Astrophysics
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New submissions for Fri, 14 Nov 08
- [1] arXiv:0811.1985 [ps, pdf, other]
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Title: Fomalhaut's Debris Disk and Planet: Constraining the Mass of Fomalhaut b From Disk MorphologyAuthors: E. Chiang (UCB), E. Kite (UCB), P. Kalas (UCB), J. R. Graham (UCB), M. Clampin (NASA Goddard Space Flight Center)Comments: Accepted to the Astrophysical Journal, 17 pages, 11 figures. Companion theory paper to Science discovery paper. See the movie at this http URLSubjects: Astrophysics (astro-ph)
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.
- [2] arXiv:0811.1986 [ps, pdf, other]
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Title: The Ellipticities of Cluster Early-type Galaxies from z~1 to z~0: No Evolution in the Overall Distribution of Bulge-to-Disk RatiosAuthors: B. P. Holden, M. Franx, G. D. Illingworth, M. Postman, A. van der Wel, D. D. Kelson, J. P. Blakeslee, H. Ford, R. Demarco, S. MeiComments: 21 pages, 15 color figures, accepted in ApJSubjects: Astrophysics (astro-ph)
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.
- [3] arXiv:0811.1988 [pdf, other]
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Title: Dynamical Evolution of AGN Host Galaxies - Gas In/Out-Flow Rates in 7 NUGA GalaxiesAuthors: Sebastian Haan (1), Eva Schinnerer (1), Eric Emsellem (2), Santiago Garcia-Burillo (3), Francoise Combes (4), Carole G. Mundell (5), Hans-Walter Rix (1) ((1)MPIA-Heidelberg-Germany, (2)CRAL-Observatoire de Lyon-France, (3)OAN-Madrid-Spain, (4)LERMA-Paris-France, (5)LJMU-Liverpool-UK)Comments: 83 pages, 13 figures, accepted for publication in ApJ. The full-resolution version is available at this http URLSubjects: Astrophysics (astro-ph)
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.
- [4] arXiv:0811.1990 [ps, pdf, other]
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Title: Clean Kinematic Samples in Dwarf Spheroidals: An Algorithm for Evaluating Membership and Estimating Distribution Parameters When Contamination is PresentComments: Accepted for publication in The Astronomical Journal. Download pdf with full-resolution figures from this http URLSubjects: Astrophysics (astro-ph)
(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).
- [5] arXiv:0811.1991 [ps, pdf, other]
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Title: The cosmology dependence of weak lensing cluster countsComments: 4 pages, 2 figures. Submitted to PRLSubjects: Astrophysics (astro-ph)
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.
- [6] arXiv:0811.1994 [ps, pdf, other]
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Title: Optical Images of an Exosolar Planet 25 Light Years from EarthAuthors: Paul Kalas (1), James R. Graham (1), Eugene Chiang (1,2), Michael P. Fitzgerald (3), Mark Clampin (4), Edwin S. Kite (2), Karl Stapelfeldt (5), Christian Marois (6), John Krist (5) ((1) Astronomy Department, University of California, Berkeley, CA, USA (2) Department of Earth & Planetary Science, University of California, Berkeley, CA, USA (3) Lawrence Livermore National Laboratory, Livermore, CA, USA (4) Goddard Space Flight Center, Greenbelt, MD, USA (5) Jet Propulsion Laboratory, Pasadena, CA, USA (6) Herzberg Institute for Astrophysics, Victoria, BC, Canada)Comments: 25 pages; 4 tables; 4 figures. To appear in Science November 13, 2008Subjects: Astrophysics (astro-ph)
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.
- [7] arXiv:0811.1995 [ps, pdf, other]
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Title: Alignment between galaxies and large-scale structureComments: submitted to RAASubjects: Astrophysics (astro-ph)
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.
- [8] arXiv:0811.1996 [ps, pdf, other]
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Title: Empirical Constraints on Trojan Companions and Orbital Eccentricities in 25 Transiting Exoplanetary SystemsComments: Accepted for publication in The Astrophysical Journal (11 pages, in emulateapj format)Subjects: Astrophysics (astro-ph)
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.
