg s-1 in the 20-100 keV energy range. This low outburst luminosity and the long-term time-average accretion rate of ~5x10^-12Msolar/yr suggest that SAXJ 1810.8-2609 is a faint soft X-ray transient. During the flux increase, spectra are consistent with a thermal Comptonization model with a temperature plasma of ~23-30 keV and an optical depth of ~1.2-1.5, independent from luminosity of the system. This is a typical low hard spectral state for which the X-ray emission is attributed to the upscattering of soft seed photons by a hot, optically thin electron plasma. During the decay, spectra have a different shape, the high energy tail being compatible with a single power law. This confirm similar behavior observed by BeppoSAX during the previous outburst, with absence of visible cutoff in the hard X-ray spectrum. INTEGRAL/JEM-X instrument observed four X-ray bursts in Fall 2007. The first one has the highest peak flux (~3.5Crab in 3--25 keV) giving an upper limit to the distance of the source of about 5.7 kpc, for a LEdd~3.8x10^38 erg s^-1. The observed recurrence time of ~1.2 days and the ratio of the total energy emitted in the persistent flux to that emitted in the bursts (~73) allow us to conclude that the burst fuel was composed by mixed hydrogen and helium with X>0.4.
Aims: We investigate the formation of flux ropes in a flux emergence region
and their rise into the outer atmosphere of the Sun.
Methods: We perform 3D numerical experiments solving the time-dependent and
resistive MHD equations.
Results: A sub-photospheric twisted flux tube rises from the solar interior
and expands into the corona. A flux rope is formed within the expanding field,
due to shearing and reconnection of field lines at low atmospheric heights. If
the tube emerges into a non-magnetized atmosphere, the flux rope rises, but
remains confined inside the expanding magnetized volume. On the contrary, if
the expanding tube is allowed to reconnect with a preexisting coronal field,
the flux rope experiences a full eruption with a rise profile which is in
qualitative agreement with erupting filaments and Coronal Mass Ejections.
This work intends to provide a brief summary of some of the Galactic science issues for the next generation of very high energy (VHE) instruments. The latter is here generically understood, as an instrument or set of instruments providing about one order of magnitude more sensitivity at its central energy (at about 1 TeV), but extending the observational window to have a real broadband capability (from a few tens of GeV up to tens of TeV); exceeding at low energies the current VHE threshold for observations set by MAGIC as well as the few-tens-of-GeV sensitivity set by Fermi. Science topics regarding populations of emitters, pulsars and their nebula, binaries, supernova remnants, stars, and their associations, are discussed.
Several types of variable stars are found along the HR diagram whose pulsations are driven by the $\kappa$-mechanism. Given their nature, the precise ($T_{\rm eff}-L$) domain where these pulsators are located is highly dependent on the value of opacity and on its variation inside the star. We analyze the sensitivity of opacity driven pulsators of spectral-type A and B ($\delta$ Scuti, $\beta$ Cephei and SPB stars) to the opacity tables (OP/OPAL) and to the chemical composition of the stellar matter. We also briefly discuss the effect of opacity on pulsators whose oscillations are not driven by the $\kappa$-mechanism, such as $\gamma$ Doradus and solar-like stars.
(Abridged) We present numerical simulations of the spectral evolution and radio emission of superluminal components in relativistic jets. We have developed an algorithm (SPEV) for the transport of a population of non-thermal particles (NTPs). For very large values of the ratio of gas pressure to magnetic field energy density ($\sim 6\times 10^4$), quiescent over-pressured jet models show substantial spectral evolution compared to models whithout radiative losses. Larger values of the magnetic field yield much shorter jets. Larger magnetic fields result in shorter losses-dominated regimes, with a rapid and intense radiation of energy. We also show that jets with a positive photon spectral index may result if the lower limit $\gamma_min$ of the NTP energy distribution is placed close or above a threshold $\gamma_M$, where the synchrotron function R has its maximum. A temporary increase of the Lorentz factor at the jet inlet produces a traveling perturbation that appears in the synthetic maps as a radio component moving downstream at superluminal apparent speed. Here we show that trailing components can be originated through multiple physical mechanisms. They can also be produced in over-pressured jets, where the existence of recollimation shocks does not allow for a direct identification of such features as Kelvin-Helmholtz modes. The observational imprint of trailing components depends on the observing frequency. If the magnetic field is large, the spectral index in the rarefaction trailing the traveling perturbation does not change much with respect to the same model without any hydrodynamic perturbation. If the synchrotron losses are considered the spectral index displays a smaller value than in the corresponding region of the quiescent jet model.
Context. The primary energy release in solar flares is almost certainly due to magnetic reconnection, making this a strong candidate as a mechanism for particle acceleration. While particle acceleration in 2D geometries has been widely studied, investigations in 3D are a recent development. Two main classes of reconnection regimes at a 3D magnetic null point have been identified: fan and spine reconnection Aims. Here we investigate particle trajectories and acceleration during reconnection at a 3D null point, using a test particle numerical code, and compare the efficiency of the fan and spine regimes in generating an energetic particle population. Methods. We calculated the time evolution of the energy spectra. We discuss the geometry of particle escape from the two configurations and characterise the trapped and escaped populations. Results. We find that fan reconnection is less efficent than spine reconnection in providing seed particles to the region of strong electric field where acceleration is possible. The establishment of a steady-state spectrum requires approximately double the time in fan reconnection. The steady-state energy spectrum at intermediate energies (protons 1 keV to 0.1 MeV) is comparable in the fan and spine regimes. While in spine reconnection particle escape takes place in two symmetric jets along the spine, in fan reconnection no jets are produced and particles escape in the fan plane, in a ribbon-like structure.
We investigate the ability of both LTE and Non-LTE models to fit the near UV band absolute flux distribution and individual spectral line profiles of three standard stars for which high quality spectrophotometry and high resolution spectroscopy are available: The Sun (G2 V), Arcturus (K2 III), and Procyon (F5 IV-V). We investigate 1) the effect of the choice of atomic line list on the ability of NLTE models to fit the near UV band flux level, 2) the amount of a hypothesized continuous thermal absorption extinction source required to allow NLTE models to fit the observations, and 3) the semi-empirical temperature structure required to fit the observations with NLTE models and standard continuous near UV extinction. We find that all models that are computed with high quality atomic line lists predict too much flux in the near UV band for Arcturus, but fit the warmer stars well. The variance among independent measurements of the solar irradiance in the near UV is sufficiently large that we cannot definitely conclude that models predict too much near UV flux, in contrast to other recent results. We surmise that the inadequacy of current atmospheric models of K giants in the near UV band is best addressed by hypothesizing that there is still missing continuous thermal extinction, and that the missing near UV extinction becomes more important with decreasing effective temperature for spectral classes later than early G, suggesting a molecular origin.
In a series of papers, we developed a technique for estimating the inner eccentricity in hierarchical triple systems, with the inner orbit being initially circular. However, for certain combinations of the masses and the orbital elements, the secular part of the solution failed. In the present paper, we derive a new solution for the secular part of the inner eccentricity, which corrects the previous weakness. The derivation applies to hierarchical triple systems with coplanar and initially circular orbits. The new formula is tested numerically by integrating the full equations of motion for systems with mass ratios from 10^(-3) to 10^(3). We also present more numerical results for short term eccentricity evolution, in order to get a better picture of the behaviour of the inner eccentricity.
We present the Space-based multi-band astronomical Variable Objects Monitor
mission (SVOM) decided by the Chinese National Space Agency (CNSA) and the
French Space Agency (CNES). The mission which is designed to detect about 80
Gamma-Ray Bursts (GRBs) of all known types per year, will carry a very
innovative scientific payload combining a gamma-ray coded mask imagers
sensitive in the range 4 keV to 250 keV, a soft X-ray telescope operating
between 0.5 to 2 keV, a gamma-ray spectro-photometer sensitive in the range 50
keV to 5 MeV, and an optical telescope able to measure the GRB afterglow
emission down to a magnitude limit M$_R=23$ with a 300 s exposure. A particular
attention will be also paid to the follow-up in making easy the observation of
the SVOM detected GRB by the largest ground based telescopes.
Scheduled for a launch in 2013, it will provide fast and reliable GRB
positions, will measure the broadband spectral energy distribution and temporal
properties of the prompt emission, and will quickly identify the optical
afterglows of detected GRBs, including those at very high redshift.
The Auger Collaboration reports that the arrival directions of >~60 EeV ultra-high energy cosmic rays (UHECRs) cluster along the supergalactic plane and correlate with active galactic nuclei (AGN) within ~ 100 Mpc. The association of several events with the nearby radio galaxy Centaurus A supports the paradigm that UHECRs are powered by supermassive black-hole engines and accelerated to ultra-high energies in the shocks formed by variable plasma winds in the inner jets of radio galaxies. The GZK horizon length of 60 EeV UHECR protons is ~ 100 Mpc, consistent with a largely proton composition of the UHECRs. In this scenario, the sources of UHECRs are FR II radio galaxies and FR I galaxies like Cen A with scattered radiation fields that enhance UHECR neutral-beam production. Radio galaxies with jets pointed away from us can still be observed as UHECR sources due to deflection of UHECRs by magnetic fields in the radio lobes of these galaxies. A broadband ~ MeV -- 10 EeV radiation component in the spectra of blazar AGN is formed by UHECR-induced cascade radiation in the extragalactic background light. This emission is too faint to be seen from Cen A, but could be detected from more luminous blazars.
We present low resolution (R approximately 250) spectroscopy in the near-IR (0.8 to 2.5um) of the EXor variables. These are the initial results (obtained during the period 2007-2008) from a long term photometric and spectroscopic program aimed to study the variability in the accretion processes of pre-Main Sequence (PMS) stars, by correlating the continuum fluctuations with the spectroscopical properties. Eight sources have been observed in different epochs, for a total of 25 acquired spectra. EXor spectra show a wide variety of emission features dominated by HI recombination (Paschen and Brackett series). We have investigated whether line and continuum variability could be due to a variable extinction, but such hypothesis is applicable only to the peculiar source PV Cep. By comparing the observed spectra with a wind model, mass loss rates in the range (2-10)x10^(-8) M_sun} yr^(-1) are derived, along with other wind parameters. Consistent results are also obtained by assuming that HI lines are due to accretion. CO overtone is also detected in the majority of the sources both in absorption and in emission. It appears to come from regions more compact than winds, likely the stellar photosphere (when in absorption) and the circumstellar disk (when in emission). NaI and CaI IR lines behave as the CO does, thus they are thought to arise in the same locations. For some targets multiple spectra correspond to different activity stages of the source. Those exhibiting the largest continuum variation at 2um (DeltaK > 1 mag) present a significant line flux fading during the continuum declining phases. In particular, CO absorption (emission) appears associated to inactive (active) stages, respectively.
In the last decade we have seen an enormous increase in the size and quality of spectroscopic galaxy surveys, both at low and high redshift. New statistical techniques to analyse large portions of galaxy spectra are now finding favour over traditional index based methods. Here we will review a new robust and iterative Principal Component Analysis (PCA) algorithm, which solves several common issues with classic PCA. Application to the 4000AA break region of galaxies in the VIMOS VLT Deep Survey (VVDS) and Sloan Digital Sky Survey (SDSS) gives new high signal-to-noise ratio spectral indices easily interpretable in terms of recent star formation history. In particular, we identify a sample of post-starburst galaxies at z~0.7 and z~0.07. We quantify for the first time the importance of post-starburst galaxies, consistent with being descendants of gas-rich major mergers, for building the red sequence. Finally, we present a comparison with new low and high redshift "mock spectroscopic surveys" derived from a Millennium Run semi-analytic model.
Previous work has shown the Orion Bar to be an interface between ionized and molecular gas, viewed roughly edge on, which is excited by the light from the Trapezium cluster. Much of the emission from any star-forming region will originate from such interfaces, so the Bar serves as a foundation test of any emission model. Here we combine X-ray, optical, IR and radio data sets to derive emission spectra along the transition from H+ to H0 to H2 regions. We then reproduce the spectra of these layers with a simulation that simultaneously accounts for the detailed microphysics of the gas, the grains, and molecules, especially H2 and CO. The magnetic field, observed to be the dominant pressure in another region of the Orion Nebula, is treated as a free parameter, along with the density of cosmic rays. Our model successfully accounts for the optical, IR and radio observations across the Bar by including a significant magnetic pressure and also heating by an excess density of cosmic rays, which we suggest is due to cosmic rays being trapped in the compressed magnetic field. In the Orion Bar, as we had previously found in M17, momentum carried by radiation and winds from the newly formed stars pushes back and compresses the surrounding gas. There is a rough balance between outward momentum in starlight and the total pressure in atomic and molecular gas surrounding the H+ region. If the gas starts out with a weak magnetic field, the starlight from a newly formed cluster will push back the gas and compress the gas, magnetic field, and cosmic rays until magnetic pressure becomes an important factor.
The physics of the solar chromosphere depends in a crucial way on its magnetic structure. However there are presently very few direct magnetic field diagnostics available for this region. Here we investigate the diagnostic potential of the Hanle effect on the Ba II D2 line resonance polarization for the determination of weak chromospheric turbulent magnetic fields......
We show that, due to the high optical depth of the intergalactic medium to Lyman-alpha photons before the Epoch of Reionization, the Lyman-alpha scattering rate responsible for the Wouthuysen-Field effect from an isolated source will be negligible unless (1) there is sufficient time for the scattering photons to establish a steady state, or (2) the scattering gas is undergoing internal expansion or has a peculiar motion of tens to hundreds of km/s away from the source. We present steady-state solutions in the radiative diffusion approximation for the radiation field trapped in a clump of gas and show that this may result in an enhancement, by a factor of up to 10^6, of the strength of the Wouthuysen-Field effect over that obtained from the free-streaming limit. Solutions to the time-dependent diffusion equation, however, suggest that the timescales required to reach such a steady state will generally exceed the source lifetimes. In the presence of internal expansion, a steady state may be established as photons are redshifted into the red wing, and significant enhancement in the scattering rate may again be produced. Alternatively, a substantial scattering rate may arise in systems with a peculiar motion away from the source that redshifts the received radiation into the resonance line centre. As a consequence, at epochs z<30, when collisional decoupling is small except in dense regions, and prior to the establishment of any large-scale diffuse radiation field of resonance line photons, the 21cm signature from the Intergalactic Medium produced by the Wouthuysen-Field effect will in general trace the peculiar velocity field of the gas in addition to its density structure.
We have performed shell-model calculations of the half-lives and neutron-branching probabilities of the r-process waiting point nuclei at the magic neutron number N=82. These new calculations use a larger model space than previous shell model studies and an improved residual interaction which is adjusted to recent spectroscopic data around A=130. Our shell-model results give a good account of all experimentally known half-lives and $Q_\beta$-values for the N=82 r-process waiting point nuclei. Our half-life predictions for the N=82 nuclei with Z=42--46 agree well with recent estimates based in the energy-density functional method.
A snapshot is presented of the present status of our knowledge of the TeV gamma-ray universe. Emphasis is put on observations made using the imaging atmospheric Cherenkov technique. The capabilities of the present generation of telescopes is listed. Progress has been dramatic and several features have been different from what was anticipated. The catalog of sources includes some 78 objects and these are tabulated as extragalactic sources (24), supernovae remnants (11), pulsar wind nebulae (10), binaries (4), miscellaneous (9), diffuse high energy sources (3) and unidentified sources (20). Some comments are made on the factors influencing the past and future development of the field.
We present a Bayesian approach to modelling galaxy clusters using multi-frequency pointed observations from telescopes that exploit the Sunyaev--Zel'dovich effect. We use the recently developed MultiNest technique (Feroz, Hobson & Bridges, 2008) to explore the high-dimensional parameter spaces and also to calculate the Bayesian evidence. This permits robust parameter estimation as well as model comparison. Tests on simulated Arcminute Microkelvin Imager observations of a cluster, in the presence of primary CMB signal, radio point sources (detected as well as an unresolved background) and receiver noise, show that our algorithm is able to analyse jointly the data from six frequency channels, sample the posterior space of the model and calculate the Bayesian evidence very efficiently on a single processor. We also illustrate the robustness of our detection process by applying it to a field with radio sources and primordial CMB but no cluster, and show that indeed no cluster is identified. The extension of our methodology to the detection and modelling of multiple clusters in multi-frequency SZ survey data will be described in a future work.
We present extensive photometry at ultraviolet (UV), optical, and near-infrared (NIR) wavelengths, as well as dense sampling of optical spectra, for the normal type Ia supernova (SN Ia) 2005cf. From the well-sampled light curves, we find that SN 2005cf reached a B-band maximum at 13.63+/-0.02 mag, with an observed luminosity decline rate dm_15(B) = 1.05+/-0.03 mag. The correlations between the decline rate and various color indexes, recalibrated on the basis of an expanded SN Ia sample, yielded E(B-V)_host=0.09+/-0.03 mag for SN2005cf. The UV photometry was obtained with the HST and the Swift Ultraviolet/Optical Telescope, and the results match each other to within 0.1-0.2 mag. The UV light curves show similar evolution to the broadband U, with an exception in the 2000-2500 Angstrom spectral range (corresponding to the F220W/uvm2 filters), where the light curve appears broader and much fainter than that on either side (likely owing to the intrinsic spectral evolution). Combining the UV data with the ground-based optical and NIR data, we establish the generic UV-optical-NIR bolometric light curve for SN 2005cf and derive the bolometric corrections in the absence of UV and/or NIR data. The overall spectral evolution of SN 2005cf is similar to that of a normal SN Ia, but with variety in the strength and profile of the main feature lines. The spectra at early times displayed strong, detached high-velocity (HV) features in the Ca II H&K doublet and NIR triplet. Similar HV features may exist in the SiII 6355 absorption line which evolved rapidly from a flat-bottomed feature in the earliest phase to a triangular shape one week before maximum, and may be common in other normal SNe Ia. The possible origin of the HV absorption features is briefly discussed (abridged).
We consider the possibility of realizing inflation in nonlocal field theories containing infinitely many derivatives. Such constructions arise naturally in string field theory and also in a number of toy models, such as the p-adic string. After reviewing the complications (ghosts and instabilities) that arise when working with high derivative theories we discuss the initial value problem and perturbative stability of theories with infinitely many derivatives. Next, we examine the inflationary dynamics and phenomenology of such theories. Nonlocal inflation can proceed even when the potential is naively too steep and generically predicts large nongaussianity in the Cosmic Microwave Background.
In this work, we find exact wormhole solutions in the context of noncommutative geometry, and further explore their physical properties and characteristics. The energy density of these wormhole geometries is a smeared and particle-like gravitational source, where the mass is diffused throughout a region of linear dimension $\sqrt{\alpha}$ due to the intrinsic uncertainty encoded in the coordinate commutator. Furthermore, we also analyze these wormhole geometries considering that the equation governing quantum fluctuations behaves as a backreaction equation. In particular, the energy density of the graviton one loop contribution to a classical energy in a traversable wormhole background and the finite one loop energy density is considered as a self-consistent source for these wormhole geometries. Interesting solutions are found for an appropriate range of the parameters, validating the perturbative computation introduced in this semi-classical approach.
A Faraday rotation experiment can set limits on the magnetic moment of a electrically-neutral, dark-matter particle, and the limits increase in stringency as the candidate-particle mass decreases. Consequently, if we assume the dark-matter particle to be a thermal relic, our most stringent constraints emerge at the keV mass scale. We discuss how such an experiment could be realized and determine the limits on the magnetic moment as a function of mass which follow given demonstrated experimental capacities.
The LISA Parameter Estimation (LISAPE) Taskforce was formed in September 2007 to provide the LISA Project with vetted codes, source distribution models, and results related to parameter estimation. The Taskforce's goal is to be able to quickly calculate the impact of any mission design changes on LISA's science capabilities, based on reasonable estimates of the distribution of astrophysical sources in the universe. This paper describes our Taskforce's work on massive black-hole binaries (MBHBs). Given present uncertainties in the formation history of MBHBs, we adopt four different population models, based on (i) whether the initial black-hole seeds are small or large, and (ii) whether accretion is efficient or inefficient at spinning up the holes. We compare four largely independent codes for calculating LISA's parameter-estimation capabilities. All codes are based on the Fisher-matrix approximation, but in the past they used somewhat different signal models, source parametrizations and noise curves. We show that once these differences are removed, the four codes give results in extremely close agreement with each other. Using a code that includes both spin precession and higher harmonics in the gravitational-wave signal, we carry out Monte Carlo simulations and determine the number of events that can be detected and accurately localized in our four population models.
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A number of recent works in astronomy and cosmology have relied upon theoretical He I emissivities, but we know of no effort to quantify the uncertainties in the atomic data. We analyze and assign uncertainties to all relevant atomic data, perform Monte Carlo analyses, and report standard deviations in the line emissivities. We consider two sets of errors, which we call "optimistic" and "pessimistic." We also consider three different conditions, corresponding to prototypical Galactic and extragalactic H II regions and the epoch of cosmological recombination. In the extragalactic H II case, the errors we obtain are comparable to or larger than the errors in some recent $Y_p$ calculations, including those derived from CMB observations. We demonstrate a systematic effect on primordial abundance calculations; this effect cannot be reduced by observing a large number of objects. In the cosmological recombination case, the errors are comparable to many of the effects considered in recent calculations.
We present results from {\it Chandra} observations of the galaxy pair NGC 7619 and NGC 7626, the two dominant members of the Pegasus group. The X-ray images show a brightness edge associated with each galaxy, which we identify as merger cold fronts. The edges are sharp, and the axes of symmetry of the edges are roughly anti-parallel, suggesting that these galaxies are falling towards one another in the plane of the sky. The detection of merger cold fronts implies a merging subgroup scenario, since the alternative is that the galaxies are falling into a pre-existing $\sim1$ keV halo without a dominant galaxy of its own, and such objects are not observed. We estimate the 3D velocities from the cold fronts and show that the velocity vectors are indeed most likely close to the plane of the sky, with a relative velocity of $\sim1190\kms$. The relative velocity is consistent with what is expected from the infall of two roughly equal mass subgroups whose total viral mass equals that of the Pegasus group. We conclude that the Pegasus cluster is currently forming from a major merger of two subgroups, dominated by NGC 7619 and NGC 7626. NGC 7626 contains a strong radio source, a core with two symmetric jets and radio lobes. Although we find no associated structure in the X-ray surface brightness map, the temperature map reveals a clump of cool gas just outside the southern lobe, presumably entrained by the lobe, and an extension of cooler gas into the lobe itself. The jet axis is parallel with the projected direction of motion of NGC 7626 (inferred from the symmetry axis of the merger cold front), and the southern leading jet is foreshortened as compared to the northern trailing one, possibly due to the additional ram pressure the forward jet encounters.
We employ a high-resolution LCDM N-body simulation to present merger rate predictions for dark matter halos and investigate how common merger-related observables for galaxies--such as close pair counts, starburst counts, and the morphologically disturbed fraction--likely scale with luminosity, stellar mass, merger mass ratio, and redshift from z=0 to z=4. We provide a simple 'universal' fitting formula that describes our derived merger rates for dark matter halos a function of dark halo mass, merger mass ratio, and redshift, and go on to predict galaxy merger rates using number density-matching to associate halos with galaxies. For example, we find that the instantaneous merger rate of m/M>0.3 mass ratio events into typical L > f L* galaxies follows the simple relation dN/dt=0.03(1+f)(1+z)^2.1 Gyr^-1. Despite the rapid increase in merger rate with redshift, only a small fraction of >0.4 L* high-redshift galaxies (~3% at z=2) should have experienced a major merger (m/M >0.3) in the very recent past (t< 100 Myr). This suggests that short-lived, merger-induced bursts of star formation should not contribute significantly to the global star formation rate at early times, in agreement with observational indications. We emphasize that great care must be made in comparisons to observations because the predicted observables depend very sensitively on galaxy luminosity, redshift, overall mass ratio, and uncertain relaxation timescales for merger remnants. We show that the majority of bright galaxies at z=3 should have undergone a major merger (>0.3) in the last 700 Myr and conclude that mergers almost certainly play an important role in delivering baryons and influencing the kinematic properties of Lyman Break Galaxies (LBGs). (abridged)
Using results from structural analysis of a sample of nearly 1000 local galaxies from the Sloan Digital Sky Survey, we estimate how the mass in central black holes is distributed amongst elliptical galaxies, classical bulges and pseudo-bulges, and investigate the relation between their stellar masses and central stellar velocity dispersion sigma. Assuming a single relation between elliptical galaxy/bulge mass, M_Bulge, and central black hole mass, M_BH, we find that 55 per cent of the mass in black holes in the local universe is in the centres of elliptical galaxies, 41 per cent in classical bulges and 4 per cent in pseudo-bulges. We find that ellipticals, classical bulges and pseudo-bulges follow different relations between their stellar masses and sigma, and the most significant offset occurs for pseudo-bulges in barred galaxies. This structural dissimilarity leads to discrepant black hole masses if single M_BH-M_Bulge and M_BH-sigma relations are used. Adopting relations from the literature, we find that the M_BH-sigma relation yields an estimate of the total mass density in black holes that is 70 per cent larger than if the M_BH-M_Bulge relation is used.