- [9] arXiv:0811.1997 [ps, pdf, other]
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Title: HST Morphologies of z~2 Dust Obscured Galaxies I: Power-law SourcesAuthors: R. S. Bussmann, Arjun Dey, J. Lotz, L. Armus, K. Brand, M. J. I. Brown, V. Desai, P. Eisenhardt, J. Higdon, S. Higdon, B. T. Jannuzi, E. Le Floc'h, J. Melbourne, B. T. Soifer, D. WeedmanComments: 23 pages, 9 figures, 6 tables, accepted to ApJSubjects: Astrophysics (astro-ph)
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.
- [10] arXiv:0811.1999 [ps, pdf, other]
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Title: Energy-Dependent Speeds of Light for Cosmic-Ray ObservatoriesComments: 7 pages, comments solicitedSubjects: Astrophysics (astro-ph)
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.
- [11] arXiv:0811.2000 [ps, pdf, other]
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Title: Period-Luminosity Relations Derived from the OGLE-III Fundamental Mode CepheidsAuthors: C. Ngeow (UIUC), S. Kanbur (SUNY-Oswego), H. Neilson (U Toronto), A. Nanthakumar (SUNY-Oswego), J. Buonaccorsi (UMASS)Comments: 6 pages, 3 figures and 3 tables, ApJ acceptedSubjects: Astrophysics (astro-ph)
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.
- [12] arXiv:0811.2001 [ps, pdf, other]
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Title: Determining Quasar Black Hole Mass Functions from their Broad Emission Lines: Application to the Bright Quasar SurveyComments: 25 pages, 14 figures, emulate ApJ style, accepted by ApJSubjects: Astrophysics (astro-ph)
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).
- [13] arXiv:0811.2003 [ps, pdf, other]
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Title: On the (Non)Evolution of HI Disks over Cosmic TimeComments: 6 pages, 3 figures. Submitted to ApJL. Comments/criticism encouraged. See also this http URLSubjects: Astrophysics (astro-ph)
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.
- [14] arXiv:0811.2004 [ps, pdf, other]
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Title: Canny Algorithm, Cosmic Strings and the Cosmic Microwave BackgroundComments: 18 pp, 14 figuresSubjects: Astrophysics (astro-ph)
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.
- [15] arXiv:0811.2005 [ps, pdf, other]
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Title: Digital Access to a Sky Century at Harvard. II: Initial Photometry and AstrometryAuthors: S. Laycock (CfA/Gemini), S. Tang (CfA), J. Grindlay (CfA), E. Los (CfA), R. Simcoe (CfA), D. Mink (CfA)Comments: Submitted to AJ. 21 pages, 20 figures. See the DASCH project webpage: this http URL for high resolution figuresSubjects: Astrophysics (astro-ph)
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. - [16] arXiv:0811.2006 [pdf, other]
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Title: Structure of Neutron Stars in Tensor-Vector-Scalar TheoryComments: Accepted for publication in Phys. Rev. DSubjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc)
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.
- [17] arXiv:0811.2007 [pdf, other]
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Title: Magnetic fields and the location of the PDRAuthors: Gary J. FerlandJournal-ref: EAS Publications Series, Volume 31, 2008, pp.53-56Subjects: Astrophysics (astro-ph)
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.
- [18] arXiv:0811.2008 [ps, pdf, other]
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Title: Do the nearby BHB stars belong to the Thick Disk or the Halo?Authors: T. D. Kinman (1), Heather L. Morrison (2), Warren R. Brown (3) ((1) NOAO, (2) Case Western, (3) CfA)Comments: 14 pages, accepted to AJSubjects: Astrophysics (astro-ph)
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.
- [19] arXiv:0811.2014 [ps, pdf, other]
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Title: Predictions of Quasar Clustering: Redshift, Luminosity and Selection DependenceComments: 13 page, 7 figures. Accepted for publication in ApJSubjects: Astrophysics (astro-ph)
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.
- [20] arXiv:0811.2027 [ps, pdf, other]
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Title: PSR J1753-2240: A mildly recycled pulsar in an eccentric binary systemAuthors: M.J. Keith, M. Kramer, A.G. Lyne, R.P. Eatough, I.H. Stairs, A. Possenti, F. Camilo, R.N. ManchesterComments: For publication in MNRAS. 6 pages, 3 figuresSubjects: Astrophysics (astro-ph)
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.
- [21] arXiv:0811.2031 [ps, pdf, other]
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Title: Gravitational Radiation from Accreting Millisecond PulsarsComments: Proceedings of the 11th Marcel Grossmann Meeting on General Relativity, World Scientific 2008Subjects: Astrophysics (astro-ph)
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.
- [22] arXiv:0811.2033 [ps, pdf, other]
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Title: Higher order nonlinearity in accretion disks: QPOs of black hole and neutron star sources and their spinAuthors: Banibrata MukhopadhyayComments: 12 pages including 2 tables and 5 figures; accepted for publication in The Astrophysical JournalSubjects: Astrophysics (astro-ph)
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.
- [23] arXiv:0811.2034 [ps, pdf, other]
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Title: Transonic properties of the accretion disk around compact objectsAuthors: Banibrata MukhopadhyayComments: 12 pages including 3 figures; Proceedings of First Kodai-Trieste Workshop on Plasma Astrophysics, Kodaikanal Observatory, Indian Institute of Astrophysics, India, August 27 - September 7, 2007: Spinger (Astrophysics and Space Science Proceedings), eds. S. S. Hasan, V. Krishan, R. T. GangadharaSubjects: Astrophysics (astro-ph)
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.
- [24] arXiv:0811.2041 [ps, pdf, other]
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Title: The Stellar Populations of Lyman Break Galaxies at z~5Authors: Kiyoto Yabe, Kouji Ohta, Ikuru Iwata, Marcin Sawicki, Naoyuki Tamura, Masayuki Akiyama, Kentaro AokiComments: 29 pages, 21 figures, accepted for publication in ApJ. For high-resolution figures, see this http URLSubjects: Astrophysics (astro-ph)
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.
- [25] arXiv:0811.2053 [ps, pdf, other]
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Title: Physical properties of galaxies and their evolution in the VIMOS VLT Deep Survey. I. The evolution of the mass-metallicity relation up to z~0.9Authors: F. Lamareille (LATT, INAF), J. Brinchmann (CAUP), T. Contini (LATT), C.J. Walcher (LAM), S. Charlot (IAP), E. Pérez-Montero (LATT), G. Zamorani (INAF), L. Pozzetti (INAF), M. Bolzonella (INAF), B. Garilli, S. Paltani, A. Bongiorno (INAF), O. Le Fèvre (LAM), D. Bottini, V. Le Brun (LAM), D. Maccagni, R. Scaramella, M. Scodeggio, L. Tresse (LAM), G. Vettolani, A. Zanichelli, C. Adami (LAM), S. Arnouts (LAM), S. Bardelli (INAF), A. Cappi (INAF), P. Ciliegi (INAF), S. Foucaud, P. Franzetti, I. Gavignaud, L. Guzzo, O. Ilbert, A. Iovino, H.J. Mccracken (IAP), B. Marano, C. Marinoni, A. Mazure (LAM), B. Meneux, R. Merighi, R. Pellò (LATT), A. Pollo (LAM), M. Radovich, D. Vergani, E. Zucca (INAF), A. Romano, A. Grado, L. LimatolaComments: 21 pages, revised version submitted to A&ASubjects: Astrophysics (astro-ph)
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.