Photometry results of 32 asteroids are reported from only seven observing nights on only seven fields, consisting of 34.11 cumulative hours of observations. The data were obtained with a wide-field CCD (40.5'x27.3') mounted on a small, 46-cm telescope at the Wise Observatory. The fields are located within 1.5 degrees from the ecliptic plane and include a region within the main asteroid belt. The observed fields show a projected density of ~23.7 asteroids per square degree to the limit of our observations. 13 of the lightcurves were successfully analyzed to derive the asteroids' spin periods. These range from 2.37 up to 20.2 hours with a median value of 3.7 hours. 11 of these objects have diameters in order of two km and less, a size range that until recently has not been photometrically studied. The results obtained during this short observing run emphasize the efficiency of wide-field CCD photometry of asteroids, which is necessary to improve spin statistics and understand spin evolution processes. We added our derived spin periods to data from the literature and compared the spin rate distributions of small main belt asteroids (5>D>0.15 km) with that of bigger asteroids and of similar-sized NEAs. We found that the small MBAs do not show the clear Maxwellian-shaped distribution as large asteroids do; rather they have a spin rate distribution similar to that of NEAs. This implies that non-Maxwellian spin rate distribution is controlled by the asteroids' sizes rather than their locations.
We present narrow and broad K-band observations of the Class 0/I source IRAS 18148-0440 that span 17 years. The infrared nebula associated with this protostar in the L483 dark cloud is both morphologically and photometrically variable on a time scale of only a few months. This nebula appears to be an infrared analogue to other well-known optically visible variable nebulae associated with young stars, such as Hubble's Variable Nebula. Along with Cepheus A, this is one of the first large variable nebulae to be found that is only visible in the infrared. The variability of this nebula is most likely due to changing illumination of the cloud rather than any motion of the structure in the nebula. Both morphological and photometric changes are observed on a time scale only a few times longer than the light crossing time of the nebula, suggesting very rapid intrinsic changes in the illumination of the nebula. Our narrow-band observations also found that H_2 knots are found nearly twice as far to the east of the source as to its west, and that H_2 emission extends farther east of the source than the previously known CO outflow.
The detection in 10 bursts of an optical counterpart emission (i.e. during the prompt GRB phase) that is 10-10000 brighter than the extrapolation of the burst spectrum to optical frequencies suggests a synchrotron self-Compton origin for the GRB emission, synchrotron producing the optical counterpart emission. In this model, the second upscattering of the burst photons yields a prompt GeV-TeV emission, whose brightness depends strongly on an unknown quantity, the peak energy of the primary synchrotron spectrum. Measurements of the optical, gamma-ray, and GeV prompt fluxes can be used to test the synchrotron self-Compton model for GRBs and to determine directly the total radiative output of GRBs. For a set of 29 GRBs with optical counterpart detections, we find that the expected GeV photon flux should correlate with the fluence of the sub-MeV emission and should anticorrelate with the brightness of the optical counterpart, the strength of these correlations decreasing for an increasing width of the synchrotron peak energy distribution. The detection of a GeV prompt emission consistent with the extrapolation of the burst spectrum to higher energies would rule out the synchrotron self-Compton model if the sub-MeV burst emission were very bright and the (intrinsic) optical counterpart were very dim.
Coronal magnetic field may be characterized by how its field lines
interconnect regions of opposing photospheric flux -- its connectivity.
Connectivity can be quantified as the net flux connecting pairs of opposing
regions, once such regions are identified. One existing algorithm will
partition a typical active region into a number of unipolar regions ranging
from a few dozen to a few hundred, depending on algorithmic parameters. This
work explores how the properties of the partitions depend on some algorithmic
parameters, and how connectivity depends on the coarseness of partitioning for
one particular active region magnetogram. We find the number of connections
among them scales with the number of regions even as the number of possible
connections scales with its square.
There are several methods of generating a coronal field, even a potential
field. The field may be computed inside conducting boundaries or over an
infinite half-space. For computation of connectivity, the unipolar regions may
be replaced by point sources or the exact magnetogram may be used as a lower
boundary condition. Our investigation shows that the connectivities from these
various fields differ only slightly -- no more than 15%. The greatest
difference is between fields within conducting walls and those in the
half-space. Their connectivities grow more different as finer partitioning
creates more source regions. This also gives a quantitative means of
establishing how far away conducting boundaries must be placed in order not to
significantly affect the extrapolation. For identical outer boundaries, the use
of point sources instead of the exact magnetogram makes a smaller difference in
connectivity: typically 6% independent of the number of source regions.
We have conducted a comprehensive mid-IR spectroscopic investigation of 67 Low Ionization Nuclear Emission Line Regions (LINERs) using archival observations from the high resolution modules of the Infrared Spectrograph on board the Spitzer Space Telescope. Using the [NeV] 14 and 24um lines as active galactic nuclei (AGN) diagnostics, we detect active black holes in 39% of the galaxies in our sample, many of which show no signs of activity in either the optical or X-ray bands. In particular, a detailed comparison of multi-wavelength diagnostics shows that optical studies fail to detect AGN in galaxies with large far-IR luminosities. These observations emphasize that the nuclear power source in a large percentage of LINERs is obscured in the optical. Indeed, the majority of LINERs show mid-IR [NeV]14/[NeV]24um flux ratios well below the theoretical low-density limit, suggesting that there is substantial extinction toward even the [NeV]-emitting region . Combining optical, X-ray, and mid-IR diagnostics, we find an AGN detection rate in LINERs of 74%, higher than previously reported statistics of the fraction of LINERs hosting AGN. The [NeV]24um /[OIV]26um mid-IR line flux ratio in "AGN-LINERs" is similar to that of standard AGN, suggesting that the spectral energy distribution (SED) of the intrinsic optical/UV continuum is similar in the two. This result is in contrast to previous suggestions of a UV deficit in the intrinsic broadband continuum emission in AGN-LINERs. Consistent with our finding of extinction to the [NeV]-emitting region, we propose that extinction may also be responsible for the observed optical/UV deficit seen in at least some AGN-LINERs.
We present results from three-dimensional, self-gravitating radiation
hydrodynamical models of gas accretion by planetary cores. In some cases, the
accretion flow is resolved down to the surface of the solid core -- the first
time such simulations have been performed. We investigate the dependence of the
gas accretion rate upon the planetary core mass, and the surface density and
opacity of the encompassing protoplanetary disc. Accretion of planetesimals is
neglected.
We find that high-mass protoplanets are surrounded by thick circumplanetary
discs during their gas accretion phase but, contrary to locally-isothermal
calculations, discs do not form around accreting protoplanets with masses ~<
50M_Earth when radiation hydrodynamical simulations are performed, even if the
grain opacity is reduced from interstellar values by a factor of 100. We find
that the opacity of the gas plays a large role in determining the accretion
rates for low-mass planetary cores. For example, reducing the opacities from
interstellar values by a factor of 100 leads to roughly an order of magnitude
increase in the accretion rates for 10-20M_Earth protoplanets. The dependence
on opacity becomes less important in determining the accretion rate for more
massive cores where gravity dominates the effects of thermal support and the
protoplanet is essentially accreting at the runaway rate. Finally, for low-mass
planetary cores (~< 20M_Earth), we obtain accretion rates that are in agreement
with previous one-dimensional quasi-static models. This indicates that
three-dimensional hydrodynamical effects may not significantly alter the gas
accretion timescales that have been obtained from quasi-static models.
We propose an algorithm for denoising the cosmic microwave background (CMB) signal induced by cosmic strings on small patches of the celestial sphere, and for mapping the underlying string network. The CMB temperature anisotropies are taken as a simple superposition of a potential non-Gaussian string signal characterized by localized temperature steps, and Gaussian noise corresponding to the standard component of the CMB induced by adiabatic perturbations. Our wavelet domain Bayesian denoising (WDBD) algorithm is based on statistical modelling of the string signal in the space of coefficients of a steerable wavelet decomposition. We show that the coefficients of the string signal exhibit sparse behaviour and for fixed string tension are well described by generalized Gaussian distributions. Assuming statistical independence of the coefficients, the Bayesian least squares estimator of the string signal contaminated with Gaussian noise can be computed by numerical integration for any particular value of the string tension. An overall estimate of the coefficients of the string signal can then be formed as an average of the corresponding estimates, weighted by the posterior probability distribution of the string tension under a power spectral model. The denoised string signal is obtained by inverting the wavelet transform and the reconstructed string network can be mapped as the magnitude of its gradient. We evaluate the denoising performance from the magnitude of gradient map on the basis of the detectability of strings by eye as a function of the string tension, as well as examining the signal-to-noise ratio, correlation coefficient, and kurtosis of that map. (abridged)
It has been argued that a Universe governed by Eddington-Born-Infeld gravity can be compatible with current cosmological constraints. The extra fields introduced in this theory can behave both as dark matter and dark energy, unifying the dark sector in one coherent framework. We show the various roles the extra fields can play in the expansion of the Universe and study the evolution of linear perturbations in the various regimes. We find that, as a unified theory of the dark sector, Eddington-Born-Infeld gravity will lead to excessive fluctuations in the Cosmic Microwave Background on large scales. In the presence of a cosmological constant, however, the extra fields can behave as a form of non-particulate dark matter and can lead to a cosmology which is entirely compatible with current observations of large scale structure. We discuss the interpretation of this form of dark matter and how it can differ from standard, particulate dark matter.
This is a contribution to be published in Meyers, Robert (Ed.) Encyclopedia of Complexity and Systems Science, Springer New York (Spring 2009).
The search for life elsewhere in the universe is a pivotal question in modern science. However, to address whether life is common in the universe we must first understand the likelihood of abiogenesis by studying the origin of life on Earth. A key missing piece is the origin of biomolecular homochirality: permeating almost every life-form on Earth is the presence of exclusively levorotary amino acids and dextrorotary sugars. In this work we discuss recent results suggesting that life's homochirality resulted from sequential chiral symmetry breaking triggered by environmental events in a mechanism referred to as punctuated chirality. Applying these arguments to other potentially life-bearing platforms has significant implications for the search for extraterrestrial life: we predict that a statistically representative sampling of extraterrestrial stereochemistry will be racemic on average.
Basic aspects of the relationship between the magnetic field and polarized maser radiation are described with the emphasis on interpreting the observed spectra. Special attention is given to three issues--the limitations on the applicability of the classic solutions of Goldreich, Keeley & Kwan (1973), inferring the strength of the magnetic field from the circular polarization when the Zeeman splitting is much less than the spectral linebreadth (especially for SiO masers), and the significance of the absence of components of the Zeeman triplet in the spectra of OH masers in regions of star formation.
We use a semi-analytic model of galaxy formation to study signatures of large-scale modulations in the star formation (SF) activity in galaxies. In order to do this we carefully define local and global estimators of the density around galaxies. The former are computed using a voronoi tessellation technique and the latter by the normalised distance to haloes and voids, in terms of the virial and void radii, respectively. As a function of local density, galaxies show a strong modulation in the SF, a result that is in agreement with those from several authors. When taking subsamples of equal local density at different large-scale environments, we find relevant global effects whereby the fraction of red galaxies diminishes for galaxies in equal local density environments farther away from clusters and closer to voids. In general, the semianalitic simulation is in good agreement with the available observational results, and offers the possibility to disentangle many of the processes responsible for the variation of galaxy properties with the environment; we find that the changes found in samples of galaxies with equal local environment but different distances to haloes or voids come from the variations in the underlying mass function of dark-matter haloes. There is an additional possible effect coming from the stellar ages, indicating that halo assembly also plays a small but significant role in shaping the properties of galaxies, and in particular, hints at a possible spatial correlation in halo/stellar mass ages.
We present the results of a combination of new stellar rotation periods and extensive information about membership in the young open clusters M35 and M34. The observations show that late-type members of both clusters divide into two distinct groups, each with a different dependence of rotation on mass (color). We discuss these new results in the context of existing rotation data for cool stars in older clusters, with a focus on the dependence of rotation on mass and age. We mention briefly tests of rotation as an "astronomical clock" (gyrochronology), and our plans to use the Kepler space mission to push observations of stellar rotation periods beyond the age of the Hyades and the Sun.
The primordial non-Gaussianity signal, if measured accurately, will allow us to distinguish between different candidate models for the cosmic inflation. Since the galaxy groups located in void regions are rare events, their mass distribution may be a sensitive probe of the primordial non-Gaussianity. We determine observationally the mass distribution of galaxy groups in void regions by analyzing the galaxy group catalog from the Sloan Digital Sky Survey DR4 and the real-space tidal field constructed from the 2Mass Survey. We also make an analytic prediction for it in the framework of the extended Press-Schechter theory, assuming non-Gaussian initial conditions. Fitting the analytic model to the observational result with the help of the Fisher analysis, we show that the primordial skewness parameter is well constrained by the mass distribution of galaxy groups in void regions.
We describe a fully three-dimensional simulation of a 1 Msun solar-type star approaching a 10^6 Msun black hole on a parabolic orbit with a pericenter distance well within the tidal radius. While falling towards the black hole, the star is not only stretched along the orbital direction but even more severely compressed at right angles to the orbit. The overbearing degree of compression achieved shortly after pericenter leads to the production of strong shocks which largely isotropize the temperature profile of the star, resulting in surface temperatures comparable to the initial temperature of the star's core. This phenomenon, which precedes the fallback accretion phase, gives rise to a unique flaring signature. We estimate that EXIST, a proposed space-based X-ray observatory, should detect at least one of these events per year.
Many early-type galaxies have been detected at wavelengths of 24 to 160 micron, but the emission is usually dominated by heating from an AGN or from the evolved stellar population. Here we present Spitzer MIPS observations of a sample of elliptical and lenticular galaxies that are rich in cold molecular gas, and we investigate whether the MIR to FIR emission could be associated with star formation activity. The 24 micron images show a rich variety of structures, including nuclear point sources, rings, disks, and smooth extended emission. Comparisons to matched-resolution CO and radio continuum images suggest that the bulk of the 24 micron emission can be traced to star formation with some notable exceptions. The 24 micron luminosities of the CO-rich galaxies are typically a factor of 15 larger than what would be expected from the dust associated with their evolved stars. In addition, FIR/radio flux density ratios are consistent with star formation. We conclude that the star formation rates in z=0 elliptical and lenticular galaxies, as inferred by other authors from UV and optical data, are roughly consistent with the molecular gas abundances and that the molecular gas is usually unstable to star formation activity.
The startling discovery of Prochter and Prochaska (2006) that the frequency of very strong (W_r(2796)>1 A) MgII absorbers along gamma-ray burst (GRB) lines of sight ([dN/dz]_{GRB} = 0.90) is more than three times the frequency along quasar lines of sight ([dN/dz]_{QSO} = 0.24), over similar redshift ranges, has yet to be understood.We reconsider the possibility that the excess of very strong MgII absorbers toward GRBs is intrinsic either to the GRBs themselves or to their immediate environment, and associated with bulk outflows with velocities as large as v_{max} ~ 0.3c. In order to examine this hypothesis, we accumulate a sample of 27 W_r(2796) > 1 A absorption systems found toward 81 quasars, and compare their properties to those of 9 W_r(2796)>1 A absorption systems found toward 6 GRBs; all systems have been observed at high spectral resolution (R = 45,000) using the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope. We make multiple comparisons of the absorber properties across the two populations, testing for differences in metallicity, ionization state, abundance patterns, dust abundance, kinematics, and phase structure. We find no significant differences between the two absorber populations using any of these metrics, implying that, if the excess absorbers toward GRB lines of sight are indeed intrinsic, they must be produced in a process which has strong similarities to the processes yielding strong MgII systems in association with intervening galaxies. Although this may seem a priori unlikely, given the high outflow velocities required for any intrinsic model, we note that the same conclusion was reached, recently, with respect to the narrow absorption line systems seen in some quasars.
We investigate the effects of magnetic fields on neutrino production in microquasars. We calculate the steady particle distributions for the pions and muons generated in p-gamma and p-p interactions in the jet taking the effects of all energy losses into account. The obtained neutrino emission is significantly modified due to the synchrotron losses suffered by secondary pions and muons. The estimates made for neutrino fluxes arriving on the Earth imply that detection of high-energy neutrinos from the vicinity of the compact object can be difficult. However, in the case of windy microquasars, the interaction of energetic protons in the jet matter of dense clumps of the wind could produce detectable neutrinos. This is because the pions and muons at larger distances from the compact object will not be affected by synchrotron losses.
Observations with the Spitzer Space Telescope have revealed a population of red-sequence galaxies with a significant excess in their 24-micron emission compared to what is expected from an old stellar population. We identify 900 red galaxies with 0.15<z<0.3 from the AGN and Galaxy Evolution Survey (AGES) selected from the NOAO Deep Wide-Field Survey Bootes field. Using Spitzer/MIPS, we classify 89 (~10%) with 24-micron infrared excess (f24>0.3 mJy). We determine the prevalence of AGN and star-formation activity in all the AGES galaxies using optical line diagnostics and mid-IR color-color criteria. Using the IRAC color-color diagram from the Spitzer Shallow Survey, we find that 64% of the 24-micron excess red galaxies are likely to have strong PAH emission features in the 8-micron IRAC band. This fraction is significantly larger than the 5% of red galaxies with f24<0.3 mJy that are estimated to have strong PAH emission, suggesting that the infrared emission is largely due to star-formation processes. Only 15% of the 24-micron excess red galaxies have optical line diagnostics characteristic of star-formation (64% are classified as AGN and 21% are unclassifiable). The difference between the optical and infrared results suggest that both AGN and star-formation activity is occurring simultaneously in many of the 24-micron excess red galaxies. These results should serve as a warning to studies that exclusively use optical line diagnostics to determine the dominant emission mechanism in the infrared and other bands. We find that ~40% of the 24-micron excess red galaxies are edge-on spiral galaxies with high optical extinctions. The remaining sources are likely to be red galaxies whose 24-micron emission comes from a combination of obscured AGN and star-formation activity.
We present the near- to mid-infared study of supernova remnants (SNRs) using the AKARI IRC Survey of the Large Magellanic Cloud (LMC). The LMC survey observed about a 10 square degree area of the LMC in five bands centered at 3, 7, 11, 15, and 24 \micron using the Infrared Camera (IRC) aboard AKARI. The number of SNRs in the survey area is 21, which is about a half of the known LMC SNRs. We systematically examined the AKARI images and identified eight SNRs with distinguishable infrared emission. All of them were detected at $\gtrsim 10$ \micron and some at 3 and 7 \micron, too. We present their AKARI images and fluxes. In the 11/15 \micron versus 15/24 \micron color-color diagram, the SNRs appear to be aligned along a modified blackbody curve, representing thermal emission from dust at temperatures between 90 and 190 K. There is a good correlation between the 24 \micron and X-ray fluxes of the SNRs. It was also found that there is a good correlation between the 24 \micron and radio fluxes even if there is no direct physical connection between them. We considered the origin of the detected mid-infrared emission in individual SNRs. We conclude that the mid-infrared emissions in five SNRs that show morphologies similar to the X-rays are dominated by thermal emission from hot dust heated by X-ray emitting plasma. Their 15/24 \micron color temperatures are generally higher than the Spitzer 24/70 \micron color temperatures, which suggests that a single-temperature dust model cannot describe the full spectral energy distribution (SED) of the SNRs. It also implies that our understanding of the full SED is essential for estimating the dust destruction rate of grains by SNR shocks.
Recently, the existence of geometrically thick dust structures in Active Galactic Nuclei (AGN) has been directly proven with the help of mid-infrared interferometry. The observations are consistent with a two-component model made up of a geometrically thin and warm central disk, surrounded by a colder, fluffy torus component. In an exploratory study, we investigate one possible physical mechanism, which could produce such a structure, namely the effect of stellar feedback from a young nuclear star cluster on the interstellar medium in centres of AGN. The model is realised with the help of the hydrodynamics code TRAMP. We follow the evolution of the interstellar medium by taking discrete mass loss and energy ejection due to stellar processes, as well as optically thin radiative cooling into account. In a post-processing step, we calculate observable quantities (spectral energy distributions and images) with the help of the radiative transfer code MC3D. The interplay between injection of mass, supernova explosions and radiative cooling leads to a two-component structure made up of a cold geometrically thin, but optically thick and very turbulent disk residing in the vicinity of the angular momentum barrier, surrounded by a filamentary structure. The latter consists of cold long radial filaments flowing towards the disk and a hot tenuous medium in between, which shows both inwards and outwards directed motions. This modelling is able to reproduce the range of observed neutral hydrogen column densities of a sample of Seyfert galaxies as well as the relation between them and the strength of the silicate 10 micron spectral feature. Despite being quite crude, our mean Seyfert galaxy model is even able to describe the SEDs of two intermediate type Seyfert galaxies observed with the Spitzer Space Telescope.
We present aperture synthesis high-resolution (~ 7'' x 3'') observations in CO(J=1-0) line, HCN(J=1-0) line, and 95 GHz continuum emission toward the central (~ 1.5 kpc) region of the nearby barred spiral galaxy M 83 with the Nobeyama Millimeter Array. Our high-resolution CO(J=1-0) mosaic map depicts the presence of molecular ridges along the leading sides of the stellar bar and nuclear twin peak structure. On the other hand, we found the distribution of the HCN(J=1-0) line emission which traces dense molecular gas (nH2 > a few x 10^4 cm^-3) shows nuclear single peak structure and coincides well with that of the 95 GHz continuum emission which traces massive starburst. The peaks of the HCN(J=1-0) line and the 95 GHz continuum emission are not spatially coincident with the optical starburst regions traced by the HST V-band image. This suggests the existence of deeply buried ongoing starburst due to strong extinction (A_v ~ 5 mag) near the peaks of the HCN(J=1-0) line and the 95 GHz continuum emission. We found that the HCN(J=1-0)/CO(J=1-0) intensity ratio R_HCN/CO correlates well with extinction-corrected SFE in the central region of M 83 at a resolution of 7.5'' (~ 160 pc). This suggests that SFE is controlled by dense gas fraction traced by R_HCN/CO even on a Giant Molecular cloud Association (GMA) scale. Moreover, the correlation between R_HCN/CO and the SFE in the central region of M 83 seems to be almost coincident with that of the Gao & Solomon (2004a) sample. This suggests that the correlation between R_HCN/CO and the SFE on a GMA (~ 160 pc) scale found in M 83 is the origin of the global correlation on a few kpc scale shown by Gao & Solomon (2004a).
A method for the asteroseismic analysis of beta Cephei stars is presented and
applied to the star nu Eridani. The method is based on the analysis of
rotational splittings, and their asymmetries using differentially-rotating
asteroseismic models. Models with masses around 7.13 M_sun, and ages around
14.9 Myr, were found to fit better 10 of the 14 observed frequencies, which
were identified as the fundamental radial mode and the three L=1 triplets g, p,
and p. The splittings and aymmetries found for these modes recover those
provided in the literature, except for p. For this last mode, all its
non-axysimmetric components are predicted by the models. Moreover, opposite
signs of the observed and predicted splitting asymmetries are found. If
identification is confirmed, this can be a very interesting source of
information about the internal rotation profile, in particular in the outer
regions of the star.
In general, the seismic models which include a description for shellular
rotation yield slightly better results as compared with those given by
uniformly-rotating models. Furthermore, we show that asymmetries are quite
dependent on the overshooting of the convective core, which make the present
technique suitable for testing the theories describing the angular momentum
redistribution and chemical mixing due to rotationally-induced turbulence.
We analyze photometric data in V and I for the globular cluster (GC) systems in five of the giant ellipticals in the Coma Cluster: NGC 4874, 4881, 4889, 4926, and IC 4051. We find that the GC luminosity functions are quite similar to one another, with a turnover derived from a composite sample of more than 9,000 GCs at V = 27.71 +- 0.07 (M_V = -7.3). Both a simple Gaussian curve and an evolved Schechter function fit the bright half of the GCLF equally well, though the Coma GCLF is broader and has a higher ``cutoff mass'' (M_c ~ 3 x 10^6 M_Sun) than in any of the Virgo giants. These five Coma members exhibit a huge range in GC specific frequency, from a low of S_N = 0.7 for NGC 4881 up to 12 for IC 4051 and NGC 4874. No single formation scenario appears able to account for these differences in otherwise-similar galaxies. The supergiant NGC 4874 has the richest globular cluster system known, probably holding more than 30,000 clusters; its true extent is not yet determined and may extend well out into the Coma potential well. For the three biggest GC systems (NGC 4874, 4889, IC 4051), all three populations are dominated by red, metal-rich clusters. Their metallicity distributions also may all have the normal bimodal form, with the two sequences at the expected mean colors <V-I>(blue) = 0.98 and <V-I>(red) = 1.15. However, the color distributions and relative numbers of metal-rich clusters show intriguing counterexamples to a trend established by Peng et al. 2008 (ApJ 681, 197) for the Virgo galaxies. At the very highest-density and most massive regimes represented by the Coma supergiants, formation of metal-rich clusters seems to have been especially favored.