- [26] arXiv:0811.2058 [ps, pdf, other]
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Title: Structures, oscillations and solitons in large-scale multi-component self-gravitating systemsAuthors: Kinwah Wu (1), Ziri Younsi (1,2), Curtis J. Saxton (1) ((1) Mullard Space Science Laboratory, University College London, UK, (2) Department of Physics and Astronomy, University College London, UK)Comments: to appear in the proceedings of the Vulcano08 Workshop on "Frontier Objects in Astrophysics and Particle Physics"Subjects: Astrophysics (astro-ph)
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.
- [27] arXiv:0811.2060 [ps, pdf, other]
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Title: Radiative transfer in black hole systemsAuthors: Kinwah Wu (1), Warrick Ball (2), Steven V. Fuerst (3) ((1) Mullard Space Science Laboratory, University College London, UK, (2) Department of Physics and Astronomy, University College London, UK, (3) KIPAC, Stanford University, USA)Comments: to appear in the proceedings of the Vulcano08 Workshop on "Frontier Objects in Astrophysics and Particle Physics"Subjects: Astrophysics (astro-ph)
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.
- [28] arXiv:0811.2079 [ps, pdf, other]
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Title: Abundance Analysis of Barium StarsComments: 24 pages, 6 figures, accepted for publication in ChJAASubjects: Astrophysics (astro-ph)
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.
- [29] arXiv:0811.2085 [ps, pdf, other]
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Title: Physical properties of galaxies and their evolution in the VIMOS VLT Deep Survey. II. Extending the mass-metallicity relation to the range z=0.89-1.24Authors: E. Perez-Montero, T. Contini, F. Lamareille, J. Brinchmann, C. J. Walcher, S. Charlot, M. Bolzonella, L. Pozzetti, D. Bottini, B. Garilli, V. Le Brun, O. Le Fevre, D. Maccagni, R. Scaramella, M. Scodeggio, L. Tresse, G. Vettolani, A. Zanichelli, C. Adami, S. Arnouts, S. Bardelli, A. Cappi, P. Ciliegi, S. Foucaud, P.Franzetti, I. Gavignaud, L. Guzzo, O. Ilbert, A. Iovino, H.J. McCracken, B. Marano, C. Marinoni, A. Mazure, B. Meneux, R. Merighi, S. Paltani, R. Pello, A. Pollo, M. Radovich, D. Vergani, G. Zamorani, E. ZuccaComments: 9 pages and 8 figures. In press in Astronomy & AstrophysicsSubjects: Astrophysics (astro-ph)
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.
- [30] arXiv:0811.2095 [ps, pdf, other]
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Title: Observational Characteristics and Possible Asphericity of Over-Luminous Type Ia SupernovaeComments: 12 pages, 8 figures, 1 table. Accepted for publication in Monthly Notices of the Royal Astronomical SocietySubjects: Astrophysics (astro-ph)
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.
- [31] arXiv:0811.2100 [ps, pdf, other]
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Title: Simulation of a hybrid optical-radio-acoustic neutrino detector at the South PoleComments: 4 pages, 5 figures,1 Table, to appear in the proceedings of the Acoustic and Radio EeV Neutrino detection Activities (ARENA) 2008 conferenceSubjects: Astrophysics (astro-ph)
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.
- [32] arXiv:0811.2104 [pdf]
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Title: The Correlated Colors of Transneptunian BinariesComments: 28 pages, 4 figure, 4 tables. accepted to IcarusSubjects: Astrophysics (astro-ph)
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.
- [33] arXiv:0811.2115 [ps, pdf, other]
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Title: Searching for white dwarfs candidates in Sloan Digital Sky Survey DataAuthors: Mirosław Należyty (1), Agnieszka Majczyna (1,2), Anna Ciechanowska (1), Jerzy Madej (1) ((1) University of Warsaw Astronomical Observatory, Warsaw, Poland; (2) The Andrzej Sołtan Institute for Nuclear Studies, Warsaw, Poland)Comments: 4 pages, 3 figures; To appear in the proceedings of the EUROWD 08 conferenceSubjects: Astrophysics (astro-ph)
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.