We present a new measurement of the cosmic X-ray background (CXRB) in the 1.5-7 keV energy band, performed by exploiting the Swift X-ray telescope (XRT) data archive. We also present a CXRB spectral model in a wider energy band (1.5-200 keV), obtained by combining these data with the recently published Swift-BAT measurement. From the XRT archive we collect a complete sample of 126 high Galactic latitude gamma-ray burst (GRB) follow-up observations. This provides a total exposure of 7.5 Ms and a sky-coverage of 7 square degrees which represents a serendipitous survey, well suited for a direct measurement of the CXRB in the 1.5-10 keV interval. Our work is based on a complete characterization of the instrumental background and an accurate measurement of the stray-light contamination and vignetting calibration. We find that the CXRB spectrum in the 1.5-7 keV energy band can be equally well fitted by a single power-law with photon index Gamma=1.47+/-0.07 or a single power-law with photon index Gamma=1.41+/-0.06 and an exponential roll-off at 41 keV. The measured flux in the 2-10 keV energy band is 2.18+/-0.13 E-11 erg/(cm2 s deg2) in the 2-10 keV band. Combining Swift-XRT with Swift-BAT (15-200 keV) we find that, in the 1.5-200 keV band, the CXRB spectrum can be well described by two smoothly-joined power laws with the energy break at 29.0+/-0.5 keV corresponding to a nu F_nu peak located at 22.4+/-0.4 keV. Taking advantage of both the Swift high energy instruments (XRT and BAT), we produce an analytical description of the CXRB spectrum over a wide (1.5-200 keV) energy band. This model is marginally consistent with the HEAO1 measurement (~10% higher at energies higher than 20 keV, while it is significantly (30%) higher at low energies (2-10 keV).
We present the X-ray luminosity function of AGN in three energy bands (Soft: 0.5-2 keV, Hard: 2-10 keV and Ultrahard: 4.5-7.5 keV). We have used the XMS survey along with other highly complete flux-limited deeper and shallower surveys for a total of 1009, 435 and 119 sources in the Soft, Hard and Ultrahard bands, respectively. We have modeled the intrinsic absorption of the Hard and Ultrahard sources (NH function) and computed the intrinsic X-ray luminosity function in all bands using a Maximum Likelihood fit technique to an analytical model. We find that the X-ray luminosity function (XLF) is best described by a Luminosity-Dependent Density Evolution (LDDE) model. Our results show a good overall agreement with previous results in the Hard band, although with slightly weaker evolution. Our model in the Soft band present slight discrepancies with other works in this band, the shape of our present day XLF being significantly flatter. We find faster evolution in the AGN detected in the Ultrahard band than those in the Hard band. The fraction of absorbed AGN in the Hard and Ultrahard bands is dependent on the X-ray luminosity. We find evidence of evolution of this fraction with redshift in the Hard band but not in the Ultrahard band, possibly due to the low statistics. Our best-fit XLF shows that the high-luminosity AGN are fully formed earlier than the less luminous AGN. The latter sources account for the vast majority of the accretion rate and mass density of the Universe, according to an anti-hierarchical black hole growth scenario.
We present estimates of the angular power spectra of the synchrotron radiation intensity fluctuations at 6 and 20 cm for the shell type supernova remnant Cas A and the filled-centre Crab supernova remnant. We find that the intensity fluctuations of both sources have a power law power spectrum with index -3.24 +/- 0.03. This power law power spectrum is consistent with the magnetohydrodynamic turbulence in the synchrotron emitting plasma. For Cas A, there is a break in the power spectrum and the power law index changes from -3.2 to -2.2 at large angular scale. This transition occurs at an angular scale that corresponds to the shell thickness of Cas A. We interpret this as a transition from three dimensional turbulence to two dimensional turbulence on scales that are respectively smaller and larger than the shell thickness.
We present a relativistic-MHD numerical study of axisymmetric, magnetically driven jets with parameters applicable to gamma-ray burst (GRB) flows. We also present analytic expressions for the asymptotic jet shape and other flow parameters that agree very well with the numerical results. All current-carrying outflows exhibit self-collimation and consequent acceleration near the rotation axis, but unconfined outflows lose causal connectivity across the jet and therefore do not collimate or accelerate efficiently in their outer regions. Magnetically accelerated jets confined by an external pressure that varies with distance with a power-law index < 2 assume a paraboloidal shape and have an acceleration efficiency > 50%. They attain Lorentz factors > 30 on scales 10^9-3x10^10 cm, consistent with the possibility that short/hard GRB jets are accelerated on scales where they can be confined by moderately relativistic winds from accretion discs, and > 100 on scales 10^10-10^12 cm, consistent with the possibility that long/soft GRB jets are accelerated within the envelopes of collapsing massive stars. We also find that the Lorentz factor of a magnetically accelerated jet is approximately inversely proportional to the opening half-angle of the poloidal streamlines. This implies that the gamma-ray emitting components of GRB outflows are very narrow, with a half-angle < 1 degree in regions where the Lorentz factor exceeds 100, and that the afterglow light curves of these components would either exhibit a very early jet break or show no jet break at all.
Far-UV photons strongly affect the physical and chemical state of molecular gas in the vicinity of young massive stars. We have obtained maps of the HCO and H13CO+ ground state lines towards the Horsehead edge at 5'' angular resolution with a combination of IRAM PdBI and 30m observations. These maps have been complemented with IRAM-30m observations of several excited transitions at two different positions. Bright formyl radical emission delineates the illuminated edge of the nebula, with a faint emission remaining towards the shielded molecular core. Viewed from the illuminated star, the HCO emission almost coincides with the PAH and CCH emission. HCO reaches a similar abundance than HCO+ in the PDR (~1-2 x10^{-9} with respect to H2). Pure gas-phase chemistry models fail to reproduce the observed HCO abundance by ~2 orders of magnitude, except if reactions of OI with carbon radicals abundant in the PDR (i.e., CH2) play a significant role in the HCO formation. Alternatively, HCO could be produced in the PDR by non-thermal processes such as photo-processing of ice mantles and subsequent photo-desorption of either HCO or H2CO, and further gas phase photodissociation. The measured HCO/H13CO+ abundance ratio is large towards the PDR (~50), and much lower toward the gas shielded from FUV radiation (<1). We propose that high HCO abundances (>10^{-10}) together with large HCO/H13CO+ abundance ratios (>1) are sensitive diagnostics of the presence of active photochemistry induced by FUV radiation.
I suggest that the beaming factor in bright ULXs varies as $b \propto \dot m^{-2}$, where $\dot m$ is the Eddington ratio for accretion. This is required by the observed universal $L_{\rm soft} \propto T^{-4}$ relation between soft--excess luminosity and temperature, and is reasonable on general physical grounds. The beam scaling means that all observable properties of bright ULXs depend essentially only on the Eddington ratio $\dot m$, and that these systems vary mainly because the beaming is sensitive to the Eddington ratio. This suggests that bright ULXs are stellar--mass systems accreting at Eddington ratios of order 10 -- 30, with beaming factors $b \ga 0.1$. Lower--luminosity ULXs follow bolometric (not soft--excess) $L \sim T^4$ correlations and probably represent {\it sub}--Eddington accretion on to black holes with masses $\sim 10\msun$. High--mass X-ray binaries containing black holes or neutron stars and undergoing rapid thermal-- or nuclear--timescale mass transfer are excellent candidates for explaining both types. If the $b \propto \dot m^{-2}$ scaling for bright ULXs can be extrapolated to the Eddington ratios found in SS433, some objects currently identified as AGN at modest redshifts might actually be ULXs (`pseudoblazars'). This may explain cases where the active source does not coincide with the centre of the host galaxy.
The molecular cloud, DR21 Main, is an example of a large-scale gravitational collapse about an axis near the plane of the sky where the collapse is free of major disturbances due to rotation or other effects. Using flux maps, polarimetric maps, and measurements of the field inclination by comparing the line widths of ion and neutral species, we estimate the temperature, mass, magnetic field, and the turbulent kinetic, mean magnetic, and gravitational potential energies, and present a 3D model of the cloud and magnetic field.
We present a five-wave Riemann solver for the equations of ideal relativistic magnetohydrodynamics. Our solver can be regarded as a relativistic extension of the five-wave HLLD Riemann solver initially developed by Miyoshi and Kusano for the equations of ideal MHD. The solution to the Riemann problem is approximated by a five wave pattern, comprised of two outermost fast shocks, two rotational discontinuities and a contact surface in the middle. The proposed scheme is considerably more elaborate than in the classical case since the normal velocity is no longer constant across the rotational modes. Still, proper closure to the Rankine-Hugoniot jump conditions can be attained by solving a nonlinear scalar equation in the total pressure variable which, for the chosen configuration, has to be constant over the whole Riemann fan. The accuracy of the new Riemann solver is validated against one dimensional tests and multidimensional applications. It is shown that our new solver considerably improves over the popular HLL solver or the recently proposed HLLC schemes.
We consider the problem of determining the structure of the dark halo of nearby dwarf spheroidal galaxies (dSphs) from the spherical Jeans equations. Whether the dark halos are cusped or cored at the centre is an important strategic problem in modern astronomy. The observational data comprise the line-of-sight velocity dispersion of a luminous tracer population. We show that when such data are analysed to find the dark matter density with the spherical Poisson and Jeans equations, then the generic solution is a dark halo density that is cusped like an isothermal. Although milder cusps (like the Navarro-Frenk-White 1/r cusp and even cores are possible, they are not generic. Such solutions exist only if the anisotropy parameter beta and the logarithmic slope of the stellar density gamma satisfy the constraint gamma = 2 x beta at the centre or if the radial velocity dispersion falls to zero at the centre. This surprisingly strong statement is really a consequence of the assumption of spherical symmetry, and the consequent coordinate singularity at the origin. So, for example, a dSph with an exponential light profile can exist in Navarro-Frenk- White halo and have a flat velocity dispersion, but anisotropy in general drives the dark halo solution to an isothermal cusp. The identified cusp or core is therefore a consequence of the assumptions (particularly of spherical symmetry and isotropy), and not the data.
In this letter we apply dynamical system methods to study all evolutional paths admissible for all initial conditions of the FRW cosmological model with a non-minimally coupled to gravity scalar field and a barotropic fluid. We choose "energy variables" as phase variables. We reduce dynamics to a 3-dimensional dynamical system for an arbitrary potential of the scalar field in the phase space variables. After postulating the potential parameter $\Gamma$ as a function of $\lambda$ (defined as $-V'/V$) we reduce whole dynamics to a 3-dimensional dynamical system and study evolutional paths leading to current accelerating expansion. If we restrict the form of the potential then we will obtain a 2-dimensional dynamical system. We use the dynamical system approach to find a new generic quintessence scenario of approaching to the de Sitter attractor which appears only for the case of non-vanishing coupling constant.
We report the discovery of a near-infrared (nIR) counterpart to the persistent neutron-star low-mass X-ray binary 4U 1705-440, at a location consistent with its recently determined Chandra X-ray position. The nIR source is highly variable, with K_s-band magnitudes varying between 15.2 and 17.3 and additional J- and H-band observations revealing color variations. A comparison with contemporaneous X-ray monitoring observations shows that the nIR brightness correlates well with X-ray flux and X-ray spectral state. We also find possible indications for a change in the slope of the nIR/X-ray flux relation between different X-ray states. We discuss and test various proposed mechanisms for the nIR emission from neutron-star low-mass X-ray binaries and conclude that the nIR emission in 4U 1705-440 is most likely dominated by X-ray heating of the outer accretion disk and the secondary star.
The binaries known as cataclysmic variables are particular binary systems in which the primary star (a white dwarf) accretes material from a secondary via Roche-lobe mechanism. Usually, these objects have orbital period of a few hours so that a detailed temporal analysis can be performed. Here, we present Chandra ${\it XMM}$-Newton observations of a dwarf nova candidate identified in the past by optical observations towards the galactic Bulge and labeled as MACHO 104.20906.960. After a spectral analysis, we used the Lomb-Scargle technique for the period search and evaluated the confidence level using Monte-Carlo simulations. In this case, we found that the $X$-ray source shows a period of $2.03_{-0.07}^{+0.09} $ hours (3$\sigma$ error) so that it is most likely a system of interacting objects. The modulation of the signal was found with a confidence level of $>$99%. The spectrum can be described by a two thermal plasma components with X-ray flux in the 0.3--10 keV energy band of $1.77_{-0.19}^{+0.16}\times10^{-13}$ erg s$^{-1}$ cm$^{-2}$. We find that the distance of the source is approximately 1 kpc thus corresponding to a luminosity $L_{X}\simeq 2\times 10^{31}$ erg s$^{-1}$.
After a successful development of theoretical and numerical works on Fermi acceleration at relativistic shocks, some difficulties recently raised with the scattering issue, a crucial aspect of the process. Most pioneering works were developed assuming the scattering off magnetic fluctuations as given. Even in that case, when a mean field is considered, its orientation is mostly perpendicular to the shock normal in the front frame, and this tends to quench the scattering process. Solving this difficulty leads to address the issue of the generation of very intense magnetic fluctuations at short wave lengths. The relativistic motion of the shock front let the cosmic rays to visit upstream during a very short time only, making this generation of magnetic fluctuations very challenging. Anyway there is some hope to solve the problem. Thanks to a recent work by Spitkovsky (2008) \cite{AS}, we know that the process works without any mean field and now we have to investigate up to which intensity the mean field can be amplified for allowing Fermi process with appropriate fast instabilities. In this presentation, the collisionless shock structure in relativistic regime is sketched, the scattering issue is presented, and the instabilities that can provide the expected magnetic field amplification are presented as well. Although there exists observational evidence that particles are accelerated in relativistic flows and are distributed according to a power law suggesting a Fermi process, the drastic conditions for Fermi process to work are not always clearly fulfilled.
We present a catalog of 857 white dwarf (WD)-M binaries from the sixth data release (DR6) of the Sloan Digital Sky Survey (SDSS), most of which were previously identified. For 636 of them, we complete a spectral analysis and derive the basic parameters of their stellar constituents and their distances from Earth. We attempt to measure fundamental parameters of these systems by completing spectral analyses. We use a Chi^2 minimization technique to decompose each combined spectrum and derive independent parameter estimates for its components. Forty-one of the stellar duets in our spectroscopic sample are optically resolved in their respective SDSS images. For these systems, we also derive a minimum true spatial separation and a lower limit to their orbital periods, typically which are some 10^4 yr. Spectra of 167 stellar duets show significant hydrogen emission and in most cases no additional He i or He ii features. We also find that 20 of the 636 WDs are fitted to be DOs, with 16 measured to have T_eff around 40,000 K. Furthermore, we identify 70 very low-mass objects, which are secondaries of masses smaller than about 0.1 solar masses, to be candidate substellar companions. Although various selection effects may play a role, the fraction 6.4 % of WD-M star binaries with orbital separations of around 500 AU is a criterion for evolutionary models of stellar binary systems. Active M dwarfs are likely present in 155 Balmer-emitting systems, corresponding to a fraction of 24.4 %. The excess of cool DOs is most likely due to additional WDs in the DB-DO T_eff range, for which no detailed fitting was completed. The trend of the M stars being closer to Earth than the WD component is probably due to an underestimation of the theoretical M star radii.
Milagro is a water-Cherenkov detector that observes the extended air showers produced by cosmic gamma rays of energies E>100GeV. The effective area of Milagro peaks at energies E~10TeV, however it is still large even down to a few hundred GeV (~10m^2 at 100GeV). The wide field of view (~2sr) and high duty cycle (>90%) of Milagro make it ideal for continuously monitoring the overhead sky for transient Very High Energy (VHE) emissions. This study searched the Milagro data for such emissions. Even though the search was optimized primarily for detecting the emission from Gamma-Ray Bursts (GRBs), it was still sensitive to the emission from the last stages of the evaporation of Primordial Black Holes or to any other kind of phenomena that produce bursts of VHE gamma rays. Measurements of the GRB spectra by satellites up to few tens of GeV showed no signs of a cutoff. Even though multiple instruments sensitive to $GeV/TeV$ gamma rays have performed observations of GRBs, there has not yet been a definitive detection of such an emission yet. One of the reasons for that is that gamma rays with energies E>~100GeV are attenuated by interactions with the extragalactic background light or are absorbed internally at the site of the burst. There are many models that predict VHE gamma-ray emission from GRBs. A detection or a constraint of such an emission can provide useful information on the mechanism and environment of GRBs. This study performed a blind search of the Milagro data of the last five years for bursts of VHE gamma rays with durations ranging from 100musec to 316sec. No GRB localization was provided by an external instrument. Instead, the whole dataset was thoroughly searched in time, space, and duration. No significant events were detected. Upper limits were placed on the VHE emission from GRBs.
We investigate the dynamics of putative Earth-mass planets in the habitable zone (HZ) of the extrasolar planetary system OGLE-2006-BLG-109L, a close analog of the Solar System. Our work is inspired by the paper of Malhotra and Minton (2008). Using the linear Laplace--Lagrange (L--L) theory, they identified a strong secular resonance that may excite large eccentricity of orbits in the HZ. However, due to uncertain or unconstrained orbital parameters, the system of jovian planets may be found in dynamically active region of the phase space spanned by low-order mean-motion resonances. To improve the L--L model, we construct a semi-analytical averaging method in terms of the restricted problem. The mean orbits of large planets are approximated by numerically averaged osculating elements. These mean elements are used to calculate the long-term motion of terrestrial planet by means of high-order analytic secular theory developed in our previous works. The excitation of eccentricity in the HZ strongly depends on the apsidal angle of jovian configurations. For some combinations of that angle, eccentricities and semi-major axes consistent with the observations, terrestrial planets may survive in low-eccentric, long-term stable orbits in large regions of HZ. We also study the effect of post-Newtonian gravity correction on the inner secular resonance in the HZ.
We present a numerical study of the mass transfer dynamics prior to the gravitational wave-driven merger of a double white dwarf system. Recently, there has been some discussion about the dynamics of these last stages, different methods seemed to provide qualitatively different results. While earlier SPH simulations indicated a very quick disruption of the binary on roughly the orbital time scale, more recent grid-based calculations find long-lived mass transfer for many orbital periods. Here we demonstrate how sensitive the dynamics of this last stage is to the exact initial conditions. We show that, after a careful preparation of the initial conditions, the reportedly short-lived systems undergo mass transfer for many dozens of orbits. The reported numbers of orbits are resolution-biased and therefore represent only lower limits to what is realized in nature. Nevertheless, the study shows convincingly the convergence of different methods to very similar results.
We present a method to measure the relative spectral response of the Pierre Auger Observatory Fluorescence Detector. The calibration was done at wavelengths of 320, 337, 355, 380 and 405 nm using an end-to-end technique in which the response of all detector components are combined in a single measurement. A xenon flasher and notch-filters were used as the light source for the calibration device. The overall uncertainty is 4%.
We present a modified stratified jet model to interpret the observed spectral energy distributions of knots in 3C 273 jet. Based on the hypothesis of the single index of the particle energy spectrum at injection and identical emission processes among all the knots, the observed difference of spectral shape among different 3C273 knots can be understood as a manifestation of deviation of the equivalent Doppler factor of stratified emission regions in individual knot from a characteristic one. The summed spectral energy distribution of all the ten knots in 3C 273 jet can be well fitted by two components, low-energy (radio to optical) component dominated by the synchrotron radiation and high-energy component (UV, X-ray and $\gamma$-ray) dominated by the inverse Compton scattering of the cosmic microwave background. This gives a consistent spectral index of $\alpha=0.88$ ($S_\nu \propto \nu^{-\alpha}$) and a characteristic Doppler factor of 7.4. Assuming the average of the summed spectrum as the characteristic spectrum of each knot in the 3C273 jet, we further get a distribution of Doppler factor. We discuss the possible implications of these results for the physical properties in 3C 273 jet. Future GeV observations with $\it GLAST$ could separate the $\gamma$-ray emission of 3C 273 from the large scale jet and the small scale jet (i.e. the core) through measuring the GeV spectrum.
The local theory of the critical lines of 2D and 3D Gaussian fields that underline the cosmic structures is presented. In the context of cosmological matter distribution the subset of critical lines of the 3D density field serves to delineate the skeleton of the observed filamentary structure at large scales. A stiff approximation used to quantitatively describe the filamentary skeleton shows that the flux of the skeleton lines is related to the average Gaussian curvature of the 1D (2D) sections of the field, much in the same way as the density of the peaks. The distribution of the length of the critical lines with threshold is analyzed in detail, while the extended descriptors of the skeleton - its curvature and its singular points, are introduced and briefly described. Theoretical predictions are compared to measurements of the skeleton in realizations of Gaussian random fields in 2D and 3D. It is found that the stiff approximation predicts accurately the shape of the differential length, allows for analytical insight, and explicit closed form solutions. Finally, it provides a simple classification of the singular points of the critical lines: i) critical points; ii) bifurcation points; iii) slopping plateaux.
The mid-infrared spectroscopic analysis of a flux-limited sample of galaxies with fv(24um) > 10 mJy is presented. Sources observed are taken from the Spitzer First Look Survey (FLS) catalog and from the NOAO Deep Wide-Field Survey region in Bootes (NDWFS). The spectroscopic sample includes 60 of the 100 sources in these combined catalogs having fv(24um) > 10 mJy. New spectra from the Spitzer Infrared Spectrograph are presented for 25 FLS sources and for 11 Bootes AGN; these are combined with 24 Bootes starburst galaxies previously published to determine the distribution of mid-infrared spectral characteristics for the total 10 mJy sample. Sources have 0.01 < z < 2.4 and 41.8 < log vLv(15um) < 46.2 (ergs/s). Average spectra are determined as a function of luminosity; lower luminosity sources (log vLv(15um) < 44.0) are dominated by PAH features and higher luminosity sources (log vLv(15um) > 44.0) are dominated by silicate absorption or emission. We find that a rest frame equivalent width of 0.4um for the 6.2um PAH emission feature provides a well defined division between lower luminosity, "pure" starbursts and higher luminosity AGN or composite sources. Using the average spectra, fluxes fv(24um) which would be observed with the Spitzer MIPS are predicted as a function of redshift for sources with luminosities that correspond to the average spectra. AGN identical to those in this 10 mJy sample could be seen to z = 3 with fv(24um) > 1 mJy, but starbursts fall to fv(24um) < 1 mJy by z ~ 0.5. This indicates that substantial luminosity evolution of starbursts is required to explain the numerous starbursts found in other IRS results having fv(24um) > 1 mJy and z ~ 2.
We use the weighted integral form of spherical Bessel functions, and introduce a new analytical set of complete and biorthogonal potential--density basis functions. The potential and density functions of the new set have finite central values and they fall off, respectively, similar to $r^{-(1+l)}$ and $r^{-(4+l)}$ at large radii where $l$ is the latitudinal quantum number of spherical harmonics. The lowest order term associated with $l=0$ is the perfect sphere of de Zeeuw. Our basis functions are intrinsically suitable for the modeling of three dimensional, soft-centred stellar systems and they complement the basis sets of Clutton-Brock, Hernquist & Ostriker and Zhao. We test the performance of our functions by expanding the density and potential profiles of some spherical and oblate galaxy models.
The H.E.S.S. survey of the inner Galaxy in the very-high-energy gamma-ray domain has led to the discovery of many extended sources, some of which do not appear to be associated with any obvious counterpart at traditional wavelengths (radio, infrared and X-ray). In this contribution, preliminary H.E.S.S. results on one of these so-called "dark" sources, namely HESS J1503-582, are presented. After introducing the properties of this source candidate, results of the search for counterparts in several astronomical windows are shown. Finally, its possible association with a "Forbidden-Velocity-Wing", a characteristic 21 cm HI line structure that appears as a deviation from the canonical Galactic rotation curve, is discussed.
Galaxies are complex systems the evolution of which apparently results from the interplay of dynamics, star formation, chemical enrichment, and feedback from supernova explosions and supermassive black holes. The hierarchical theory of galaxy formation holds that galaxies are assembled from smaller pieces, through numerous mergers of cold dark matter. The properties of an individual galaxy should be controlled by six independent parameters including mass, angular-momentum, baryon-fraction, age and size, as well as by the accidents of its recent haphazard merger history. Here we report that a sample of galaxies that were first detected through their neutral hydrogen radio-frequency emission, and are thus free of optical selection effects, shows five independent correlations among six independent observables, despite having a wide range of properties. This implies that the structure of these galaxies must be controlled by a single parameter, although we cannot identify this parameter from our dataset. Such a degree of organisation appears to be at odds with hierarchical galaxy formation, a central tenet of the cold dark matter paradigm in cosmology.
We present a 1.5deg x 8deg (220pc x 1195pc) Multiband Imaging Photometer for Spitzer 24um image of the Galactic Center and an accompanying point source list. This image is the highest spatial resolution (6" ~ 0.25pc) and sensitivity map ever taken across the GC at this wavelength, showing the emission by warm dust in unprecedented detail. Over 120,000 point sources are identified in this catalog with signal-to-noise ratios greater than five and flux densities from 0.6mJy to 9Jy.
H.E.S.S. is currently the most sensitive instrument in the very-high-energy gamma-ray domain and has revealed many new sources along the Galactic Plane, a significant fraction of which seems to be associated with energetic pulsars. HESS J1825-137 and Vela X are considered to be the prototypes of such sources in which the large VHE nebula results from the whole history of the pulsar wind and the supernova remnant host, both evolving in a complex interstellar medium. These nebulae are seen to be offset from the pulsar position and, for HESS J1825-137, a spectral steepening at increasing distance from the pulsar has been measured. In this context, updated H.E.S.S. results on two previously published sources, namely HESS J1809-193 and HESS J1912+101, and preliminary results on the newly discovered HESS J1356-645, are presented. These extended VHE sources are thought to be associated with the energetic pulsars PSR J1809-1917, PSR J1913+1011 and PSR J1357-6429, respectively. Properties of each source in the VHE regime, together with those measured in the radio and X-ray domains, are discussed.
We report the first mid-IR detection of highly disturbed ionized gas in the ultraluminous infrared galaxy IRAS F00183-7111. The gas, traced by the 12.81um [NeII] and 15.56um [NeIII] lines, spans a velocity range of-3500 to 3000 km/s with respect to systemic velocity. Optical and near-IR spectroscopic studies show no evidence for similarly high velocity gas components in forbidden lines at shorter wavelengths. We interpret this as the result of strong extinction (Av=10-50) on the high-velocity gas, which identifies the base of the outflow traced in 5007A [OIII] as a plausible origin. Unusual excitation conditions are implied by a comparison of the mid-infrared low-excitation neon line emission and the PAH emission for a sample of 56 ULIRGs. For IRAS F00183, the neon/PAH ratio is 8 times higher than the average ratio. Similar mid-infrared kinematic and excitation characteristics are found for only 2 other ULIRGs in our sample: IRAS 12127-1412NE and IRAS 13451+1232. Both sources have an elevated neon/PAH ratio and exhibit pronounced blue wings in their 15.56um [NeIII] line profiles. IRAS 13451 even shows a strongly blue shifted and broad 14.32um [NeV] line. While for IRAS 13451 the observed [NeIII]/[NeII] and [NeV]/[NeII] line ratios indicate exposure of the blue shifted gas to direct radiation from the AGN, for IRAS F00183 and 12127 the neon line ratios are consistent with an origin in fast shocks in a high-density environment, and with an evolutionary scenario in which strongly blue shifted [Ne II] and [Ne III] emission trace the (partial) disruption of the obscuring medium around a buried AGN. The detection of strongly blue shifted [Ne V] emission in IRAS 13451 would then indicate this process to be much further advanced in this ULIRG than in IRAS F00183 and 12127, where this line is undetected.
We investigate the consequences of Birkhoff's theorem in general relativity (GR) and in Modified Newtonian dynamics (MOND). We study, in particular, the system of a finite-mass test particle inside a spherical shell. In both GR and MOND, we find non-vanishing acceleration for that test particle. The direction of the acceleration is such that it pushes the test particle toward the center of the shell. In GR, the acceleration is found analytically in the case of a small test mass with a small displacement from the center of the shell. In MOND, the acceleration is found analytically in the limit of small test mass and small displacement, and a comparison to numerical values is made. Numerical simulations are done for more general cases with parameters that mimic the system of a galaxy in a cluster. In GR, the acceleration is highly suppressed, and physically insignificant. In MOND, on the contrary, the acceleration of the point particle can be a significant fraction of the field just outside of the spherical shell.
In models with large extra dimensions, where the fundamental gravity scale can be in the electroweak range, gravitational effects in particle physics may be noticeable even at relatively low energies. In this paper, we perform simple estimates of the decays of elementary particles with a black hole intermediate state. Since black holes are believed to violate global symmetries, particle decays can violate lepton and baryon numbers. Whereas previous literature has claimed incompatibility between these rates (e.g. $p$-decay) and existing experimental bounds, we find suppressed baryon and lepton-violating rates due to a new conjecture about the nature of the virtual black holes. We assume here that black holes lighter than the (effective) Planck mass must have zero electric and color charge and zero angular momentum -- this statement is true in classical general relativity and we make the conjecture that it holds in quantum gravity as well. If true, the rates for proton-decay, neutron-antineutron oscillations, and lepton-violating rare decays are suppressed to below experimental bounds even for large extra dimensions with TeV-scale gravity. Neutron-antineutron oscillations and anomalous decays of muons, $\tau$-leptons, and $K$ and $B$-mesons open a promising possibility to observe TeV gravity effects with a minor increase of existing experimental accuracy.
The existence of a minimum length and a generalization of the Heisenberg uncertainty principle seem to be two fundamental ingredients required in any consistent theory of quantum gravity. In this letter we show that they would predict dangerous processes which are phenomenologically unacceptable. For example, long--lived virtual super--Planck mass black holes may lead to rapid proton decay. Possible solutions of this puzzle are briefly discussed.
The discrepancy on Li^7 and Li^6 abundances between the observational data and the standard Big Bang Nucleosynthesis theory prediction has been a nagging problem in astrophysics and cosmology, given the highly attractive and succesful Big Bang paradigm. One possible solution of this lithium problem is through hadronic decays of a massive metastable particle which alter the primordial element abundances. We explore this possibility using gravitino dark matter framework in which the next lightest supersymmetric particle (NLSP) is typically long-lived. We found that stop NLSP can provide an attractive solution to the lithium problem.
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We have used the VIMOS IFU to map the properties of the Seyfert 1.9 galaxy LEDA 135736. These maps reveal a number of interesting features including: an Extended Narrow Line Region detectable out to 9 kpc, an area of intense star formation located at a projected distance of 12 kpc from the centre, an elliptical companion galaxy, and kinematic features, aligned along the long-axis of the ENLR, that are consistent with radio jet-driven mass outflow. We propose that the ENLR results from extra-planar gas ionized by the AGN, and that the AGN in turn might be triggered by interaction with the companion galaxy, which can also explain the burst of star formation and morphological features. Only about two percent of the ENLR's kinetic energy is in the mass outflow. We infer from this that the bulk of mechanical energy imparted by the jet is used to heat this gas.
We present a photometric and spectroscopic study of the white dwarf population of the populous, intermediate-age open cluster M35 (NGC 2168); this study expands upon our previous study of the white dwarfs in this cluster. We spectroscopically confirm 14 white dwarfs in the field of the cluster: 12 DAs, 1 hot DQ, and 1 DB star. For each DA, we determine the white dwarf mass and cooling age, from which we derive the each star's progenitor mass. These data are then added to the empirical initial-final mass relation (IFMR), where the M35 WDs contribute significantly to the high-mass end of the relation. The resulting points are consistent with previously-published linear fits to the IFMR, modulo moderate systematics introduced by the uncertainty in the star cluster age. Based on this cluster alone, the observational lower limit on the maximum mass of white dwarf progenitors is found to be ~5.1-5.2 solar masses at the 95% confidence level; including data from other young open clusters raises this limit as high as 7.1 solar masses, depending on the cluster membership of three massive WDs and the core-composition of the most massive WDs. We find that the apparent distance modulus and extinction derived solely from the cluster white dwarfs [(m-M)v=10.45 +/- 0.08 and E(B-V)=0.185 +/- 0.010, respectively] is fully consistent with that derived from main-sequence fitting techniques. Four M35 WDs may be massive enough to have oxygen-neon cores; the assumed core composition does not significantly affect the empirical IFMR. Finally, the two non-DA WDs in M35 are photometrically consistent with cluster membership; further analysis is required to determine their memberships.
For a sample of long GRBs with known redshift, we study the distribution of the evolutionary tracks on the rest-frame luminosity-peak energy Liso-Ep' diagram. We are interested in exploring the extension of the `Yonetoku' correlation to any phase of the prompt light curve, and in verifying how the high-signal prompt duration time, Tf, in the rest frame correlates with the residuals of such correlation (Firmani et al. 2006). For our purpose, we analyse separately two samples of time-resolved spectra corresponding to 32 GRBs with peak fluxes >1.8 phot cm^-2 s^-1 from the Swift-BAT detector, and 7 bright GRBs from the CGRO-BATSE detector previously processed by Kaneko et al. (2006). After constructing the Liso-Ep' diagram, we discuss the relevance of selection effects, finding that they could affect significantly the correlation. However, we find that these effects are much less significant in the Liso x Tf-Ep' diagram, where the intrinsic scatter reduces significantly. We apply further corrections for reducing the intrinsic scatter even more. For the sub-samples of GRBs (7 from Swift and 5 from CGRO) with measured jet break time, we analyse the effects of correcting Liso by jet collimation. We find that (i) the scatter around the correlation is reduced, and (ii) this scatter is dominated by the internal scatter of the individual evolutionary tracks. These results suggest that the time, integrated `Amati' and `Ghirlanda' correlations are consequences of the time resolved features, not of selection effects, and therefore call for a physical origin. We finally remark the relevance of looking inside the nature of the evolutionary tracks.
(Abridged) We use N-body simulations to explore the effects of tidal stripping on the structure of dwarf spheroidal galaxies (dSphs). We model dSphs as King spheres embedded in NFW dark halos that orbit the Galactic potential on eccentric orbits. We find that episodes of stellar mass loss remove the initial cutoff of the bound stellar core. Once equilibrium has been re-established the outer mass profile approaches a power-law well described by a simple Plummer model. Tides also result in transient features in the outer density profile. As the system re-equilibrates, an outward-moving "excess" of stars is found at radii where the local crossing time exceeds the time elapsed since pericenter. If the orbit is known, these results provide a simple way to assess whether "breaks" and "bumps" in the profile of dSphs are actually tidal in origin. We apply this to the Sagittarius dwarf and, encouragingly, identify two features in the profile that may be traced to its two last pericentric passages. Applied to Leo I, we find that any tidal break would locate beyond the area surveyed by current data, casting doubt on recent claims of the detection of tidal debris around this galaxy. For Carina, the tidal break should occur at a radius twice farther than observed, suggesting that the outer excess of stars is not tidal in origin unless its orbit is in error. A similar comment applies to Sculptor, whose pericenter appears too large for Galactic tides to be important but whose outer profile, like that of Draco, nonetheless follows closely a Plummer-law. Fornax and Leo II show no sign of a power-law outer profile, suggesting that they have not suffered stellar tidal stripping. Published profiles for other, fainter Milky Way dSph companions do not extend sufficiently far to allow for conclusive assessment.
We present Spitzer infrared observations of the starless core L429. The IR images of this core show an absorption feature, caused by the dense core material, at wavelengths <= 70 micron. The core has a steep density profile, and reaches A_V > 35 mag near the center. We show that L429 is either collapsing or in a near-collapse state.
Most of the mass content of dark matter haloes is expected to be in the form of tidal debris. The density of debris is not constant, but rather can grow due to formation of caustics at the apocenters and pericenters of the orbit, or decay as a result of phase mixing. In the phase space, the debris assemble in a hierarchy which is truncated by the primordial temperature of dark matter. Understanding this phase structure can be of significant importance for the interpretation of many astrophysical observations and in particular dark matter detection experiments. With this purpose in mind, we develop a general theoretical framework to describe the hierarchical structure of the phase space of cold dark matter haloes. We do not make any assumption of spherical symmetry and/or smooth and continuous accretion. Instead, working with correlation functions in the action-angle space, we can fully account for the hierarchical structure (predicting a two-point correlation function ~ (\Delta J)^{-1.6} in the action space), as well as the primordial discreteness of the phase space. As an application, we estimate the boost to the dark matter annihilation signal due to the structure of the phase space within virial radius: the boost due to the hierarchical tidal debris is of order unity, whereas the primordial discreteness of the phase structure can boost the total annihilation signal by up to an order of magnitude. The latter is dominated by the regions beyond 20% of the virial radius, and is largest for the recently formed haloes with the least degree of phase mixing.
Long-duration Gamma Ray Bursts (GRBs) are linked to the collapse of massive stars and their hosts are exclusively identified as active, star forming galaxies. Four long GRBs observed at high spectral resolution at redshift 1.5 <z < 4 allowed the determination of the elemental abundances for a set of different chemical elements. In this paper, for the first time, by means of detailed chemical evolution models taking into account also dust production, we attempt to constrain the star formation history of the host galaxies of these GRBs from the study of the chemical abundances measured in their ISM. We are also able to provide constraints on the age and on the dust content of GRB hosts. Our results support the hypothesis that long duration GRBs occur preferentially in low metallicity, star forming galaxies. We compare the specific star formation rate, namely the star formation rate per unit stellar mass, predicted for the hosts of these GRBs with observational values for GRB hosts distributed across a large redshift range. Our models predict a decrease of the specific star formation rate (SSFR) with redshift, consistent with the observed decrease of the comoving cosmic SFR density between z ~2 and z=0. On the other hand, observed GRB hosts seems to follow an opposite trend in the SSFR vs redshift plot, with an increase of the SSFR with decreasing redshift. Finally, we compare the SSFR of GRB050730 host with values derived for a sample of Quasar damped Lyman alpha systems. Our results indicate that the abundance pattern and the specific star formation rates of the host galaxies of these GRBs are basically compatible with the ones determined in Quasar damped Lyman alpha systems, suggesting similar chemical evolution paths.
We present an analysis of the extreme obscuration variability observed during an XMM-Newton 5-days continuous monitoring of the AGN in NGC 1365. The source was in a reflection-dominated state in the first ~1.5 days, then a strong increase of the 7-10 keV emission was observed in ~10 hours, followed by a symmetric decrease. The spectral analysis of the different states clearly shows that this variation is due to an uncovering of the X-ray source. From this observation we estimate a size of the X-ray source D_S<10^13 cm, a distance of the obscuring clouds R~10^16 cm and a density n~10^11 cm^{-3}. These values suggest that the X-ray absorption/reflection originate from the broad line region clouds. This is also supported by the resolved width of the iron narrow Kalpha emission line, consistent with the width of the broad Hbeta line.
We study the galactic population of double compact objects (NS-NS, BH-NS, BH-BH binaries) to investigate the number (if any) of these systems that can potentially be detected with LISA at low gravitational-wave frequencies. We calculate the Galactic numbers and physical properties of these binaries and show their relative contribution from the disk, bulge and halo. It is found that, although the formation efficiency of double compact objects is very small, a few thousand of such systems should be detectable with LISA depending on the instrument low-frequency sensitivity and the efficiency of data analysis techniques for identifying highly eccentric systems. Detailed population synthesis, combined with an updated Galactic model and a realistic LISA signal simulator are used to obtain the results. We outline the prospects of the science that could be done with future LISA observations of double compact objects. And in particular, we note that LISA observations could be used to determine the fate of binaries that enter a common envelope phase while passing through Hertzsprung gap. As these binaries are the most likely progenitors of double compact objects with black holes, LISA can provide very useful limits on the evolution of massive stars.
In this paper we show that, for general scalar fields, stationary configurations are possible for shift symmetric theories only. This symmetry with respect to constant translations in field space should either be manifest in the original field variables or reveal itself after an appropriate field redefinition. In particular this result implies that neither k-Essence nor Quintessence can have exact steady state / Bondi accretion onto Black Holes. We also discuss the role of field redefinitions in k-Essence theories. Here we study the transformation properties of observables and other variables in k-Essence and emphasize which of them are covariant under field redefinitions. Finally we find that stationary field configurations are necessarily linear in Killing time, provided that shift symmetry is realized in terms of these field variables.
Recently a symmetry-based method to test for statistical isotropy of the cosmic microwave background was developed. We apply the method to template-cleaned 3-year and 5-year WMAP-$DA$ maps. We examine a wide range of angular multipoles from $2 < l < 300$. The analysis detects statistically signicant signals of anisotropy inconsistent with an isotropic CMB in some of the foreground cleaned maps. We are unable to resolve whether the anomalies have a cosmological, local astrophysical or instrumental origin. Assuming the anisotropy arises due to residual foreground contamination, we estimate the residual foreground power in the maps. For the W band maps, we also find a highly improbable degree of isotropy we cannot explain. We speculate that excess isotropy may be caused by faulty modeling of detector noise.
We present results from a spectro-interferometric study of the Miras o Cet, R Leo and W Hya obtained with the Keck Aperture Masking Experiment from 1998 Sep to 2002 Jul. The spectrally dispersed visibility data permit fitting with circularly symmetric brightness profiles such as a simple uniform disk. The stellar angular diameter obtained over up to ~ 450 spectral channels spaning the region 1.1-3.8 microns is presented. Use of a simple uniform disk brightness model facilitates comparison between epochs and with existing data and theoretical models. Strong size variations with wavelength were recorded for all stars, probing zones of H2O, CO, OH, and dust formation. Comparison with contemporaneous spectra extracted from our data show a strong anti-correlation between the observed angular diameter and flux. These variations consolidate the notion of a complex stellar atmosphere consisting of molecular shells with time-dependent densities and temperatures. Our findings are compared with existing data and pulsation models. The models were found to reproduce the functional form of the wavelength vs. angular diameter curve well, although some departures are noted in the 2.8-3.5 micron range.
Possible effects of magnetic fields in core collapse supernovae rely on an efficient amplification of the weak pre-collapse fields. The magneto-rotational instability (MRI) has been suggested to lead to rapid field growth. Although MRI studies exist for accretion discs, the application of their results to core collapse supernovae is inhibited as the physics of supernova cores is substantially different from that of accretion discs. We address the problem of growth and saturation of the MRI by means of semi-global simulations, which combine elements of global and local simulations by taking into account the presence of global background gradients and using a local computational grid. We analyze the dispersion relation of the MRI to identify different regimes of the instability. This analysis is complemented by simulations, where we consider a local computational box rotating at sub-Keplerian velocity, and where we allow for a radial entropy gradient. We identify six regimes of the MRI depending on the ratio of the entropy and angular velocity gradient. Our numerical models confirm the instability criteria and growth rates for all relevant regimes. The MRI grows exponentially within milliseconds the flow and magnetic field geometries being dominated by channel flows. The MRI growth ceases once the channels are disrupted by resistive instabilities (due to finite numerical conductivity), and MHD turbulence sets in. From an analysis of the growth rates of the resistive instabilities, we deduce scaling laws for the termination amplitude of the MRI which agree well with our numerical models. We determine the dependence of the development of coherent flow structures in the saturated state on the aspect ratio of the simulation boxes. [abbreviated]
(abridged) We use the 1.4 GHz VIMOS-VLA Deep Survey and the optical VVDS and
the CFHT-LS to compare the properties of radio loud galaxies with respect to
the whole population of optical galaxies. The availability of multiband
photometry and high quality photometric redshifts allows to derive rest frame
colors and radio luminosity functions down to a limit of a B rest-frame
magnitude of M=-20.
Galaxy properties and luminosity functions (LFs) are estimated up to z~1 for
radio loud and radio quiet early and late type galaxies. Radio loud late type
galaxies are redder than radio quiet objects of the same class and this is an
effect related to the presence of more dust in stronger star forming galaxies.
Moreover, we estimate optical LFs, stellar masses and star formation rate
distributions for radio sources and compare them with those derived for a well
defined control sample, finding that the probability for a galaxy to be a radio
emitter significantly increases at high values of these parameters. Radio loud
early type galaxies show luminosity evolution of their bivariate radio-optical
LF, due to an evolution in the radio-optical ratio. The lack of evolution of
the mass function of radio loud early type galaxies means that no new AGN are
formed at z<1. On the contrary, radio loud late type objects show a strong
evolution, both in luminosity and in density, of the radio LF for z>0.7. This
evolution is the direct effect of the strong optical evolution of this class
and no significant change with redshift of the radio-optical ratio is required.
With the knowledge of the radio-optical ratio and the optical and radio LFs for
late type galaxies, we estimated the star formation history of the Universe up
to z~1.5, using optical galaxies as tracers of the global radio emission.
The long lived afterglow emission that follows gamma-ray bursts (GRBs) was predicted prior to its detection in 1997, in the X-rays, optical and radio. It is thought to arise from the shock that is driven into the external medium as the latter decelerates the relativistic outflow that drives the GRB, and persists well after most of the energy in the outflow is transferred to the shocked external medium. As the blast wave decelerates, the typical emission frequency shifts to longer wavelength. Recent observations following the launch of the Swift satellite challenge the traditional afterglow modeling and call into questions some of the basic underlying concepts. This brief review outlines some of the major strengths and weaknesses of the standard afterglow model, as well as some of the challenges that it faces in explaining recent data, and potential directions for future study that may eventually help overcome some of the current difficulties.
For the first time, we have identified photospheric emission lines in the far-UV spectrum of a white dwarf. They were discovered in the Far Ultraviolet Spectroscopic Explorer spectrum of the hot (Teff~200,000 K) DO white dwarf KPD0005+5106 and they stem from extremely highly ionized calcium (CaX 1137, 1159 Ang). Their photospheric origin is confirmed by non-LTE line-formation calculations. This is the highest ionisation stage of any element ever observed in a stellar photosphere. Calcium has never been detected before in any hot white dwarf or central star of planetary nebula. The calcium abundance determination for KPD0005+5106 (1-10 times solar) is difficult, because the line strengths are rather sensitive to current uncertainties in the knowledge of effective temperature and surface gravity. We discuss the possibility that the calcium abundance is much lower than expected from diffusion/levitation equilibrium theory. The same emission lines are exhibited by the [WCE]-type central star NGC2371. Another CaX line pair (1461, 1504 Ang) is probably present in a Hubble Space Telescope spectrum of the PG1159-type central star NGC246.
We report the discovery of a flaring X-ray source with an optical counterpart with Halpha emission and red-excess, in the direction of the SMC. A 100 ksec X-ray observation with Chandra detected a flare lasting 6 ksec in the source CXO J005428.9-723107. The X-ray spectrum during the flare was consistent with a thermal plasma of temperature kT=2.5 keV. In quiescence following the flare the spectrum was softer (kT= 0.4 keV). Timing analysis did not reveal any significant periodicities or QPOs. Optical images taken with the Magellan-Baade 6.5m telescope show a single star in the (0.9") error circle. This star has apparent magnitude V=19.17, exhibits enhanced Halpha emission (Halpha - r = -0.88), and has a large proper motion. Alternative explanations are explored, leading to identification as a relatively nearby (Galactic) coronally active star of the BY Draconis class.
Some T Tauri stars show a peculiar X-ray spectrum that can be modelled by two components with different absorbing column densities. We seek to explain the soft X-ray component in DG Tau, the best studied of these sources, with an outflow model, taking observations at other wavelengths into consideration. We constrain the outflow properties through spectral fitting and employ simple semi-analytical formulae to describe properties of a shock wave that heats up the X-ray emitting region. The X-ray emission is consistent with its arising from the fastest and innermost component of the optically detected outflow. Only a small fraction of the total mass loss is required for this X-ray emitting component. Our favoured model requires shock velocities between 400 and 500 km/s. For a density >10^5 /cm^3 all dimensions of the shock cooling zone are only a few AU, so even in optical observations this cannot be resolved. This X-ray emission mechanism in outflows may also operate in other, less absorbed T Tauri stars, in addition to corona and accretion spots.
We imaged the protostars of the nearby region NGC1333 IRAS 4 in the water
maser line at 22.2 GHz by using the VLBA in phase referencing at milliarcsecond
scale over four epochs spaced by one month to measure proper motions. We
measure the absolute positions and proper motions of the H2O spots to
investigate the kinematics of the region from where the jet is launched.
Two protostars (A2 and B) have been detected in a highly variable H2O maser
emission, with an active phase shorter than four weeks. A 70 AU chain of
several maser spots, very well aligned, has been observed close to the B
protostar. The apparent proper motions have been derived, finding that the H2O
spots are moving along the N-NW direction with projected velocities between 10
and 50 km/s. We conclude that in IRAS 4B, water maser trace a highly collimated
bipolar jet clearly associated with the protostar.