- [34] arXiv:0811.2129 [pdf, other]
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Title: Tidally-induced thermonuclear SupernovaeComments: 8 pages, 2 figures, EuroWD08Subjects: Astrophysics (astro-ph)
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.
- [35] arXiv:0811.2130 [ps, pdf, other]
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Title: The flattening and the orbital structure of early-type galaxies and collisionless N-body binary disk mergersAuthors: J. Thomas, R. Jesseit, R. P. Saglia, R. Bender, A. Burkert, E. M. Corsini, K. Gebhardt, J. Magorrian, T. Naab, D. Thomas, G. WegnerComments: 14 pages, 8 figures; accepted for publication in MNRASSubjects: Astrophysics (astro-ph)
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.
- [36] arXiv:0811.2134 [ps, pdf, other]
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Title: Massive, red galaxies in a hierarchical universe I. Counts of Extremely Red Objects and basic propertiesComments: 20 pages, 16 figures, submitted to MNRAS; revised after referee's reportSubjects: Astrophysics (astro-ph)
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.
- [37] arXiv:0811.2142 [ps, pdf, other]
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Title: Submillimeter narrow emission lines from the inner envelope of IRC+10216Authors: Nimesh A. Patel (1), Ken H. Young (1), Sandra Brünken (1), Robert W. Wilson (1), Patrick Thaddeus (1), Karl M. Menten (2), Mark Reid (1), Michael C. McCarthy (1), Dinh-V-Trung (3), Carl A. Gottlieb (1), Abigail Hedden (1) ((1) Harvard-Smithsonian Center for Astrophysics, (2) Max Planck Institut für Radio Astronomie, (3) Academia Sinica Institute for Astronomy and Astrophysics)Comments: 5 pages, 5 figures, Accepted for publication in ApJSubjects: Astrophysics (astro-ph)
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.
- [38] arXiv:0811.2145 [ps, pdf, other]
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Title: Determining properties of the Antennae system - Merging ability for restricted N-bodyComments: To be published in EAS Publication Series (Proceedings of Symposium 7 of the JENAM 2008, Vienna). 4 pages, 2 figuresSubjects: Astrophysics (astro-ph)
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.
- [39] arXiv:0811.2148 [ps, pdf, other]
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Title: Extremely Red Objects in a hierarchical universeComments: 6 pages, 3 figures, To appear in the "Highlights of Spanish Astrophysics V " Proceedings of the VIII Scientific Meeting of the Spanish Astronomical Society (SEA) held in Santander, July 7-11, 2008Subjects: Astrophysics (astro-ph)
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.
- [40] arXiv:0811.2149 [ps, pdf, other]
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Title: Observational constraints of a Milne UniverseComments: Proceedings of the 43rd Rencontres de Moriond 2008Subjects: Astrophysics (astro-ph)
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.
- [41] arXiv:0811.2163 [ps, pdf, other]
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Title: An external-shock origin of the E_p-E_gamma relation for Gamma-Ray BurstsAuthors: A. PanaitescuComments: 6 pages, to appear in MNRASSubjects: Astrophysics (astro-ph)
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.
- [42] arXiv:0811.2176 [ps, pdf, other]
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Title: Non-Gaussian Signatures from the Post-inflationary Early UniverseComments: 4 pages, 4 figuresSubjects: Astrophysics (astro-ph)
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.
- [43] arXiv:0811.2199 [ps, pdf, other]
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Title: Reconstructing mass profiles of simulated galaxy clusters by combining Sunyaev-Zeldovich and X-ray imagesAuthors: S. Ameglio (1,2,3,4), S. Borgani (1,2,3), E. Pierpaoli (4), K. Dolag (5), S. Ettori (6,7), A. Morandi (8) ((1) Universita' di Trieste, (2) INFN-Trieste, (3) INAF-Trieste (4) University of Southern California, (5) Max-Planck-Institut fur Astrophysik, (6) INAF-Bologna, (7) INFN-Bologna, (8) Universita' di Bologna)Comments: 13 pages, 11 figures, submitted to MNRASSubjects: Astrophysics (astro-ph)
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.