IceTop is a 1 km^2 air shower detector presently under construction as a part
of the IceCube Observatory at South Pole. It will consist of 80 detector
stations, each equipped with two ice Cherenkov tanks, which cover 1 km^2. In
2008, the detector is half completed. One of the design goals of the detector
is to investigate cosmic rays in the energy range from the knee up to
approaching 1 EeV and study the mass composition of primary cosmic rays.
In this report the performance of IceTop, the shower reconstruction
algorithms and first results, obtained with one month of data with an array of
26 stations operated in 2007, will be presented. Preliminary results are shown
for the cosmic ray energy spectrum in the range of 1 to 80 PeV. Being located
at an atmospheric depth of only 700 g/cm^2 at the South Pole, a high
sensitivity of the zenith angle distribution to the mass composition is
observed.
The main advantage of IceTop, compared to other detectors in this energy
range, is the possibility to measure highly energetic muons from air showers in
coincidence with the IceCube detector. The muon rate at a given air shower
energy is sensitive to mass composition. The prospects of this method and
alternative methods to scrutinise different composition models will be
presented.
We describe methods used to validate data from the Y.T. Lee Array for Microwave Background Anisotropy (AMiBA), an interferometric array designed to measure the Sunyaev-Zel'dovich effect and the anisotropy of the Cosmic Microwave Background (CMB). We perform several statistical tests on data from pointed galaxy cluster observations taken in 2007 and noise data from long-term blank sky observations and measurements with the feeds covered by the absorbers. We apply power spectrum analysis, cross power spectrum analysis among different outputs with different time lags in our analog correlator, and sample variance law tests to noise data. We find that (1) there is no time variation of electronic offsets on the time scale of our two-patch observations (~10 minutes); (2) noise is correlated by less than 10% between different lags; and (3) the variance of noise scales with the inverse of time. To test the Gaussianity of the data, we apply Kolmogorov-Smirnov (K-S) tests to cluster data, and find that a 5% significance level efficiently detects data sets with known hardware problems without rejecting an excess of acceptable data. We also calculate third- and fourth-order moments and cumulants for the noise residual visibilities and find that about 95% of our data are within the 99% confidence regions of Gaussianity.
We present a fast, arbitrarily accurate method to simulate the effect of gravitational lensing of the Cosmic Microwave Background anisotropies and polarization fields by large scale structures. We demonstrate the efficiency and accuracy of the method and exhibit their dependence on the algorithm parameters.
We report upper limits to the very high energy flux (E>100 GeV) of the flat spectrum radio quasar 3C454.3 (z=0.859) derived by the Cherenkov telescope MAGIC during the high states of July/August and November/December 2007. We compare the upper limits derived in both time slots with the available quasi-simultaneous MeV-GeV data from the AGILE gamma-ray satellite and interpret the observational results in the context of leptonic emission models. The source was observed with the MAGIC telescope during the active phases of July-August 2007 and November-December 2007 and the data were analyzed with the MAGIC standard analysis tools. For the periods around the ends of July and November, characterized by the most complete multifrequency coverage, we constructed the spectral energy distributions using our data together with nearly simultaneous multifrequency (optical, UV, X-ray and GeV) data. Only upper limits can be derived from the MAGIC data. The upper limits, once corrected for the expected absorption by the extragalactic background light, together with nearly simultaneous multifrequency data, allow us to constrain the spectral energy distribution of 3C454.3. The data are consistent with the model expectations based on the inverse Compton scattering of the ambient photons from the broad line region by relativistic electrons, which robustly predicts a sharp cut-off above 20-30 GeV.
- Context: The triple stellar system delta Vel system presents a significant infrared excess, whose origin is still being debated. A large infrared bow shock has been discovered using Spitzer/MIPS observations. Although it appears as a significant contributor to the measured IR excess, the possibility exists that a circumstellar IR excess is present around the stars of the system. - Aims: The objective of the present VISIR and NACO observations is to identify whether one of the stars of the delta Vel system presents a circumstellar photometric excess in the thermal IR domain and to quantify it. - Methods: We observed delta Vel using the imaging modes of the ESO/VLT instruments VISIR (in BURST mode) and NACO to resolve the A-B system (0.6" separation) and obtain the photometry of each star. We also obtained one NACO photometry epoch precisely at the primary (annular) eclipse of delta Vel Aa by Ab. - Results: Our photometric measurements with NACO (2.17 mic), complemented by the existing visible photometry allowed us to reconstruct the spectral energy distribution of the three stars. We then compared the VISIR photometry (8.6-12.8 mic) to the expected photospheric emission from the three stars at the corresponding wavelengths. - Conclusions: We can exclude the presence of a circumstellar thermal infrared excess around delta Vel A or B down to a few percent level. This supports the conclusions of Gaspar et al. (2008) that the IR excess of delta Vel has an interstellar origin, although a cold circumstellar disk could still be present. In addition, we derive the spectral types of the three stars Aa, Ab, and B (respectively A2IV, A4V and F8V), and we estimate the age of the system around 400-500 Myr.
We have performed smoothed particle hydrodynamics (SPH) simulations to study the response of the central kiloparsec region of a gaseous disk to the imposition of nonaxisymmetric bar potentials. The model galaxies are composed of the three axisymmetric components (halo, disk, and bulge) and a non-axisymmetric bar. These components are assumed to be invariant in time in the frame corotating with the bar. The potential of spherical $\gamma$-models of Dehnen is adopted for the bulge component whose density varies as $r^{-\gamma}$ near the center and $r^{-4}$ at larger radiiand hence, possesses a central density core for $\gamma = 0$ and cusps for $\gamma > 0$. Since the central mass concentration of the model galaxies increases with the cusp parameter $\gamma$, we have examined here the effect of the central mass concentration by varying the cusp parameter $\gamma$ on the mechanism responsible for the formation of the symmetric two-armed nuclear spirals in barred galaxies. Our simulations show that the symmetric two-armed nuclear spirals are formed by hydrodynamic spiral shocks driven by the gravitational torque of the bar for the models with $\gamma = 0$ and 0.5. On the other hand, the symmetric two-armed nuclear spirals in the models with $\gamma=1$ and 1.5 are explained by gas density waves. Thus, we conclude that the mechanism responsible for the formation of the symmetric two-armed nuclear spirals in barred galaxies changes from the hydrodynamic shocks to the gas density waves when the central mass concentration increases from $\gamma = 0$ to 1.5.
We present some of the strategies being developed to classify and parameterize objects obtained with spectra from the Sloan Digital Sky Survey (SDSS) and the RAdial Velocity Experiment (RAVE) and present some results. We estimate stellar atmospheric parameters (effective temperature, gravity, and metallicity) from spectral and photometric data and use these to analyse Galactic populations. We demonstrate this through the selection of a sample of candidate Blue Horizontal-Branch and RR Lyrae stars selected from SDSS/SEGUE.
We present preliminary results on a global study of X-ray binaries using 14 Ms of data from the Rossi X-ray Timing Explorer satellite. Our initial study on GX 339-4 is recapped as an introduction to the methods used. We use a consistent analysis scheme for all objects, with three different spectral models to fit the powerlaw and disc components. We also take into account the possibility of a line being present in the data. The resulting almost 4000 observations allow the tracking of the spectral properties of the binaries as they evolve through an outburst. Our investigations concentrate on the disc and line properties of the binaries when in outburst. We also show the Disc-Fraction Luminosity diagram for the population of X-ray binaries studied which will enable us to further links with AGN.
Sunspot activity is highly variable and challenging to forecast. Yet forecasts are important, since peak activity has profound effects on major geophysical phenomena including space weather (satellite drag, telecommunications outages) and has even been correlated speculatively with changes in global weather patterns. This paper investigates trends in sunspot activity, using new techniques for decadal-scale prediction of the present solar cycle (cycle 24). First, Hurst exponent $H$ analysis is used to investigate the autocorrelation structure of the putative dynamics; then the Sugihara-May algorithm is used to predict the ascension time and the maximum intensity of the current sunspot cycle. Here we report $H$ = 0.86 for the complete sunspot number dataset (1700-2007) and $H$ = 0.88 for the reliable sunspot data set (1848-2007). Using the Sugihara-May algorithm analysis, we forecast that cycle 24 will reach its maximum in December 2012 at approximately 87 sunspots units.
We present spectropolarimetric analysis of umbral dots and a light bridge fragment that show dark lanes in G-band images. Umbral dots show upflow as well as associated positive Stokes V area asymmetry in their central parts. Larger umbral dots show down flow patches in their surrounding parts that are associated with negative Stokes V area asymmetry. Umbral dots show weaker magnetic field in central part and higher magnetic field in peripheral area. Umbral fine structures are much better visible in total circularly polarized light than in continuum intensity. Umbral dots show a temperature deficit above dark lanes. The magnetic field inclination show a cusp structure above umbral dots and a light bridge fragment. We compare our observational findings with 3D magnetohydrodynamic simulations.
The main properties of AGN are reviewed, focussing on the accretion process and on the question of whether AGN are the best factories of ultra high energy particles and photons. I recall the large differences between the accretion/ejection flows in strong and weak accretors, and I conclude that, since low luminosity AGN and even "dormant" massive black holes in nuclei of galaxies are powering strong confined magnetized jets able to accelerate high energy particles, and are present in a large proportion of galaxies, they might be better potential sources of high energy particles and photons than luminous AGN and powerful radio galaxies.
Twenty eclipsing binaries were selected for an analysis from a huge database of observations made by the INTEGRAL/OMC camera. The photometric data were processed and analyzed, resulting in a first light-curve study of these neglected eclipsing binaries. Most of the selected systems are the detached ones. The system ET Vel was discovered to be an eccentric one. Due to missing spectroscopic study of these stars, further detailed analyses are still needed.
Spitzer Space Telescope spectra reveal 10 micron silicate emission from circumstellar dust orbiting six externally-polluted white dwarfs. Micron-size glasses with an olivine stoichiometry can account for the distinctively broad wings that extend to 12 microns; these particles likely are produced by tidal-disruption of asteroids. The absence of infrared PAH features is consistent with a scenario where extrasolar rocky planets are assembled from carbon-poor solids.
We used the m-averaged spectrum technique ("collapsogram") to extract the low-frequency solar p-mode parameters of low- and intermediate-angular degrees (l \leq 35) in long time series of GONG and MDI observations. Rotational splittings and central frequencies have been measured down to ~850\muHz, including predicted modes which have not been measured previously. Both GONG and MDI frequency splitting data sets were numerically inverted to extract the internal solar rotation rate. The impact of the very low-frequency observables and the differences between GONG and MDI data sets on the inversion results are also analyzed.
We study statistically 197 long gamma-ray bursts, detected and measured in detail by the BATSE instrument of the Compton Gamma-Ray Observatory. In the sample 10 variables, describing for any burst the time behavior of the spectra and other quantities, are collected. The factor analysis method is used to find the latent random variables describing the temporal and spectral properties of GRBs. The application of this particular method to this sample indicates that five factors and the $\REpk$ spectral variable (the ratio of peak energies in the spectrum) describe the sample satisfactorily. Both the pseudo-redshifts inferred from the variability, and the Amati-relation in its original form, are disfavored.
We describe Chandra/ACIS-I observations of the massive ~ 13--14 Myr-old cluster, h Persei, part of the famous Double Cluster (h and chi Persei) in Perseus. Combining the list of Chandra-detected sources with new optical/IR photometry and optical spectroscopy reveals ~ 165 X-ray bright stars with V < 23. Roughly 142 have optical magnitudes and colors consistent with cluster membership. The observed distribution of Lx peaks at Lx ~ 10^30.3 ergs/s and likely traces the bright edge of a far larger population of ~ 0.4--2 Msun X-ray active stars. From a short list of X-ray active stars with IRAC 8 micron excess from warm, terrestrial-zone dust, we derive a maximum X-ray flux incident on forming terrestrial planets. Although there is no correlation between X-ray activity and IRAC excess, the fractional X-ray luminosity correlates with optical colors and spectral type. By comparing the distribution of Lx/L* vs. spectral type and V-I in h Per with results for other 1--100 Myr-old clusters, we show that stars slightly more massive than the Sun (> 1.5 Msun) fall out of X-ray saturation by ~ 10--15 Myr. Changes in stellar structure for > 1.5 Msun stars likely play an important role in this decline of X-ray emission.
In this paper we present a detailed study of the peculiar early-type galaxy NGC1947. The main goal of this work is to constrain the dynamical status and the formation history of NGC1947 by comparing the observed properties with the predictions derived from different galaxy formation scenarios. To this aim, we derived the photometric and kinematical properties of NGC1947. Due to the presence of an extended dust-lane, which crosses the galaxy center along the photometric minor axis, we used near-infrared images (J and K bands) to derive an accurate analysis of the stellar light distribution. Optical images (in the V and R bands) are used to derive the color profiles and color maps to study the structure of the dust-lane. The observed kinematics confirm the presence of two components with decoupled angular momentum: gas and dust rotate along the minor axis, while the rotation velocities of the stars are observed along the major axis. The complex structure observed in NGC1947 support the hypothesis that some kind of interactions happened in the evolution of this object. We analyzed two alternatives: a merging process and an accretion event. We discussed how the observed properties strongly suggest that the decoupled ring of gas and dust have been accreted from outside.
Observations indicate that mass accretion rates onto low-mass protostars are generally lower than the rates of infall to their disks; this suggests that much of the protostellar mass must be accreted during rare, short outbursts of rapid accretion. We explore when protostellar disk accretion is likely to be highly variable. While constant $\alpha$ disks can in principle adjust their accretion rates to match infall rates, protostellar disks are unlikely to have constant $\alpha$. In particular we show that neither models with angular momentum ransport due solely to the magnetorotational instability (MRI) nor ravitational instability (GI) are likely to transport disk mass at rotostellar infall rates over the large range of radii needed to move infalling envelope material down to the central protostar. We show that the MRI and GI are likely to combine to produce outbursts of rapid accretion starting at a few AU. Our analysis is consistent with the time-dependent models of Armitage, Livio, & Pringle (2001) and agrees with our observational study of the outbursting object FU Ori.
The recent suggestion that late time quantum dynamics may be important for resolving cosmological issues associated with our observed universe requires a consideration of several subtle issues associated with quantum cosmology, as we describe here. The resolution of these issues will be important if we are to be able to properly ascribe probability measures associated with eternal inflation, and a string landscape.
We study the time evolution of the entropy of a collapsing spherical domain wall by investigating the entropy of the entire system (shell-radiation system) and radiation alone during the collapse. By taking the difference, we find the entropy of the collapsing shell, which will collapse and form a black hole. We find that the late time entropy of the collapsing shell is a constant, which is of the same order as the Bekenstein-Hawking entropy.
We present a survey of the theory of the Lyapunov Characteristic Exponents (LCEs) for dynamical systems, as well as of the numerical techniques developed for the computation of the maximal, of few and of all of them. After some historical notes on the first attempts for the numerical evaluation of LCEs, we discuss in detail the multiplicative ergodic theorem of Oseledec \cite{O_68}, which provides the theoretical basis for the computation of the LCEs. Then, we analyze the algorithm for the computation of the maximal LCE, whose value has been extensively used as an indicator of chaos, and the algorithm of the so--called `standard method', developed by Benettin et al. \cite{BGGS_80b}, for the computation of many LCEs. We also consider different discrete and continuous methods for computing the LCEs based on the QR or the singular value decomposition techniques. Although, we are mainly interested in finite--dimensional conservative systems, i. e. autonomous Hamiltonian systems and symplectic maps, we also briefly refer to the evaluation of LCEs of dissipative systems and time series. The relation of two chaos detection techniques, namely the fast Lyapunov indicator (FLI) and the generalized alignment index (GALI), to the computation of the LCEs is also discussed.
We show that a class of bi-gravity theories contain solutions describing dark matter. A particular member of this class is also shown to be equivalent to the Eddington-Born-Infeld gravity, recently proposed as a candidate for dark matter. Bigravity theories also have cosmological de Sitter backgrounds and we find solutions interpolating between matter and acceleration eras.
The spectral index is studied at the point where scalar fields deviate from slow-roll during inflation. Considering the deviation that may cause a significant difference to the time derivative of the Hubble parameter and also to the terms in the evolution equation, we show how the deviation affects the spectral index of the curvature perturbations. Considering conventional inflation, curvatons and other inhomogeneous scenarios as mechanisms for generating the cosmological perturbation, we examine whether the spectral index induced by the deviation from the standard slow-roll can explain the spectral index n-1>0 at k=0.002/Mpc while keeping n-1<0 at a smaller scale.
We investigate the restrictions on the equation-of-state parameter of phantom cosmology, due to the minimum quantum gravitational requirements. We find that for all the examined $w_\Lambda(z)$-parametrizations and for arbitrary phantom potentials and spatial curvature, the phantom equation-of-state parameter is not restricted at all. This is in radical contrast with the quintessence paradigm, and makes phantom cosmology more robust and capable of constituting the underlying mechanism for dark energy.
Observational data from supernovae type Ia, baryon acoustic oscillations, gas mass fraction in galaxy clusters, and the growth factor are used to reconstruct the the interaction rate of the holographic dark energy model recently proposed by Zimdahl and Pav\'{o}n [1] in the redshift interval $0 < z < 1.8$. It shows a reasonable behavior as it increases with expansion from a small or vanishing value in the far past and begins decreasing at recent times. This suggests that the equation of state parameter of dark energy does not cross the phantom divide line.
Following on after two previous papers discussing the formation of primordial black holes in the early universe, we present here results from an in-depth investigation of the extent to which primordial black hole formation in the radiative era can be considered as an example of the critical collapse phenomenon. We focus on initial supra-horizon-scale perturbations of a type which could have come from inflation, with only a growing component and no decaying component. In order to study perturbations with amplitudes extremely close to the supposed critical limit, we have modified our previous computer code with the introduction of an adaptive mesh refinement scheme. This has allowed us to follow black hole formation from perturbations whose amplitudes are up to eight orders of magnitude closer to the threshold than we could do before. We find that scaling-law behaviour continues down to the smallest black hole masses that we are able to follow and we see no evidence of shock production such as has been reported in some previous studies and which led there to a breaking of the scaling-law behaviour at small black-hole masses. We attribute this difference to the different initial conditions used. In addition to the scaling law, we also present other features of the results which are characteristic of critical collapse in this context.
We study the motion of a D3 brane moving within a Type IIB string vacuum compactified to 4D on K3 x T_2/Z_2 in the presence of D7 and O7 planes. We work within the effective 4D supergravity describing how the mobile D3 interacts with the lightest bulk moduli of the compactification, including the effects of modulus-stabilizing fluxes. We seek inflationary solutions to the resulting equations, performing our search numerically in order to avoid resorting to approximate parameterizations of the low-energy potential. We consider uplifting from D-terms and from the supersymmetry-breaking effects of anti-D3 branes. We find examples of slow-roll inflation (with anti-brane uplifting) with the mobile D3 moving along the toroidal directions, falling towards a D7-O7 stack starting from the antipodal point. The inflaton turns out to be a linear combination of the brane position and the axionic partner of the K3 volume modulus, and the similarity of the potential along the inflaton direction with that of racetrack inflation leads to the prediction n_s \le 0.95 for the spectral index. The slow roll is insensitive to most of the features of the effective superpotential, and requires a one-in-10^4 tuning to ensure that the torus is close to square in shape. We also consider D-term inflation with the D3 close to the attractive D7, but find that for a broad (but not exhaustive) class of parameters the conditions for slow roll tend to destabilize the bulk moduli. In contrast to the axionic case, the best inflationary example of this kind requires the delicate adjustment of potential parameters (much more than the part-per-mille level), and gives inflation only at an inflection point of the potential (and so suffers from additional fine-tuning of initial conditions to avoid an overshoot problem).
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Magnetic layers are narrow regions where the field direction changes sharply. They often occur in the association with neutral points of the magnetic field. We show that an organised field can produce these structures near a rotating black hole, and we identify them as potential sites of magnetic reconnection. To that end we study the field lines affected by the frame-dragging effect, twisting the magnetic structure and changing the position of neutral points. We consider oblique fields in vacuum. We also include the possibility of translational motion of the black hole which may be relevant when the black hole is ejected from the system. The model settings apply to the innermost regions around black holes with the ergosphere dominated by a super-equipartition magnetic field and loaded with a negligible gas content.
[Abridged] We present the evolution of the stellar mass function (SMF) of galaxies from z=4.0 to z=1.3 measured from a sample constructed from the deep NIR MUSYC, the FIRES, and the GOODS-CDFS surveys, all having very high-quality optical to mid-infrared data. This sample, unique for its combination of depth and surveyed area, allowed us to 1) minimize the uncertainty due to cosmic variance and empirically quantify its contribution to the total error budget; 2) probe the high-mass end with unprecedented good statistics; 3) empirically derive the redshift-dependent completeness limits in stellar mass; 4) probe the low-mass end of the SMF down to ~0.05 times the characteristic stellar mass. We provide, for the first time, a comprehensive analysis of random and systematic uncertainties affecting the derived SMFs. We find that the mass density evolves by a factor of ~17 since z=4.0, and a factor of ~4 since z=1.3. The evolution appears to be mostly driven by a change in the normalization Phi* but we also find evidence for evolution in the shape of the SMF, with the low-mass end evolving more rapidly than the high-mass end. This result is formally significant, but we show that it is no longer robust when the systematic uncertainties due to different SED-modeling assumptions are taken into account. Taking our results at face value, we find that they are in conflict with semi-analytic models of galaxy formation.
In this paper we present computations of the integrated metal-ion column densities produced in the post-shock cooling layers behind fast, radiative shock-waves. For this purpose, we have constructed a new shock code that calculates the non-equilibrium ionization and cooling; follows the radiative transfer of the shock self-radiation through the post-shock cooling layers; takes into account the resulting photoionization and heating rates; follows the dynamics of the cooling gas; and self-consistently computes the initial photoionization state of the precursor gas. We discuss the shock structure and emitted radiation, and study the dependence on the shock velocity, magnetic field, and gas metallicity. We present a complete set of integrated post-shock and precursor metal-ion column densities of all ionization stages of the elements H, He, C, N, O, Ne, Mg, Si, S, and Fe, for shocks with velocities of 600 and ~2000 km/s, corresponding to initial post-shock temperatures of 5e6 and 5e7 K, cooling down to 1000 K. We consider shocks in which the magnetic field is negligible (B=0) so that the cooling occurs at approximately constant pressure ("isobaric"), and shocks in which the magnetic pressure dominates everywhere such that the cooling occurs at constant density (isochoric). We present results for gas metallicities Z ranging from 1e-3 to twice the solar abundance of heavy elements, and we study how the observational signatures of fast radiative shocks depend on Z. We present our numerical results in convenient online figures and tables, available at this http URL
We announce the discovery of an extended emission line region associated with a high redshift type-2 QSO. The halo, which was discovered in our new wide-field narrow-band survey, resides at z = 2.85 in the Spitzer First Look Survey region and is extended over ~80 kpc. Deep VLBI observations imply that approximately 50 per cent of the radio emission is extended on scales > 200pc. The inferred AGN luminosity is sufficient to ionize the extended halo, and the optical emission is consistent with being triggered coevally with the radio source. The Lyman-alpha halo is as luminous as those found around high redshift radio galaxies, however the active nucleus is several orders of magnitude less luminous at radio wavelengths than those FRIIs more commonly associated with extended emission line regions. AMS05 appears to be a high-redshift analogue to the radio-quiet quasar E1821+643 which is core dominated but which also exhibits extended FRI-like structure and contains an optically powerful AGN. We also find evidence for more quiescent kinematics in the Lyman-alpha emission line in the outer regions of the halo, reminiscent of the haloes around the more powerful FRIIs. The optical to mid-infrared SED is well described by a combination of an obscured QSO (L_bol ~3.4 +/- 0.2 x 10^13 Lsolar) and a 1.4 Gyr old simple stellar population with mass ~3.9 +/- 0.3 x 10^11 Msolar.
The study of the Milky Way stellar discs in the context of galaxy formation is discussed. In particular we explore the properties of the Milky Way disc using a new sample of about 550 dwarf stars for which we have recently obtained elemental abundances and ages based on high resolution spectroscopy. For all the stars we also have full kinematic information as well as information about their stellar orbits. We confirm results from previous studies that the thin and the thick disc have distinct abundance patterns. But we also explore a larger range of orbital parameters than what has been possible in our previous studies. Several new results are presented. We find that stars that reaches high above the galactic plane and have eccentric orbits show remarkably tight abundance trends. This implies that these stars formed out of well mixed gas that had been homogenized over large volumes. We find some evidence that point to that the event that most likely caused the heating of this stellar population happened a few billion years ago. Through a simple, kinematic exploration of stars with super-solar [Fe/H] we show that the solar neighbourhood contains metal-rich, high velocity stars that very likely are associated with the thick disc. Additionally, the HR1614 moving group and the Hercules and Arcturus stellar streams are discussed and it is concluded that, probably, a large fraction of the so far identified groups and streams in the disc are the result of evolution and interactions within the stellar disc rather than being dissolved stellar clusters or engulfed dwarf galaxies.
We report on our observing program to capture simultaneous spectra of Ca II and Balmer lines in a sample of nearby M3 dwarfs. Our goal is to investigate the chromospheric temperature structure required to produce these lines at the observed levels. We find a strong positive correlation between instantaneous measurements of Ca II K and the Balmer lines in active stars, although these lines may not be positively correlated in time-resolved measurements. The relationship between H alpha and Ca II K remains ambiguous for weak and intermediate activity stars, with H alpha absorption corresponding to a range of Ca II K emission. A similar relationship is also observed between Ca II K and the higher order Balmer lines. As our sample consists of a single spectral type, correlations between these important chromospheric tracers cannot be ascribed to continuum effects, as suggested by other authors. These data confirm prior non-simultaneous observations of the H alpha line behavior with increasing activity, showing an initial increase in the H alpha absorption with increasing Ca II K emission, prior to H alpha filling in and eventually becoming a pure emission line in the most active stars. We also compare our optical measurements with archival UV and X-ray measurements, finding a positive correlation between the chromospheric and coronal emission for both high and intermediate activity stars. We compare our results with previous determinations of the active fraction of low mass stars, and discuss them in the context of surface inhomogeneity. Lastly, we discuss the application of these data as empirical constraints on new static models of quiescent M dwarf atmospheres.
This work reports on the development of the first phonon detectors based on CaMoO4 and ZnWO4 scintillating crystals for the CRESST-II experiment. In particular, a novel technique for the production of the ZnWO4 phonon detector with a separate thermometer carrier was investigated. The influence of the thermal and mechanical treatment on the scintillation light output of CaMoO4 and ZnWO4 crystals at room temperature is discussed.
When rotation is not taken into account, the measurement of the Gravitational Redshift can provide unique information about the compactness ($M/R$) of the star. Rotation alters the gravitational redshift rendering thereby a unique determination of the compactness parameter impossible. Nevertheless, it can be shown that by using some theoretical input, useful information on, say, the radii of compact rotating objects can still be extracted. Moreover, by measuring the gravitational redshift one can infer the maximum angular velocity of the object. As it is well known, the minimum observed periods of rotation are found in millisecond pulsars. Here we show that millisecond periods are actually a semi-theoretical limit that can be found by General Relativistic arguments corresponding to the maximum angular velocity. We apply our method to compact objects such as pulsars, white dwarfs and neutron stars.
In our calculation of neutron star crust heating we include several key new model features. In earlier work electron capture (EC) only allowed neutron emission from the daughter ground-state; here we calculate, in a deformed QRPA model, EC decay rates to all states in the daughter that are allowed by Gamow-Teller selection rules and energetics. The subsequent branching ratios between the 1n,...,xn channels and the competing $\gamma$-decay are calculated in a Hauser-Feshbach model. Since EC accesses excited states, many more neutrons are emitted in our calculation than in previous work, leading to accelerated reaction flows. In our multi-component plasma model a single (EC,xn) reaction step can produce several neutron-deficient nuclei, each of which can further decay by (EC,xn). Hence, the neutron emission occurs more continuously with increasing depth as compared to that in a one-component plasma model.
The feasibility and design of an acoustic neutrino detection array in the South Pole ice depend on the acoustic properties of the ice. The South Pole Acoustic Test Setup (SPATS) was built to evaluate the acoustic characteristics of the ice in the 1 to 100kHz frequency range. The vertical sound speed profile relates to the level of refraction of the surface noise and determines the reconstruction precision of the neutrino direction. The SPATS speed of sound analysis for pressure and shear waves is presented.
Recently, Y. Sobouti (2007) has provided a metric theory f(R) that can account for certain dynamical anomalies observed in spiral galaxies. Mendoza & Rosas-Guevara (2007) have shown that in this theory there is an extra-bending as compared to standard general relativity. In the present work we have developed in more specific detail this additional lensing effect and we have made evaluations of the alpha parameter used in the model adjusting the theory to observations in X-rays of 13 clusters of galaxies with gravitational lensing (Hoekstra (2007)).
We have used the Sydney University Stellar Interferometer (SUSI) to measure the angular diameter of the F9 V star beta Virginis. After correcting for limb darkening and combining with the revised Hipparcos parallax, we derive a radius of 1.703 +/- 0.022 R_sun (1.3%). We have also calculated the bolometric flux from published measurements which, combined with the angular diameter, implies an effective temperature of 6059 +/- 49 K (0.8%). We also derived the luminosity of beta Vir to be L = 3.51 +/- 0.08 L_sun (2.1%). Solar-like oscillations were measured in this star by Carrier et al. (2005) and using their value for the large frequency separation yields the mean stellar density with an uncertainty of about 2%. Our constraints on the fundamental parameters of beta Vir will be important to test theoretical models of this star and its oscillations.
Self-Organizing Map (SOM) is a promising tool for exploring large
multi-dimensional data sets. It is quick and convenient to train in an
unsupervised fashion and, as an outcome, it produces natural clusters of data
patterns. An example of application of SOM to the new OGLE-III data set is
presented along with some preliminary results.
Once tested on OGLE data, the SOM technique will also be implemented within
the Gaia mission's photometry and spectrometry analysis, in particular, in
so-called classification-based Science Alerts. SOM will be used as a basis of
this system as the changes in brightness and spectral behaviour of a star can
be easily and quickly traced on a map trained in advance with simulated and/or
real data from other surveys.
We clarify the response of extrasolar planetary systems in a 2:1 mean motion commensurability, with masses ranging from the super Jovian range to the terrestrial range, to stochastic forcing that could result from protoplanetary disk turbulence. The behaviour of the different libration modes for a wide range of system parameters and stochastic forcing magnitudes is investigated. The growth of libration amplitudes is parameterized as a function of the relevant parameters. The results are applied to provide an explanation of the configuration of the HD128311 system. We first develop an analytic model without making the assumption that the eccentricities are small. We also perform numerical N-body simulations with additional stochastic forcing terms to represent the effects of putative disk turbulence. We isolate two distinct libration modes for the resonant angles. These react to stochastic forcing in a different way and become coupled when the libration amplitudes are large. Systems are quickly destabilized by large magnitudes of stochastic forcing but some stability is imparted should systems undergo a net orbital migration. The slow mode, which mostly corresponds to motion of the angle between the apsidal lines of the two planets, is converted to circulation more readily than the fast mode which is associated with oscillations of the semi-major axes. This mode is also vulnerable to the attainment of small eccentricities which causes oscillations between periods of libration and circulation. Stochastic forcing due to disk turbulence may have played a role in shaping the configurations of observed systems in mean motion resonance. It naturally provides a mechanism for accounting for the HD128311 system for which the fast mode librates and the slow mode is apparently near the borderline between libration and circulation.
This paper reports on the first results of the Suzaku observation in the Sgr C region. We detected four diffuse clumps with strong line emission at 6.4keV, Ka from neutral or low-ionized Fe. One of them, M359.38-0.00, is newly discovered with Suzaku. The X-ray spectra of the two bright clumps, M359.43-0.07 and M359.47-0.15, after subtracting the Galactic center diffuse X-ray emission (GCDX), exhibit strong Ka line from FeI with large equivalent widths (EWs) of 2.0-2.2keV and clear Kb of FeI. The GCDX in the Sgr C region is composed of the 6.4keV- and 6.7keV-associated components. These are phenomenologically decomposed by taking relations between EWs of the 6.4keV and 6.7keV lines. Then the former EWs against the associated continuum in the bright clump regions are estimated to be 2.4(+2.3_-0.7)keV. Since the two different approaches give similar large EWs of 2keV, we strongly suggest that the 6.4keV clumps in the Sgr C region are due to X-ray reflection/fluorescence (the X-ray reflection nebulae).
Modeling the structure formation in the universe, we extend the spherical collapse model in the context of MOND starting with the linear Newtonian structure formation followed by the MONDian evolution. In MOND the formation of structures speed up without a need for dark matter. Starting with the top-hat over-dense distribution of the matter, the structures virialize with a power--law profile of the distribution of matter. We show that the virialization process takes place gradually from the center of the structure to the outer layers. In this scenario the smaller structures enter to the MONDian regime earlier and evolve faster, hence they are older than larger structures. We also show that the virialization of the structures occur in the MONDian regime, in which the smaller structures have stronger gravitational acceleration than the larger ones. This feature of the dynamical behavior of the structures is in agreement with this fact that the smaller structures as the globular clusters or galactic bulges have been formed earlier and need less dark matter in CDM scenario.
We present the results of deep and high-resolution (FWHM ~ 0".35) JHK NIR observations with the Subaru telescope, to search for very low mass young stellar objects (YSOs) in the W3 Main star-forming region. The NIR survey covers an area of ~ 2.6 arcmin^2 with 10-sigma limiting magnitude exceeding 20 mag in the JHK bands. The survey is sensitive enough to provide unprecedented details in W3 IRS 5 region and reveals a census of the stellar population down to objects below the hydrogen-burning limit. We construct JHK color-color (CC) and J-H/J and H-K/K color-magnitude (CM) diagrams to identify very low luminosity YSOs and to estimate their masses. Based on these CC and CM diagrams, we identified a rich population of embedded YSO candidates with infrared excesses (Class I and Class II), associated with the W3 Main region. A large number of red sources (H-K > 2) have also been detected around W3 Main. We argue that these red stars are most probably pre-main-sequence (PMS) stars with intrinsic color excesses. Based on the comparison between theoretical evolutionary models of very low-mass PMS objects with the observed CM diagram, we find there exists a substantial substellar population in the observed region. The mass function (MF) does not show the presence of cutoff and sharp turnover around the substellar limit, at least at the hydrogen-burning limit. Furthermore, the MF slope indicates that the number ratio of young brown dwarfs and hydrogen-burning stars in the W3 Main is probably higher than those in Trapezium and IC 348. The presence of mass segregation, in the sense that relatively massive YSOs lie near the cluster center, is seen. The estimated dynamical evolution time indicates that the observed mass segregation in the W3 Main may be the imprint of the star formation process.
We investigate the constraints that can be set from big-bang nucleosynthesis on two classes of models: extended quintessence and scalar-tensor theories of gravity in which the equivalence principle between standard matter and dark matter is violated. In the latter case, and for a massless dilaton with quadratic couplings, the phase space of theories is investigated. We delineate those theories where attraction toward general relativity occurs. It is shown that big-bang nucleosynthesis sets more stringent constraints than those obtained from Solar system tests.
The origin of ultra high energy cosmic rays promises to lead us to a deeper understanding of the structure of matter, through the study of particle collisions at center-of-mass energies in interactions far larger than anything possible with the Large Hadron Collider, albeit at the substantial cost of no control over the sources and interaction sites. For the extreme energies we have to identify and understand the sources first, before trying to use them as physics laboratories. Here we describe the current stage of this exploration. The most promising contenders as sources are radio galaxies and gamma ray bursts. The sky distribution of observed events yields a hint favoring radio galaxies. Key in this quest are the intergalactic and galactic magnetic fields, whose strength and structure are not yet fully understood. Current data and statistics do not yet allow a final judgment. We outline how we may progress in the near future.
We performed cosmological simulations based upon both a cold dark matter (CDM) and a warm dark matter (WDM) model. The focus of our investigations lies with selected spatial and kinematic properties of substructure halos (subhalos) orbiting within host halos, that form in both dark-matter cosmologies. We aim at using the dynamics of the subhalos as a probe of the respective cosmology.
We have analyzed a sample of LBGs from z =3.5 to z=6 selected from the GOODS-S field as B,V and i-dropouts, and with spectroscopic observations showing that they have the Lyalpha line in emission. Our main aim is to investigate their physical properties and their dependence on the emission line characteristics, to shed light on the relation between galaxies with Lyalpha emission and the general LBG population.The objects were selected from their continuum colors and then spectroscopically confirmed by the GOODS collaboration and other campaigns. From the spectra we derived the line flux and EW. We then used U-band to mid-IR photometry from GOODS-MUSIC to derive the physical properties of the galaxies, such as total stellar mass, age and so on, through standard SED fitting techniques.Although most galaxies are fit by young stellar populations, a small but non negligible fraction has SEDs that require considerably older stellar component, up to 1 Gyr. There is no apparent relation between age and EW: some of the oldest galaxies have large EW, and should be also selected in narrow band surveys. Therefore not all Lyalpha emitters are primeval galaxies in the very early stages of formation,as is commonly assumed. We also find a large range of stellar populations, with masses from 5x10^8 Msol to 5x10^10 Msol and SFR from few to 60 Msol/yr. Although there is no correlation between mass and EW, we find a significant lack of massive galaxies with high EW, which could be explained if the most massive galaxies were more dusty and/or contained more neutral gas than less massive objects. Finally we find that more than half of the galaxies contain small but non negligible amounts of dust: the mean E(B-V) and the EW are well correlated, although with a large scatter, as already found at lower redshift
We explore the extinction properties of the dust in the distant universe through the afterglows of high-redshifted GRBs based on the "Drude" model which, unlike previous studies, does not require a prior assumption of template extinction laws. We select GRB070802 at z~2.45 (which shows clear evidence for the 2175\AA extinction bump) and GRB050904 at z~6.29, the 2nd most distant GRB observed to date. We fit their afterglow spectra to determine the extinction of their host galaxies. We find that (1) their extinction curves differ substantially from that of the Milky Way, the Small and Large Magellanic Clouds (which were widely adopted as template extinction laws in literature); (2) the 2175\AA extinction feature appears to be also present in GRB050904 at z~6.29; and (3) there does not appear to show strong evidence for a dependence of dust extinction on redshifts. The inferred extinction curves are closely reproduced in terms of a mixture of amorphous silicate and graphite, both of which are expected supernova condensates and have been identified in primitive meteorites as presolar grains originating from supernovae (which are considered as the main source of dust at high-z).
The MAGIC collaboration reported the detection of a new VHE source, MAGIC J0223+430, located close to the position of the blazar 3C66A, considered a candidate TeV blazar since a long time. A careful analysis showed that the events with energies above 150 GeV are centered on the position of the FRI radiogalaxy 3C66B (at 6 arcmin from 3C66A), with a probability of 95.4% (85.4% including systematic uncertainties) that the source is not related to 3C66A. We present a model for the possible emission of 3C66B based on the structured jet model already used to interpret the TeV emission of the radiogalaxy M87. The model requires parameters similar to those used for M87 but a larger luminosity for the layer, to account for the more luminous TeV emission. We also show that the spectrum obtained by MAGIC can be interpreted as the combined emission of 3C66B, dominating above ~200 GeV, and of 3C66A. The high-energy emission from the latter source, being strongly attenuated by the interaction with the extragalactic background light, can only contribute at low energies. If we were to see the jet emission of 3C 66B at small viewing angles we would see a spectral energy distribution closely resembling the one of S5 0716+714, a typical blazar.
Recently radio signals originating from extensive air showers have been observed at the Pierre Auger Observatory. In this note we present software to simulate the response of an array of antenna detectors and to reconstruct the radio signals. With this software it is possible to investigate design parameters of an antenna array and to visualize the radio data. We show comparisons between measurements of radio signals from air showers and simulated data which were generated with the REAS2 generator and then processed with the detector simulation and reconstruction software.
Two key parameters that describe a massive black hole are the spin and mass of the hole. Substantial progress has been made toward determining the masses of black holes. Here, a new approach to constraining or determining the spin of a massive black hole, obtained by combining the outflow energy and mass of the hole, is proposed and applied to test the magnetically switched, rotating black hole model of Meier (1999). A sample of 19 powerful classical double radio galaxies is studied. It is found that the minimum spin value of each of the black holes is greater than 0.1, in agreement with the predictions of the magnetically switched model. A sample of 29 central dominant galaxies is also studied. It is found that almost all of the sources with clear FRI structure have minimum spin values less than 0.1, again in agreement with predictions. In addition, the spin values of the FRI sources range from about 0.001 to 0.1, in agreement with the range predicted by the magnetically switched model.
The coronal structure of main sequence stars continues to puzzle us. While the solar corona is relatively well understood, it has become clear that even stars of the same mass as the Sun can display very non-solar coronal behaviour, particularly if they are rapid rotators or in a binary system. At masses greater than and also less than that of the Sun, the non-solar internal structure appears to affect both the geometry and dynamics of the stellar corona and the nature of the X-ray and radio emission. In this talk I will describe some recent advances in our understanding of the structure of the coronae of some of the most active (and interesting) main sequence stars.
It has been known for some time now that rapidly-rotating solar-like stars
possess the stellar equivalent of solar prominences. These may be three orders
of magnitude more massive than their solar counterparts, and their ejection
from the star may form a significant contribution to the loss of angular
momentum and mass in the stellar wind. In addition, their number and
distribution provide valuable clues as to the structure of the stellar corona
and hence to the nature of magnetic activity in other stars.
Until recently, these "slingshot prominences" had only been observed in
mature stars, but their recent detection in an extremely young star suggests
that they may be more widespread than previously thought. In this review I will
summarise our current understanding of these stellar prominences, their
ejection from their stars and their role in elucidating the (sometimes very
non-solar) behaviour of stellar magnetic fields.
We examine relationships between the morphology in double radio sources and the radio-optical position angle offset--the relative orientation of the radio axis with respect to the major axis of the host galaxy. The study was done for a representative sample of radio sources: the nearby (redshift z < 0.5) 3CRR sources, and separately for samples of giant radio sources and X-shaped radio sources. We find that radio morphological features have a dependence on the radio-optical position angle offset and on whether the source is a major- or minor-axis source. The evidence indicates an anisotropic galaxy environment, related to the ellipticity of the host galaxy, that causes the source linear size evolution, strength of backflow in the radio lobes, off-axis lobe distortions and the formation of wings and X-shaped radio sources to depend on the radio-optical position angle offset. We identify a class of X-shaped radio sources, which are either edge-darkened or lacking hotspots, and appear to have inner doubles suggesting a restarting of activity. We suggest a common formation mechanism, requiring backflows, for these apparently FR-I X-shaped radio sources as well as the edge-brightened X-shaped sources.
LOPES is set up at the location of the KASCADE-Grande extensive air shower experiment in Karlsruhe, Germany and aims to measure and investigate radio pulses from Extensive Air Showers. Since radio waves suffer very little attenuation, radio measurements allow the detection of very distant or highly inclined showers. These waves can be recorded day and night, and provide a bolometric measure of the leptonic shower component. LOPES is designed as a digital radio interferometer using high bandwidths and fast data processing and profits from the reconstructed air shower observables of KASCADE-Grande. The LOPES antennas are absolutely amplitude calibrated allowing to reconstruct the electric field strength which can be compared with predictions from detailed Monte Carlo simulations. We report about the analysis of correlations present in the radio signals measured by the LOPES 30 antenna array. Additionally, LOPES operates antennas of a different type (LOPES-STAR) which are optimized for an application at the Pierre Auger Observatory. Status, recent results of the data analysis and further perspectives of LOPES and the possible large scale application of this new detection technique are discussed.
Supermassive black hole binaries (SMBHBs) with masses in the range 10^4-10^7 M_sun/(1+z), produced in galaxy mergers, are thought to complete their coalescence due to the emission of gravitational waves (GWs). The anticipated detection of the GWs by the LISA will constitute a milestone for fundamental physics and astrophysics. While the GW signatures themselves will provide a treasure trove of information, if the source can be securely identified in electromagnetic (EM) bands, this would open up entirely new scientific opportunities, to probe fundamental physics, astrophysics, and cosmology. We discuss several ideas, involving wide-field telescopes, that may be useful in locating electromagnetic counterparts to SMBHBs detected by LISA. In particular, the binary may produce a variable electromagnetic flux, such as a roughly periodic signal due to the orbital motion prior to coalescence, or a prompt transient signal caused by shocks in the circumbinary disk when the SMBHB recoils and "shakes" the disk. We discuss whether these time-variable EM signatures may be detectable, and how they can help in identifying a unique counterpart within the localization errors provided by LISA. We also discuss a possibility of identifying a population of coalescing SMBHBs statistically, in a deep optical survey for periodically variable sources, before LISA detects the GWs directly. The discovery of such sources would confirm that gas is present in the vicinity and is being perturbed by the SMBHB - serving as a proof of concept for eventually finding actual LISA counterparts.
A step feature in the inflaton potential can model a transient breakdown of slow-roll inflation. Here we generalize the step feature to include space-dependence, allowing it also to model a breakdown of homogeneity and isotropy. The space-dependent inflaton potential generates a classical curvature perturbation mode characterized by the wavenumber of the step inhomogeneity. For inhomogeneities small compared with the horizon at the step, space-dependence has a small effect on the curvature perturbation. Therefore the smoothly oscillating quantum power spectrum predicted by the homogeneous step is robust with respect to sub-horizon space-dependence. For inhomogeneities equal to or greater than the horizon at the step, the space-dependent classical mode can dominate, producing a curvature perturbation in which modes of wavenumber determined by the step inhomogeneity are superimposed on the oscillating power spectrum. Generation of a space-dependent step feature may therefore provide a mechanism to introduce primordial anisotropy into the curvature perturbation. Space-dependence also modifies the quantum fluctuations, in particular via resonance-like features coming from mode coupling to amplified superhorizon modes. However these effects are small relative to the classical modes.
The extended nebulae formed as pulsar winds expand into their surroundings provide information about the composition of the winds, the injection history from the host pulsar, and the material into which the nebulae are expanding. Observations from across the electromagnetic spectrum provide constraints on the evolution of the nebulae, the density and composition of the surrounding ejecta, the geometry of the systems, the formation of jets, and the maximum energy of the particles in the nebulae. Here I provide a broad overview of the structure of pulsar wind nebulae, with specific examples that demonstrate our ability to constrain the above parameters. The association of pulsar wind nebulae with extended sources of very high energy gamma-ray emission are investigated, along with constraints on the nature of such high energy emission.
A canonic scalar field minimally coupled to a disformal metric generated by the field itself is considered. Causality and stability conditions are derived for such a field. Cosmological effects are studied and it is shown that the disformal modification could viably trigger an acceleration after a scaling matter era, thus possibly alleviating the coincidence problem.
LS 5039 is a TeV gamma-ray binary with extended radio emission. It consists of a compact object in the mildly eccentric (e=0.35), 3.9-day orbit around a massive O star. The nature of the compact object is not yet established. In this paper, assuming that the compact object is a black hole, we study the accretion of O-star wind by the black hole, by performing three-dimensional Smoothed Particle Hydrodynamics (SPH) simulations. In order to roughly emulate the effect of the stellar radiation effectively canceling the stellar gravity, we assume that the O star's gravity does not exert on the wind. The wind particles are ejected with half the observed terminal velocity in a narrow range of azimuthal and vertical angles toward the black hole, in order to emulate the wind significantly slower than the terminal speed, and optimize the resolution and computational efficiency of simulations. We find that the mass-accretion rate closely follows the classical Bondi-Hoyle-Littleton accretion rate, which is of the order of 10^{16}g/s around periastron. The accretion rate at this level would provide jets enough power to produce the gamma-rays detected by HESS. Since the accretion peak occurs near the periastron passage, we need a strong gamma-ray absorption around periastron in order for the microquasar scenario to be consistent with the observed orbital modulation of the TeV gamma-ray flux.
We present a review on bar pattern speeds from preliminary results in the context of the Nuclei of Galaxies (NUGA) project. The large variety of molecular circumnuclear morphologies found in NUGA is a challenging result that implies the refinement of current dynamical models of galaxies.
We report the detection of a new transient radio source, GCRT J1742-3001, located ~1 degree from the Galactic center. The source was detected ten times from late 2006 to 2007 May in our 235 MHz transient monitoring program with the Giant Metrewave Radio Telescope (GMRT). The radio emission brightened in about one month, reaching a peak observed flux density of ~100 mJy on 2007 January 28, and decaying to ~50 mJy by 2007 May when our last monitoring observation was made. Two additional faint, isolated 235 MHz detections were made in mid-2006, also with the GMRT. GCRT J1742-3001 is unresolved at each epoch, with typical resolutions of ~20 arcsec x 10 arcsec. No polarization information is available from the observations. Based on nondetections in observations obtained simultaneously at 610 MHz, we deduce that the spectrum of GCRT J1742-3001 is very steep, with a spectral index less than about -2. Follow-up radio observations in 2007 September at 330 MHz and 1.4 GHz, and in 2008 February at 235 MHz yielded no detections. No X-ray counterpart is detected in a serendipitous observation obtained with the X-ray telescope aboard the Swift satellite during the peak of the radio emission in early 2007. We consider the possibilities that GCRT J1742-3001 is either a new member of an existing class of radio transients, or is representative of a new class having no associated X-ray emission.