- [44] arXiv:0811.2214 [ps, pdf, other]
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Title: The local FIR Galaxy Colour-Luminosity distribution: A reference for BLAST, and Herschel/SPIRE sub-mm surveysComments: 12 pages, 7 figures. Accepted by MNRASSubjects: Astrophysics (astro-ph)
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.
Cross-lists for Fri, 14 Nov 08
- [45] arXiv:0811.1548 (cross-list from gr-qc) [ps, pdf, other]
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Title: Thermodynamics of tidal charged black holesSubjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph); High Energy Physics - Theory (hep-th)
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.
- [46] arXiv:0811.1953 (cross-list from hep-ph) [ps, pdf, other]
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Title: Axino Dark Matter in Anomalous U(1)' ModelsComments: 14 pages, feynmfSubjects: High Energy Physics - Phenomenology (hep-ph); Astrophysics (astro-ph); High Energy Physics - Theory (hep-th)
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.
Replacements for Fri, 14 Nov 08
- [47] arXiv:0712.3939 (replaced) [ps, pdf, other]
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Title: Stable, Accelerating Universes in Modified GravityAuthors: Simon DeDeo (1), Dimitrios Psaltis (2) ((1) KICP, University of Chicago, (2) University of Arizona)Comments: 5 pages, 1 figure, matches published versionJournal-ref: Phys. Rev. D 78, 064013 (2008)Subjects: Astrophysics (astro-ph)
- [48] arXiv:0801.2950 (replaced) [ps, pdf, other]
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Title: Classical stability of a homogeneous, anisotropic inflating space-timeComments: 12 pages, no figures; references added, content in section V revised and some clarification made in text; minor typos corrected, v4 closely resembles version published in Phys. Rev. D; in v5 - incorrect argument in section V removed and one reference addedJournal-ref: Phys. Rev. D 77, 083510 (2008)Subjects: Astrophysics (astro-ph); High Energy Physics - Phenomenology (hep-ph)
- [49] arXiv:0805.0777 (replaced) [ps, pdf, other]
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Title: A Precise Estimate of the Radius of the Exoplanet HD 149026b from Spitzer PhotometryAuthors: Philip Nutzman, David Charbonneau, Joshua N. Winn, Heather A. Knutson, Jonathan J. Fortney, Matthew J. Holman, Eric AgolComments: 18 pages, 4 figures, accepted to ApJSubjects: Astrophysics (astro-ph)
- [50] arXiv:0807.1733 (replaced) [ps, pdf, other]
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Title: Nonlinear perturbation theory with halo bias and redshift-space distortions via the Lagrangian pictureAuthors: Takahiko MatsubaraComments: 19 pages, 10 figures. The expression <F^(n)> and Figs.1-5 in the published version are corrected (Erratum published). No qualitative changesJournal-ref: Phys. Rev. D 78, 083519 (2008); 78, 109901(E) (2008)Subjects: Astrophysics (astro-ph)
- [51] arXiv:0807.3447 (replaced) [ps, pdf, other]
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Title: The clustering of Ly-alpha emitters in a LambdaCDM UniverseAuthors: A. Orsi (1), C.G. Lacey (1), C.M. Baugh (1), L. Infante (2) ((1) ICC, Durham, (2) PUC, Chile)Comments: 17 pages, 18 figures. Accepted for publication in MNRAS. Minor revisions following referee's report. Replaced with version including Addendum to published paper discussing integral constraint correction. For high resolution figures see this http URLSubjects: Astrophysics (astro-ph)
- [52] arXiv:0807.3459 (replaced) [ps, pdf, other]
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Title: On Fermi acceleration and MHD-instabilities at ultra-relativistic magnetized shock wavesComments: 11 pages, 1 figure; to appear in MNRAS (minor changes)Subjects: Astrophysics (astro-ph)
- [53]