We have obtained radial velocity measurements for stars in two, widely-separated fields in the Anticenter Stream. Combined with SDSS/USNO-B proper motions, the new measurements allow us to establish that the stream is on a nearly circular, somewhat inclined, prograde orbit around the Galaxy. While the orbital eccentricity is similar to that previously determined for the Monoceros stream, the sizes, inclinations, and positions of the orbits for the two systems differ significantly. Integrating our best fitting Anticenter Stream orbit forward, we find that it is closely aligned along and lies almost on top of a stream-like feature previously designated the "Eastern Banded Structure". The position of this feature coincides with the apogalacticon of the orbit. We tentatively conclude that this feature is the next wrap of the Anticenter Stream.
Recent imaging campaigns indicate the possible existence of massive planets on longer than 1000 year orbits about a few percent of normal stars. Such objects are not easily explained in most current planet formation models. In this Letter we use a large ensemble of N-body simulations to evaluate the potential for planet scattering during relaxation of dynamically active systems to explain very long period, massive planets. We find that such a mechanism could indeed be at play, and that statistical samples of long period planets could place interesting constraints on early stage planet formation scenarios. Results from direct imaging and microlensing surveys are complementary probes of this dynamical relaxation process.
We present two models for the cosmological UV background light, and calculate the opacity of GeV gamma--rays out to redshift 9. The contributors to the background include 2 possible quasar emissivities, and output from star--forming galaxies as determined by recent a semi--analytic model (SAM) of structure formation. The SAM used in this work is based upon a hierarchical build-up of structure in a $\Lambda$CDM universe and is highly successful in reproducing a variety of observational parameters. Above 1 Rydberg energy, ionizing radiation is subject to reprocessing by the IGM, which we treat using our radiative transfer code, CUBA. The two models for quasar emissivity differing above z = 2.3 are chosen to match the ionization rates observed using flux decrement analysis and the higher values of the line-of-sight proximity effect. We also investigate the possibility of a flat star formation rate density at z $>5$. We conclude that observations of gamma--rays from 10 to 100 GeV by Fermi (GLAST) and the next generation of ground based experiments should confirm a strongly evolving opacity from $1<$ z $<4$. Observation of attenuation in the spectra of gamma--ray bursts at higher redshift could constrain emission of UV radiation at these early times, either from a flat or increasing star-formation density or an unobserved population of sources.
The next-to-leading order (NLO) QCD corrections are calculated to pair-annihilation of spin-1 bosonic dark matter (DM) by dimensionally regularizing both ultraviolet and infrared singularities in non-relativistic limit. The complete O(alpha_s) correction is about 8% in the case considered only massless gluon and about 13%, when included the massive gluon at 1TeV. The NLO QCD correction could shift the DM mass window constrained by WMAP and improve the observability in the projected direct detector, GENIUS.
We study the possibility that a keV-MeV mass hidden photon (HP), i.e. a hidden sector U(1) gauge boson, accounts for the observed amount of dark matter. We focus on the case where the HP interacts with the standard model sector only through kinetic mixing with the photon. The relic abundance is computed including all relevant plasma effects into the photon's self-energy, which leads to a resonant yield almost independent of the HP mass. The HP can decay into three photons. Moreover, if light enough it can be copiously produced in stars. Including bounds from cosmic photon backgrounds and stellar evolution, we find that the hidden photon can only give a subdominant contribution to the dark matter. This negative conclusion may be avoided if another production mechanism besides kinetic mixing is operative.
The missing of a Keplerian fall-off in the observed galaxy rotation curves represents classical evidence for the existence of dark matter on galactic scales. There has been some recent activity concerning the potential of modelling galactic systems with the help of general relativity. This was motivated by claims that by the use of full general relativity dark matter could be made superfluous. Here we focus on possible axisymmetric and stationary solutions of Einstein's equations with rotating dust. After a short review of the current debate we pursue the idea of approaching such relativistic models in a Newtonian language. We analyse rigidly as well as differentially rotating Newtonian and Post-Newtonian spacetimes and find that it is necessary to incorporate a Post-Newtonian term in order to make physical sense.
Astrophysical and cosmological observations do not require the dark matter particles to be absolutely stable. If they are indeed unstable, their decay into positrons might occur at a sufficiently large rate to allow the indirect detection of dark matter through an anomalous contribution to the cosmic positron flux. In this paper we discuss the implications of the excess in the positron fraction recently reported by the PAMELA collaboration for the scenario of decaying dark matter. To this end, we have performed a model-independent analysis of possible signatures by studying various decay channels in the case of both a fermionic and a scalar dark matter particle. We find that the steep rise in the positron fraction measured by PAMELA at energies larger than 10 GeV can naturally be accommodated in several realizations of the decaying dark matter scenario.
We study the evolution of maximally symmetric $p$-branes with a $S_{p-i}\otimes \mathbbm{R}^i$ topology in flat expanding or collapsing homogeneous and isotropic universes with $N+1$ dimensions (with $N \ge 3$, $p < N$, $0 \le i < p$). We find the corresponding equations of motion and compute new analytical solutions for the trajectories in phase space. For a constant Hubble parameter, $H$, and $i=0$ we show that all initially static solutions with a physical radius below a certain critical value, $r_c^0$, are periodic while those with a larger initial radius become frozen in comoving coordinates at late times. We find a stationary solution with constant velocity and physical radius, $r_c$, and compute the root mean square velocity of the periodic $p$-brane solutions and the corresponding (average) equation of state of the $p$-brane gas. We also investigate the $p$-brane dynamics for $H \neq {\rm constant}$ in models where the evolution of the universe is driven by a perfect fluid with constant equation of state parameter, $w={\cal P}_p/\rho_p$, and show that a critical radius, $r_c$, can still be defined for $ -1 \le w < w_c$ with $w_c=(2-N)/N$. We further show that for $w \sim w_c$ the critical radius is given approximately by $r_c H \propto (w_c-w)^{\gamma_c}$ with $\gamma_c=-1/2$ ($r_c H \to \infty$ when $w \to w_c$). Finally, we discuss the impact that the large scale dynamics of the universe can have on the macroscopic evolution of very small loops.
It is well known that the viscous Bianchi type-I metric of the Kasner form is not able to describe an anisotropic universe, which satisfies the second law of thermodynamics and the dominant energy condition in Einstein's theory of gravity. We investigate this problem in Brans-Dicke theory of gravity using the Bianchi type-I metric with the perfect fluid. We show that it is possible to have the dominant energy condition and the growth of entropy in this model. Also we apply this model to explain the anomaly concerning the low quadrupole amplitude of the angular power spectrum of the temperature anisotropy observed in WMAP data.
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Following the optical imaging of the exoplanet candidate Fomalhaut b (Fom b), we present a numerical model of how Fomalhaut's debris disk is gravitationally shaped by a single interior planet. The model is simple, adaptable to other debris disks, and can be extended to accommodate multiple planets. We find that to not disrupt the belt, Fom b must have a mass < 3 Jupiter masses. Previous mass constraints based on disk morphology rely on several oversimplifications. We explain why our constraint is more reliable. It is based on a global model of the disk that is not restricted to the planet's chaotic zone boundary. Moreover, we screen disk parent bodies for dynamical stability over the system age of 100 Myr, and model them separately from their dust grain progeny; the latter's orbits are strongly affected by radiation pressure and their lifetimes are limited to 0.1 Myr by destructive grain-grain collisions. The single planet model predicts that planet and disk orbits be apsidally aligned. Preliminary analysis of Fom b's space velocity does not bear this out. The disagreement might be resolved by having additional perturbers in the Fomalhaut system, for which there is independent evidence from the star's anomalous Hipparcos acceleration. Our upper mass limit of 3 Jupiter masses for Fom b is not affected by these considerations. The belt contains at least 3 Earth masses of solids that are grinding down to dust. Such a large mass in solids is consistent with Fom b having formed in situ.
We have compiled a sample of early-type cluster galaxies from 0 < z < 1.3 and measured the evolution of their ellipticity distributions. Our sample contains 487 galaxies in 17 z>0.3 clusters with high quality space-based imaging and a comparable sample of 210 galaxies in 10 clusters at z<0.05. We select early-type galaxies (elliptical and S0 galaxies) that fall within the cluster R_{200}, and which lie on the red-sequence in the magnitude range -19.3 > M_B > -21, after correcting for luminosity evolution. Our ellipticity measurements are made in a consistent manner over our whole sample. We perform extensive simulations to quantify the systematic and statistical errors, and find that it is crucial to use PSF-corrected model fits. We find that neither the median ellipticity, nor the shape of the ellipticity distribution of cluster early-type galaxies evolves with redshift from z ~ 0 to z > 1. These results are strongly suggestive of an unchanging overall bulge-to-disk ratio distribution for cluster early-type galaxies over the last ~8Gyr. This result contrasts with that from visual classifications which show that the fraction of morphologically-selected disk-dominated early-type galaxies, or S0s, is significantly lower at z>0.4 than at z~0. Taking the ellipticity measurements and assuming, as in all previous studies, that the intrinsic ellipticity distribution of both elliptical and S0 galaxies remains constant, then we conclude from the lack of evolution in the observed early-type ellipticity distribution that the relative fractions of ellipticals and S0s do not evolve from z~1 to z=0 for a red-sequence selected samples of galaxies in the cores of clusters of galaxies.
To examine the role of the host galaxy structure in fueling nuclear activity, we estimated gas flow rates from several kpc down to the inner few 10 pc for seven nearby spiral galaxies, selected from the NUGA sample (NUclei of GAlaxies). We calculated gravitational torques from near-IR images and determined gas in/out-flow rates as a function of radius and location within the galactic disks, based on high angular resolution interferometric observations of molecular (CO using PdBI) and atomic (HI using the VLA) gas. The results are compared with kinematic evidence for radial gas flows and the dynamical state of the galaxies (via resonances) derived from several different methods. We show that gravitational torques are very efficient at transporting gas from the outer disk all the way into the galaxies centers at ~100 pc; previously assumed dynamical barriers to gas transport, such as the Corotation Resonance of stellar bars, seem to be overcome by gravitational torque induced gas flows from other non-axisymmmetric structures. The resulting rates of gas mass inflow range from 0.01 to 50 solar masses per year and are larger for the galaxy center than for the outer disk. Our gas flow maps show the action of nested bars within larger bars for 3 galaxies. Non-circular streaming motions found in the kinematic maps are larger in the center than in the outer disk and appear to correlate only loosely with the in/out-flow rates as a function of radius. We demonstrate that spiral gas disks are very dynamic systems that undergo strong radial evolution on timescales of a few rotation periods (e.g. 5 times 10^8 yrs at a radius of 5 kpc), due to the effectiveness of gravitational torques in redistributing the cold galactic gas.
(abridged) We develop an algorithm for estimating parameters of a distribution sampled with contamination, employing a statistical technique known as ``expectation maximization'' (EM). Given models for both member and contaminant populations, the EM algorithm iteratively evaluates the membership probability of each discrete data point, then uses those probabilities to update parameter estimates for member and contaminant distributions. The EM approach has wide applicability to the analysis of astronomical data. Here we tailor an EM algorithm to operate on spectroscopic samples obtained with the Michigan-MIKE Fiber System (MMFS) as part of our Magellan survey of stellar radial velocities in nearby dwarf spheroidal (dSph) galaxies. These samples are presented in a companion paper and contain discrete measurements of line-of-sight velocity, projected position, and Mg index for ~1000 - 2500 stars per dSph, including some fraction of contamination by foreground Milky Way stars. The EM algorithm quantifies both dSph and contaminant distributions, returning maximum-likelihood estimates of the means and variances, as well as the probability that each star is a dSph member. Applied to our MMFS data, the EM algorithm identifies more than 5000 probable dSph members. We test the performance of the EM algorithm on simulated data sets that represent a range of sample size, level of contamination, and amount of overlap between dSph and contaminant velocity distributions. The simulations establish that for samples ranging from large (N ~3000) to small (N~30), the EM algorithm distinguishes members from contaminants and returns accurate parameter estimates much more reliably than conventional methods of contaminant removal (e.g., sigma clipping).
We present the main results of a numerical study of weak lensing cluster counting. We examine the scaling with cosmology of the projected-density-peak mass function. Our main conclusion is that the projected-peak and the 3-D mass functions scale with cosmology in an astonishingly close way. This means that, despite being derived from a 2-D field, the weak lensing cluster abundance can be used to constrain cosmology in the same way as the 3-D mass function probed by other types of surveys.
Fomalhaut is a bright star 7.7 parsecs (25 light years) from Earth that harbors a belt of cold dust with a structure consistent with gravitational sculpting by an orbiting planet. Here, we present optical observations of an exoplanet candidate, Fomalhaut b. In the plane of the belt, Fomalhaut b lies approximately 119 astronomical units (AU) from the star, and within 18 AU of the dust belt. We detect counterclockwise orbital motion using Hubble Space Telescope observations separated by 1.73 years. Dynamical models of the interaction between the planet and the belt indicate that the planet's mass is at most three times that of Jupiter for the belt to avoid gravitational disruption. The flux detected at 800 nm is also consistent with that of a planet with mass no greater than a few times that of Jupiter. The brightness at 600 nm and the lack of detection at longer wavelengths suggest that the detected flux may include starlight reflected off a circumplanetary disk, with dimension comparable to the orbits of the Galilean satellites. We also observed variability of unknown origin at 600 nm.
Based on the Sloan Digital Sky Survey DR6 (SDSS) and Millennium Simulation (MS) we investigate the alignment between galaxies and large-scale structure. For this purpose we develop two new statistical tools, namely the alignment correlation function and the cos(2theta)-statistic. The former is a two-dimensional extension of the traditional two-point correlation function and the latter is related to the ellipticity correlation function used for cosmic shear measurements. Both are based on the cross correlation between a sample of galaxies with orientations and a reference sample which represents the large-scale structure. Applied to the SDSS galaxy catalog the alignment correlation function reveals an overabundance of reference galaxies along the major axes of red, luminous (L > L*) galaxies out to projected separations of 60 Mpc/h. No alignment signal is detected for blue galaxies. The cos(2\theta)-statistic yields very similar results. Starting from a MS semi-analytic galaxy catalog we assign an orientation to each red, luminous and central galaxy, based on the central region of the host halo. Alternatively, we use the orientation of the host halo itself. We find a mean projected misalignment between a halo and its central region of ~25 deg. Agreement with the SDSS results is good if the central orientations are used. Using the halo orientations overestimates the observed alignment by more than a factor of 2. The large volume of the MS allows to generate two-dimensional maps of the alignment correlation function which show the reference galaxy distribution to be flattened parallel to the orientations of red luminous galaxies with axis ratios of ~0.5 and ~0.75 for halo and central orientations,respectively. These ratios are almost independent of scale out to 60 Mpc/h.
We present a search for Trojan companions to 25 transiting exoplanets. We use the technique of Ford & Gaudi, in which a difference is sought between the observed transit time and the transit time that is calculated by fitting a two-body Keplerian orbit to the radial-velocity data. This technique is sensitive to the imbalance of mass at the L4/L5 points of the planet-star orbit. No companions were detected above 2\sigma confidence. The median 2\sigma upper limit is 56 M_\earth, and the most constraining limit is 2.8 M_\earth for the case of GJ 436. A similar survey using forthcoming data from the Kepler satellite mission, along with the radial-velocity data that will be needed to confirm transit candidates, will be sensitive to 10-50 M_\earth Trojan companions in the habitable zones of their parent stars. As a by-product of this study, we present empirical constraints on the eccentricities of the planetary orbits, including those which have previously been assumed to be circular. The limits on eccentricity are of interest for investigations of tidal circularization and for bounding possible systematic errors in the measured planetary radii and the predicted times of secondary eclipses.
We present high spatial resolution optical and near-infrared imaging obtained using the ACS, WFPC2 and NICMOS cameras aboard the Hubble Space Telescope of 31 24um--bright z~2 Dust Obscured Galaxies (DOGs) identified in the Bootes Field of the NOAO Deep Wide-Field Survey. Although this subset of DOGs have mid-IR spectral energy distributions dominated by a power-law component suggestive of an AGN, all but one of the galaxies are spatially extended and not dominated by an unresolved component at rest-frame UV or optical wavelengths. The observed V-H and I-H colors of the extended components are 0.2-3 magnitudes redder than normal star-forming galaxies. All but 1 have axial ratios >0.3, making it unlikely that DOGs are composed of an edge-on star-forming disk. We model the spatially extended component of the surface brightness distributions of the DOGs with a Sersic profile and find effective radii of 1-6 kpc. This sample of DOGs is smaller than most sub-millimeter galaxies (SMGs), but larger than quiescent high-redshift galaxies. Non-parametric measures (Gini and M20) of DOG morphologies suggest that these galaxies are more dynamically relaxed than local ULIRGs. We estimate lower limits to the stellar masses of DOGs based on the rest-frame optical photometry and find that these range from ~10^(9-11) M_sun. If major mergers are the progenitors of DOGs, then these observations suggest that DOGs may represent a post-merger evolutionary stage.
High-energy cosmic rays, with energies of 10^12 eV or more, have often been considered a powerful way to constrain Planck-scale physics that generates energy-dependent speeds of light. While it is simple to think of these signals as arising from preferred-frame effects, many quantum gravity theories require the first postulate of Special Relativity hold at all energies. Here we examine how a consistent phenomenology for cosmic-ray observers can be constructed, and we present the relationship between observables such as photon time delays and the underlying theory. We find the usual assumptions about Planck scale phenomenology have in some cases only limited domains of applicability for astrophysical systems, but demonstrate how they may be modified to cure these problems.
In this Paper, we have derived Cepheid period-luminosity (P-L) relations for the Large Magellanic Cloud (LMC) fundamental mode Cepheids, based on the data released from OGLE-III. We have applied an extinction map to correct for the extinction of these Cepheids. In addition to the VIW band P-L relations, we also include JHK and four Spitzer IRAC band P-L relations, derived by matching the OGLE-III Cepheids to the 2MASS and SAGE datasets, respectively. We also test the non-linearity of the Cepheid P-L relations based on extinction-corrected data. Our results (again) show that the LMC P-L relations are non-linear in VIJH bands and linear in KW and the four IRAC bands, respectively.
We describe a Bayesian approach to estimating quasar black hole mass functions (BHMF) when using the broad emission lines to estimate black hole mass. We show how using the broad line mass estimates in combination with statistical techniques developed for luminosity function estimation leads to statistically biased results. We derive the likelihood function for the BHMF based on the broad line mass estimates, and derive the posterior distribution for the BHMF, given the observed data. We develop our statistical approach for a flexible model where the BHMF is modelled as a mixture of Gaussian functions. Statistical inference is performed using markov chain monte carlo (MCMC) methods. Our method has the advantage that it is able to constrain the BHMF even beyond the survey detection limits at the adopted confidence level, accounts for measurement errors and the intrinsic uncertainty in broad line mass estimates, and provides a natural way of estimating the probability distribution of any quantities derived from the BHMF. We conclude by using our method to estimate the local active BHMF using the z < 0.5 Bright Quasar Survey sources. At z = 0.2, the quasar BHMF falls off approximately as a power law with slope ~ 2 for M_{BH} > 10^8. Our analysis implies that z < 0.5 broad line quasars have a typical Eddington ratio of ~ 0.4 and a dispersion in Eddington ratio of < 0.5 dex (abridged).
We present new results on the frequency distribution of projected HI column densities f(N,X), total comoving covering fraction, and integrated mass densities rho_HI of high redshift, HI `disks' from a survey of damped Lya systems (DLAs) in the Sloan Digital Sky Survey, Data Release 5. For the full sample spanning z=2.2 to 5 [738 DLAs], f(N,X) is well fitted by a double power-law with a break column density N_d = 10^(21.55 +/- 0.04) and low/high-end exponents alpha = -2.00 +/- 0.05, -6.4^{+1.1}_{-1.6}. The shape of f(N,X) is invariant during this redshift interval and also follows the projected surface density distribution of present-day HI disks as inferred from 21cm observations. We conclude that HI gas has been distributed in a self-similar fashion for the past 12Gyr. The normalization of f(N,X), in contrast, decreases by a factor of two during the ~2Gyr interval from z=4 to 2.2 giving corresponding decreases in both the total covering fraction and rho_HI. At z~2, these quantities match the present-day values suggesting no evolution during the past ~10Gyr. We argue that the evolution at early times is driven by `violent' processes that removes gas from nearly half the galaxies at z~3 establishing the antecedants of current early-type galaxies. The perceived constancy of rho_HI, meanwhile, implies that HI gas is a necessary but insufficient pre-condition for star formation and that the global star-formation rate is driven by the accretion and condensation of fresh gas from the intergalactic medium.
We describe a new code to search for signatures of cosmic strings in cosmic microwave anisotropy maps. The code implements the Canny Algorithm, an edge detection algorithm designed to search for the lines of large gradients in maps. Such a gradient signature which is coherent in position space is produced by cosmic strings via the Kaiser-Stebbins effect. We test the power of our new code to set limits on the tension of the cosmic strings by analyzing simulated data with and without cosmic strings. We compare maps with a pure Gaussian scale-invariant power spectrum with maps which have a contribution of a distribution of cosmic strings obeying a scaling solution. The maps have angular scale and angular resolution comparable to what current and future ground-based small-scale cosmic microwave anisotropy experiments will achieve. We present tests of the codes, indicate the limits on the string tension which could be set with the current code, and describe various ways to refine the analysis. Our results indicate that when applied to the data of ongoing cosmic microwave experiments such as the South Pole Telescope project, the sensitivity of our method to the presence of cosmic strings will be more than an order of magnitude better than the limits from existing analyses.
Digital Access to a Sky Century @ Harvard (DASCH) is a project to digitize
the collection of ~500,000 glass photographic plates held at Harvard College
Observatory. The collection spans the time period from 1880 to 1985, during
which time every point on the sky has been observed approximately 500 to 1000
times.
In this paper we describe the results of the DASCH commissioning run, during
which we developed the data-reduction pipeline and fine-tuned the digitzer's
performance and operation. This initial run consisted of 500 plates taken from
a variety of different plate-series, all containing the open cluster Praeseppe
(M44). We report that accurate photometry at the 0.1mag level is possible on
the majority of plates, and demonstrate century-long light-curves of various
types of variable stars in and around M44.
Bekenstein's Tensor-Vector-Scalar (TeVeS) theory has had considerable success in explaining various phenomena without the need for dark matter. However, it is difficult to observationally discern the differences between TeVeS and predictions made within the Lambda-cold dark matter concordance model. This implies that alternative tests are required that independently verify which theory is correct. For this we turn to the strong-field regime of TeVeS. In particular, we solve the spherically symmetric equations of hydrostatic equilibrium for a perfect fluid with a realistic equation of state to build models of neutron stars in TeVeS. We show that causality within the neutron star is only maintained for certain cosmological values of the scalar field, which allows us to put constraints on this value independently of cosmological observations. We also discuss in detail the internal structure of neutron stars and how each of the free parameters in the theory effects the overall size and mass of the neutron stars. In particular, the radii of neutron stars in TeVeS can significantly differ from those in General Relativity for certain values of the vector field coupling, which allows us to also place extra constraints on this parameter. Finally, we discuss future observations of neutron stars using both the electromagnetic and gravitational wave spectrums that will allow for tests of the appropriate theory of gravity.
I review recent studies of the emission-line regions in Orion and M17. Both have similar geometries, a bubble of hot shocked gas surrounding the central star cluster, with H^+, H^0, and H_2 regions, often referred to as H II regions, PDRs, and molecular clouds, forming successive shells on the surface of a molecular cloud. The magnetic fields in the H^0 regions have been measured with 21 cm Zeeman polarization and are found to be 1 -- 2 dex stronger than the field in the diffuse ISM. The regions appear to be in rough hydrostatic equilibrium. The H^+ region is pushed away from the star cluster by starlight radiation pressure. Since most starlight is in ionizing radiation, most of its outward push will act on the H^+ region and then on to the H^0 region. The magnetic pressure in the H^0 region balances the momentum in starlight and together they set the location of the H^0 region. The picture is that, when the star cluster formed, it created a bubble of ionized gas which expanded and compressing surrounding H^0 and H_2 regions. The magnetic field was amplified until its pressure was able to support the momentum in starlight. This offers a great simplification in understanding the underlying physics that establishes parameters for PDR models.
We study the Milky Way region Z<3.0 kpc, where the thick disk and inner halo overlap, by using the kinematics of local blue horizontal branch (BHB) stars (within 1 kpc) and new samples of BHB stars and A-type stars from the Century Survey. We derive Galactic U,V,W velocities for these BHB and A-type star samples using proper motions from the NOMAD catalog. The mean velocities and the velocity dispersions of the BHB samples (Z<3 kpc) are characteristic of the halo, while those of the Century Survey A-type stars are characteristic of the thick disk. There is no evidence from our samples that the BHB stars rotate with the thick disk in the region Z<3 kpc. Nearly a third of the nearby local RR Lyrae stars have disk kinematics and are more metal-rich than [Fe/H]~-1. Only a few percent of the Century Survey BHB stars have these properties. Only one nearby BHB star (HD 130201) is likely to be such a disk star but selection based on high proper motions will have tended to exclude such stars from the local sample. The scale height derived from a sample of local RR Lyrae stars agrees with that of the Century Survey BHB stars. The local samples of BHB stars and metal-weak red giants are too incomplete for a similar comparison.
We show that current clustering observations of quasars and luminous AGN can be explained by a merger model augmented by feedback from outflows. Using numerical simulations large enough to study clustering out to 25 comoving h^{-1} Mpc, we calculate correlation functions, biases, and correlation lengths as a function of AGN redshift and optical and X-ray luminosity. At optical wavelengths, our results match a wide range of current observations and generate predictions for future data sets. We reproduce the weak luminosity dependence of clustering over the currently well-measured range, and predict a much stronger dependence at higher luminosities. The increase in the amplitude of binary quasar clustering observed in the Sloan Digital Sky Survey (SDSS) is also reproduced and is predicted to occur at higher redshift, an effect that is due to the one halo term in the correlation function. On the other hand, our results do not match the rapid evolution of the correlation length observed in the SDSS at z\simeq 3, a discrepancy that is at least partially due to differences in the scales probed by our simulation versus this survey. In fact, we show that changing the distances sampled from our simulations can produce changes as large as 40% in the fitted correlation lengths. Finally, in the X-ray, our simulations produce correlation lengths similar to that observed in the Chandra Deep Field (CDF) North, but not the significantly larger correlation length observed in the CDF South.
We report the discovery of PSR J1753-2240 in the Parkes Multibeam Pulsar Survey database. This 95-ms pulsar is in an eccentric binary system with a 13.6-day orbital period. Period derivative measurements imply a characteristic age in excess of 1 Gyr, suggesting that the pulsar has undergone an episode of accretion-induced spin-up. The eccentricity and spin period are indicative of the companion being a second neutron star, so that the system is similar to that of PSR J1811-1736, although other companion types cannot be ruled out at this time. The companion mass is constrained by geometry to lie above 0.48 solar masses, although long-term timing observations will give additional constraints. If the companion is a white dwarf or main sequence star, optical observations may yield a direct detection of the companion. If the system is indeed one of the few known double neutron star systems, it would lie significantly far from the recently proposed spin-period/eccentricity relationship.
It is widely assumed that the observed reduction of the magnetic field of millisecond pulsars can be connected to the accretion phase during which the pulsar is spun up by mass accretion from a companion. A wide variety of reduction mechanisms have been proposed, including the burial of the field by a magnetic mountain, formed when the accreted matter is confined to the poles by the tension of the stellar magnetic field. A magnetic mountain effectively screens the magnetic dipole moment. On the other hand, observational data suggests that accreting neutron stars are sources of gravitational waves, and magnetic mountains are a natural source of a time-dependent quadrupole moment. We show that the emission is sufficiently strong to be detectable by current and next generation long-baseline interferometers. Preliminary results from fully three-dimensional magnetohydrodynamic (MHD) simulations are presented. We find that the initial axisymmetric state relaxes into a nearly axisymmetric configuration via toroidal magnetic modes. A substantial quadrupole moment is still present in the final state, which is stable (in ideal MHD) yet highly distorted.
We propose a unified model to explain Quasi-Periodic-Oscillation (QPO), particularly of high frequency, observed from black hole and neutron star systems globally. We consider accreting systems to be damped harmonic oscillators exhibiting epicyclic oscillations with higher order nonlinear resonance to explain QPO. The resonance is expected to be driven by the disturbance from the compact object at its spin frequency. The model explains various properties parallelly for both types of the compact object. It describes QPOs successfully for ten different compact sources. Based on it, we predict the spin frequency of the neutron star Sco X-1 and specific angular momentum of black holes GRO J1655-40, XTE J1550-564, H1743-322, GRS 1915+105.
An accretion flow is necessarily transonic around a black hole. However, around a neutron star it may or may not be transonic, depending on the inner disk boundary conditions influenced by the neutron star. I will discuss various transonic behavior of the disk fluid in general relativistic (or pseudo general relativistic) framework. I will address that there are four types of sonic/critical point possible to form in an accretion disk. It will be shown that how the fluid properties including location of sonic points vary with angular momentum of the compact object which controls the overall disk dynamics and outflows.
We present the results of Spectral Energy Distribution(SED) fitting analysis for Lyman Break Galaxies(LBGs) at z~5 in the GOODS-N and its flanking fields (the GOODS-FF). With the publicly available IRAC images in the GOODS-N and IRAC data in the GOODS-FF, we constructed the rest-frame UV to optical SEDs for a large sample (~100) of UV-selected galaxies at z~5. Comparing the observed SEDs with model SEDs generated with a population synthesis code, we derived a best-fit set of parameters (stellar mass, age, color excess, and star formation rate) for each of sample LBGs. The derived stellar masses range from 10^8 to 10^11M_sun with a median value of 4.1x10^9M_sun. The comparison with z=2-3 LBGs shows that the stellar masses of z~5 LBGs are systematically smaller by a factor of 3-4 than those of z=2-3 LBGs in a similar rest-frame UV luminosity range. The star formation ages are relatively younger than those of the z=2-3 LBGs. We also compared the results for our sample with other studies for the z=5-6 galaxies. Although there seem to be similarities and differences in the properties, we could not conclude its significance. We also derived a stellar mass function of our sample by correcting for incompletenesses. Although the number densities in the massive end are comparable to the theoretical predictions from semi-analytic models, the number densities in the low-mass part are smaller than the model predictions. By integrating the stellar mass function down to 10^8 M_sun, the stellar mass density at z~5 is calculated to be (0.7-2.4)x10^7M_sun Mpc^-3. The stellar mass density at z~5 is dominated by massive part of the stellar mass function. Compared with other observational studies and the model predictions, the mass density of our sample is consistent with general trend of the increase of the stellar mass density with time.
We derive the mass-metallicity relation of star-forming galaxies up to $z\sim0.9$, using data from the VIMOS VLT Deep Survey. Automatic measurement of emission-line fluxes and equivalent widths have been performed on the full spectroscopic sample. This sample is divided into two sub-samples depending on the apparent magnitude selection: wide ($I_{\mathrm{AB}}<22.5$) and deep $I_{\mathrm{AB}}<24$). These two samples span two different ranges of stellar masses. Emission-line galaxies have been separated into star-forming galaxies and active galactic nuclei using emission line ratios. For the star-forming galaxies the emission line ratios have also been used to estimate gas-phase oxygen abundance, using empirical calibrations renormalized in order to give consistent results at low and high redshifts. The stellar masses have been estimated by fitting the whole spectral energy distributions with a set of stellar population synthesis models. We assume at first order that the shape of the mass-metallicity relation remains constant with redshift. Then we find a stronger metallicity evolution in the wide sample as compared to the deep sample. We thus conclude that the mass-metallicity relation is flatter at higher redshift. The observed flattening of the mass-metallicity relation at high redshift is analyzed as an evidence in favor of the open-closed model.
We investigate the structure of dynamics of large self-gravitating astrophysical systems using a self-interacting two-component model. We consider two cases, galaxy clusters and cosmic walls, for illustrations. In both cases stability analyses are conducted using perturbative expansion. We have found that waves and solitons are easily generated in these systems. Our analysis shows that dark matter can be Jeans unstable in the very inner regions of galaxy clusters if it has a large internal degree of freedom. The dark matter core may collapse under external perturbations. We also discuss dark-matter oscillations in galaxy clusters and how mode growth and decay lead to heating of intracluster medium. Our analysis shows that dark-matter solitons with both positive and negative amplitudes can be excited in cosmic walls. Resonances in soliton interaction could enhance gas condensation. The co-existence of the two types of dark-matter solitons implies that bright filaments can arise in dark voids.
We present a convariant formulation for radiative transfer in curved space time and demonstrate some applications in the black-hole systems. We calculate the emission from semi-transparent accretion tori around black holes, for opacity provided by the Fe K lines and for opacity dominated by electron scattering. We also calculate the emission from radiative inefficient accretion flow in black holes with opacity provided by electron-positron annihilation lines. Finally we show shadows cast by accreting black holes with different spins and with different distribution of warm material around them.
We obtain the chemical abundances of six barium stars and two CH subgiant stars based on the high signal-to-noise ratio and high resolution Echelle spectra. The neutron capture process elements Y, Zr, Ba, La, Eu show obvious overabundance relative to the Sun, for example, their [Ba/Fe] values are from 0.45 to 1.27. Other elements, including Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Ni, show comparable abundances to the Solar ones, and their [Fe/H] cover a range from $-$0.40 to 0.21, which means they belong to Galactic disk. The predicts of the theoretical model of wind accretion for binary systems can explain the observed abundance patterns of the neutron capture process elements in these stars, which means that their overabundant heavy-elements could be caused by accreting the ejecta of AGB stars, the progenitors of the present white dwarf companions in the binary systems.
Aims. We present a continuation of our study about the relation between stellar mass and gas-phase metallicity in the VIMOS VLT Deep Survey (VVDS). In this work we extend the determination of metallicities up to redshift = 1.24 for a sample of 42 star-forming galaxies with a mean redshift value of 0.99. Methods. For a selected sample of emission-line galaxies, we use both diagnostic diagrams and empirical calibrations based on [OII] emission lines along with the empirical relation between the intensities of the [OIII] and [NeIII] emission lines and the theoretical ratios between Balmer recombination emission lines to identify star-forming galaxies and to derive their metallicities. We derive stellar masses by fitting the whole spectral energy distribution with a set of stellar population synthesis models. Results. These new methods allow us to extend the mass-metallicity relation to higher redshift. We show that the metallicity determinations are consistent with more established strong-line methods. Taken together this allows us to study the evolution of the mass-metallicity relation up to z = 1.24 with good control of systematic uncertainties. We find an evolution with redshift of the average metallicity of galaxies very similar to those reported in the literature: for a given stellar mass, galaxies at z = 1 have, on average, a metallicity = 0.3 dex lower than galaxies in the local universe. However we do not see any significant metallicity evolution between redshifts z = 0.7 (Paper I) and z = 1.0 (this paper). We find also the same flattening of the mass-metallicity relation for the most massive galaxies as reported in Paper I at lower redshifts, but again no apparent evolution of the slope is seen between z = 0.7 and z = 1.0.
A few Type Ia supernovae (SNe Ia) have been suggested to be an explosion of a super-Chandrasekhar-mass white dwarf (WD) to account for their large luminosities, requiring a large amount of 56Ni. However, the candidate over-luminous SNe Ia 2003fg, 2006gz, and (moderately over-luminous) SN 1991T, have very different observational features: the characteristic time-scale and velocity are very different. We examine if and how the diversity can be explained, by 1D spherical radiation transport calculations covering a wide range of model parameters (e.g., WD mass). The observations of SN 2006gz are naturally explained by the super-Chandrasekhar-mass model. SN 1991T represents a marginal case, which may either be a Chandrasekhar or a super-Chandrasekhar-mass WD explosion. On the other hand, the low velocity and short time-scale seen in SN 2003fg indicate that the ejecta mass is smaller than the Chandrasekhar-mass, which is an apparent contradiction to the large luminosity. We suggest that the problem is solved if the progenitor WD, and thus the SN explosion, is aspherical. This may reflect a rapid rotation of the progenitor star, likely a consequence of the super-Chandrasekhar-mass WD progenitor. The observed differences between SNe 2003fg and 2006gz may be attributed to different viewing orientations.
With construction halfway complete, IceCube is already the most sensitive neutrino telescope ever built. A rearrangement of the final holes of IceCube with increased spacing has been discussed recently to optimize the high energy sensitivity of the detector. Extending this baseline with radio and acoustic instrumentation in the same holes could further improve the high energy response. The goal would be both to detect events and to act as a pathfinder for hybrid detection, towards a possible larger hybrid array. Simulation results for such an array are presented here.
We report resolved photometry of the primary and secondary components of 23 transneptunian binaries obtained with the Hubble Space Telescope. V-I colors of the components range from 0.7 to 1.5 with a median uncertainty of 0.06 magnitudes. The colors of the primaries and secondaries are correlated with a Spearman rank correlation probability of 99.99991%, 5 sigma for a normal distribution. Fits to the primary vs. secondary colors are identical to within measurement uncertainties. The color range of binaries as a group is indistinguishable from that of the larger population of apparently single transneptunian objects. Whatever mechanism produced the colors of apparently single TNOs acted equally on binary systems. The most likely explanation is that the colors of transneptunian objects and binaries alike are primordial and indicative of their origin in a locally homogeneous, globally heterogeneous protoplanetary disk.
Large amount of observational spectroscopic data are recently available from different observational projects, like Sloan Digital Sky Survey. It's become more urgent to identify white dwarfs stars based on data itself i.e. without modelling white dwarf atmospheres. In particular, existing methods of white dwarfs identification presented in Kleinman et al. (2004) and in Eisenstein et al. (2006) did not allow to find all the white dwarfs in examined data. We intend to test various criteria of searching for white dwarf candidates, based on photometric and spectral features.
We discuss the results of 3D simulations of tidal disruptions of white dwarfs by moderate-mass black holes as they may exist in the cores of globular clusters or dwarf galaxies. Our simulations follow self-consistently the hydrodynamic and nuclear evolution from the initial parabolic orbit over the disruption to the build-up of an accretion disk around the black hole. For strong enough encounters (pericentre distances smaller than about 1/3 of the tidal radius) the tidal compression is reversed by a shock and finally results in a thermonuclear explosion. These explosions are not restricted to progenitor masses close to the Chandrasekhar limit, we find exploding examples throughout the whole white dwarf mass range. There is, however, a restriction on the masses of the involved black holes: black holes more massive than $2\times 10^5$ M$_\odot$ swallow a typical 0.6 M$_\odot$ dwarf before their tidal forces can overwhelm the star's self-gravity. Therefore, this mechanism is characteristic for black holes of moderate masses. The material that remains bound to the black hole settles into an accretion disk and produces an X-ray flare close to the Eddington limit of $L_{\rm Edd} \simeq 10^{41} {\rm erg/s} M_{\rm bh}/1000 M$_\odot$), typically lasting for a few months. The combination of a peculiar thermonuclear supernova together with an X-ray flare thus whistle-blows the existence of such moderate-mass black holes. The next generation of wide field space-based instruments should be able to detect such events.
We use oblate axisymmetric dynamical models including dark halos to determine the orbital structure of intermediate mass to massive Coma early-type galaxies. We find a large variety of orbital compositions. Averaged over all sample galaxies the unordered stellar kinetic energy in the azimuthal and the radial direction are of the same order, but they can differ by up to 40 percent in individual systems. In contrast, both for rotating and non-rotating galaxies the vertical kinetic energy is on average smaller than in the other two directions. This implies that even most of the rotating ellipticals are flattened by an anisotropy in the stellar velocity dispersions. Using three-integral axisymmetric toy models we show that flattening by stellar anisotropy maximises the entropy for a given density distribution. Collisionless disk merger remnants are radially anisotropic. The apparent lack of strong radial anisotropy in observed early-type galaxies implies that they may not have formed from mergers of disks unless the influence of dissipational processes was significant.
We present predictions for the abundance and nature of Extremely Red Objects (EROs) in the Lambda cold dark matter model. EROs are red, massive galaxies observed at z>= 1 and their numbers and properties pose a challenge to hierarchical galaxy formation models. We compare the predictions from two published models, one of which invokes a ``superwind'' to regulate star formation in massive haloes and the other which suppresses gas cooling in haloes through ``radio-mode'' AGN feedback. The superwind model underestimates the number counts of EROs by an order of magnitude, whereas the radio-mode AGN feedback model gives excellent agreement with the number counts and redshift distribution of EROs. In the AGN feedback model the ERO population is dominated by old, passively evolving galaxies, whereas observations favour an equal split between old galaxies and dusty starbursts. Also, the model predicts a more extended redshift distribution of passive galaxies than is observed. These comparisons suggest that star formation may be quenched too efficiently in this model.
A spectral-line survey of IRC+10216 in the 345 GHz band has been undertaken with the Submillimeter Array. Although not yet completed, it has already yielded a fairly large sample of narrow molecular emission lines with line-widths indicating expansion velocities of ~4 km/s, less than 3 times the well-known value of the terminal expansion velocity (14.5 km/s) of the outer envelope. Five of these narrow lines have now been identified as rotational transitions in vibrationally excited states of previously detected molecules: the v=1, J=17--16 and J=19--18 lines of Si34S and 29SiS and the v=2, J=7--6 line of CS. Maps of these lines show that the emission is confined to a region within ~60 AU of the star, indicating that the narrow-line emission is probing the region of dust-formation where the stellar wind is still being accelerated.
Motivated by the closest major merger, the Antennae Galaxies (NGC4038/4039), we want to improve our genetic algorithm based modeling code Minga (Theis 1999). The aim is to reveal the major interaction and galaxy parameters, e.g. orbital information and halo properties of such an equal mass merger system. Together with the sophisticated search strategy of Minga, one needs fast and reliable models in order to investigate the high dimensional parameter space of this problem. Therefore we use a restricted N-body code which is based on the approach by Toomre & Toomre (1972), however with some refinements like consistent orbits of extended dark matter halos. Recently also dynamical friction was included to this code (Petsch 2007). While a good description for dynamical friction was found for mass ratios up to q = 1/3 (Petsch & Theis 2008), major merger systems were only imperfectly remodeled. Here we show recent improvements for a major merger system by including mass-loss and using NFW halos.
We analyse whether hierarchical formation models based on Lambda cold dark matter cosmology can produce enough massive red galaxies to match observations. For this purpose, we compare with observations the predictions from two published models for the abundance and redshift distribution of Extremely Red Objects (EROs), which are red, massive galaxies observed at z >= 1. One of the models invokes a ``superwind'' to regulate star formation in massive haloes and the other suppresses cooling through ``radio-mode'' AGN feedback. The first one underestimates the number counts of EROs by an order of magnitude, whereas the radio-mode AGN feedback model gives excellent agreement with the number counts of EROs and redshift distribution of K-selected galaxies. This study highlights the need to consider AGN feedback in order to understand the formation and evolution of massive galaxies at z >= 1.
The Standard Model of cosmology states a surprising composition of the Universe, in which ordinary matter accounts for less than 5%. The remaining 95% are composed of ~70% Dark Energy and ~25% Dark Matter. However, those two components have never been identified and remain a challenging problem to modern cosmology. One alternative to the concordance model could be the symmetric Milne universe, composed of matter and antimatter (supposed to have negative mass) in equal quantities. We will present the effects of these hypothesis on classical cosmological tests such as primordial nucleosynthesis, CMB, or Type Ia supernovae and show that this model is in remarkably good agreement with observations.
We investigate the possibility that the E_p propto E_gamma^{1/2} relation between the peak energy E_p of the nuF_nu spectrum and energy output E_gamma for long-duration GRBs arises from the external shock produced by the interaction of a relativistic outflow with the ambient medium. To that aim, we take into account the dependence of all parameters which determine E_p and E_gamma on the radial distribution of the ambient medium density and find that the E_p-E_gamma relation can be explained if the medium around GRBs has a universal radial stratification. For various combinations of GRB radiative process (synchrotron or inverse-Compton) and dissipation mechanism (reverse or forward shock), we find that the circumburst medium must have a particle density with a radial distribution different than the R^{-2} expected for constant mass-loss rate and terminal speed.
We consider contributions to non-Gaussianity of the Cosmic Microwave Background (CMB) from remnants of post-inflationary phase transitions in the very early universe. Such signatures can optimistically be used to discover evidence of new particle physics through cosmological observations. More conservatively they provide a potential obstacle to extracting information about the non-Gaussian nature of primordial density fluctuations from any detection in the CMB. We demonstrate this explicitly by computing the bispectrum from global textures, which may be generated from a wide class of particle physics models.
We present a method to recover mass profiles of galaxy clusters by combining data on thermal Sunyaev-Zeldovich (tSZ) and X-ray imaging, thereby avoiding to use any information on X-ray spectroscopy. This method, which represents a development of the geometrical deprojection technique presented in Ameglio et al. (2007), implements the solution of the hydrostatic equilibrium equation. In order to quantify the efficiency of our mass reconstructions, we apply our technique to a set of hydrodynamical simulations of galaxy clusters. We propose two versions of our method of mass reconstruction. Method 1 is completely model-independent, while Method 2 assumes instead the analytic mass profile proposed by Navarro et al. (1997) (NFW). We find that the main source of bias in recovering the mass profiles is due to deviations from hydrostatic equilibrium, which cause an underestimate of the mass of about 10 per cent at r_500 and up to 20 per cent at the virial radius. Method 1 provides a reconstructed mass which is biased low by about 10 per cent, with a 20 per cent scatter, with respect to the true mass profiles. Method 2 proves to be more stable, reducing the scatter to 10 per cent, but with a larger bias of 20 per cent, mainly induced by the deviations from equilibrium in the outskirts. To better understand the results of Method 2, we check how well it allows to recover the relation between mass and concentration parameter. When analyzing the 3D mass profiles we find that including in the fit the inner 5 per cent of the virial radius biases high the halo concentration. Also, at a fixed mass, hotter clusters tend to have larger concentration. Our procedure recovers the concentration parameter essentially unbiased but with a scatter of about 50 per cent.
We measure the local galaxy far-infrared (FIR) 60-to-100 um colour-luminosity distribution using an all-sky IRAS survey. This distribution is an important reference for the next generation of FIR--submillimetre surveys that have and will conduct deep extra-galactic surveys at 250--500 um. With the peak in dust-obscured star-forming activity leading to present-day giant ellipticals now believed to occur in sub-mm galaxies near z~2.5, these new FIR--submillimetre surveys will directly sample the SEDs of these distant objects at rest-frame FIR wavelengths similar to those at which local galaxies were observed by IRAS. We have taken care to correct for temperature bias and evolution effects in our IRAS 60 um-selected sample. We verify that our colour-luminosity distribution is consistent with measurements of the local FIR luminosity function, before applying it to the higher-redshift Universe. We compare our colour-luminosity correlation with recent dust-temperature measurements of sub-mm galaxies and find evidence for pure luminosity evolution of the form (1+z)^3. This distribution will be useful for the development of evolutionary models for BLAST and SPIRE surveys as it provides a statistical distribution of rest-frame dust temperatures for galaxies as a function of luminosity.
We study the thermodynamics of tidal charged black holes in four dimensions. Such black holes are spherically symmetric vacuum solutions of the effective Einstein equations on the brane and are characterized by the mass m and (generalizing their general relativistic counterparts) by a second parameter, the tidal charge q. The latter is an imprint of the Weyl curvature of the 5-dimensional space-time, in which the brane is embedded. The heat capacity of the tidal charged black hole diverges on a set of measure zero of the parameter space. However, there is no phase transition at those points, similarly to the Reissner-Nordstr\"om black hole. We investigate the thermodynamic geometry of such black holes by deriving the Weinhold and the Ruppeiner metrics. Whereas the Weinhold metric is flat, the Ruppeiner metric has a positive Ricci curvature, which is in sharp contrast with the Reissner-Nordstr\"om black hole, the general relativistic analogue of the tidal charged metric. The state space is conformal to the right half of the interior of the future light cone in a Minkowski plane. We find two constraints on the possible 5-dimensional extensions of the tidal-charged black hole: First, we conjecture that the 5-dimensional black object should have the same entropy as its 4-dimensional section studied here, modulo corrections which are small for large black holes. Second, for constant m any quasi-stationary evolution of the tidal charged black hole leads to a decrease of q, contributing towards the localization of gravity on the brane. This represents an important constraint on the evolution of the 5-dimensional space-time.
We study a possible dark matter candidate in the framework of a minimal anomalous U(1)' extension of the MSSM. It turns out that in a suitable decoupling limit the axino, which is present in the Stuckelberg multiplet, is the lightest supersymmetric particle (LSP). We compute the relic density of this particle including coannihilations with the next to lightest supersymmetric particle (NLSP) which is assumed almost degenerate in mass with the LSP. This assumption is needed in order to satisfy the stringent limits that the Wilkinson Microwave Anisotropy Probe (WMAP) put on the relic density. We find that in the parameter space region where the model remains perturbative the axino fulfills the WMAP constraints.
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