Munch: Monday, February 25th, 2008
http://arxiv.org/PS_cache/arxiv/pdf/0802/0802.2715v1.pdf The Fate of the First Galaxies. III. Properties of Primordial Dwarf Galaxies and their Impact on the Intergalactic Medium(Submitted on 19 Feb 2008)
Abstract: In two previous papers, we presented simulations of the first galaxies in a representative volume of the Universe. The simulations are unique because we model feedback-regulated galaxy formation, using time-dependent, spatially-inhomogeneous radiative transfer coupled to hydrodynamics. Here, we study the properties of simulated primordial dwarf galaxies with masses <2x10^8 Msolar and investigate their impact on the intergalactic medium. While many primordial galaxies are dark, about 100--500 per comoving Mpc^3 are luminous but relatively faint. They form preferentially in chain structures, and have low surface brightness stellar spheroids extending to 20% of the virial radius. Their interstellar medium has mean density n_H~10--100 cm^-3, metallicity Z~ 0.01--0.1 Zsolar and can sustain a multi-phase structure. With large scatter, the mean efficiency of star formation scales with halo mass, <f_*> \propto M_dm^2, independent of redshift. Because of feedback, halos smaller than a critical mass, M_crit(z), are devoid of most of their baryons. More interestingly, we find that dark halos have always a smaller M_crit(z) than luminous ones. Metal enrichment of the intergalactic medium is inhomogeneous, with only a 1%--10% volume filling factor of enriched gas with [Z/H]>-3.0 and 10%--50% with [Z/H]>-5.0. At z=10, the fraction of stars with metallicity Z<10^-3 Zsolar is 10^-6 of the total stellar mass. Although detections of high-redshift dwarf galaxies with the James Webb Space Telescope will be a challenge, studies of their fossil records in the local Universe are promising because of their large spatial density. |
http://arxiv.org/PS_cache/arxiv/pdf/0802/0802.2416v1.pdf Self calibration of galaxy bias in spectroscopic redshift surveys of baryon acoustic oscillationsAuthors: Pengjie Zhang (SHAO)
(Submitted on 18 Feb 2008)
Abstract: Baryon acoustic oscillation (BAO) is a powerful probe on the expansion of the universe, shedding light on elusive dark energy and gravity at cosmological scales. BAO measurements through biased tracers of the underlying matter density field, as most proposals do, can reach high statistical accuracy. However, possible scale dependence in bias may induce non-negligible systematical errors, especially for the most ambitious spectroscopic surveys proposed. We show that precision spectroscopic redshift information available in these surveys allows for {\it self calibration} of the galaxy bias and its stochasticity, as function of scale and redshift. Through the effect of redshift distortion, one can simultaneously measure the real space power spectra of galaxies, galaxy-velocity and velocity, respectively. At relevant scales of BAO, galaxy velocity faithfully traces that of the underlying matter. This valuable feature enables a rather model independent way to measure the galaxy bias and its stochasticity by comparing the three power spectra. For the square kilometer array (SKA), this self calibration is statistically accurate to correct for 1% level shift in BAO peak positions induced by bias scale dependence. Furthermore, we find that SKA is able to detect BAO in the velocity power spectrum, opening a new window for BAO cosmology. |
http://arxiv.org/PS_cache/arxiv/pdf/0802/0802.2105v2.pdf The real-space clustering of luminous red galaxies around z<0.6 quasars in the Sloan Digital Sky Survey(Submitted on 14 Feb 2008 (v1), last revised 17 Feb 2008 (this version, v2))
Abstract: We measure the clustering of a sample of photometrically selected luminous red galaxies around a low redshift (0.2<z<0.6) sample of quasars selected from the Sloan Digital Sky Survey Data Release 5. We make use of a new statistical estimator to obtain precise measurements of the LRG auto-correlations and constrain halo occupation distributions for them. These are used to generate mock catalogs which aid in interpreting our quasar-LRG cross correlation measurements. The cross correlation is well described by a power law with slope 1.8\pm0.1 and r_0=6\pm0.5 h^{-1} Mpc, consistent with observed galaxy correlation functions. We find no evidence for `excess' clustering on 0.1 Mpc scales and demonstrate that this is consistent with the results of Serber et al (2006) and Strand et al (2007), when one accounts for several subtleties in the interpretation of their measurements. Combining the quasar-LRG cross correlation with the LRG auto-correlations, we determine a large-scale quasar bias b_QSO = 1.09\pm0.15 at a median redshift of 0.43, with no observed redshift or luminosity evolution. This corresponds to a mean halo mass <M>~ 10^{12} h^{-1} M_sun, Eddington ratios from 0.01 to 1 and lifetimes less than 10^{7} yr. Using simple models of halo occupation, these correspond to a number density of quasar hosts greater than 10^{-3} h^{3} Mpc^{-3} and stellar masses less than 10^{11} h^{-1} M_sun. The small-scale clustering signal can be interpreted with the aid of our mock LRG catalogs, and depends on the manner in which quasars inhabit halos. We find that our small scale measurements are inconsistent with quasar positions being randomly subsampled from halo centers above a mass threshold, requiring a satellite fraction > 25 per cent.
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http://arxiv.org/PS_cache/arxiv/pdf/0802/0802.2102v1.pdf Evolution of the 21 cm signal throughout cosmic historyAuthors: Jonathan R. Pritchard (CfA), Abraham Loeb (CfA)
(Submitted on 15 Feb 2008)
Abstract: The potential use of the redshifted 21 cm line from neutral hydrogen for probing the epoch of reionization is motivating the construction of several low-frequency interferometers. There is also much interest in the possibility of constraining the initial conditions from inflation and the nature of the dark matter and dark energy by probing the power-spectrum of density perturbations in three dimensions and on smaller scales than probed by the microwave background anisotropies. Theoretical understanding of the 21 cm signal has been fragmented into different regimes of physical interest. In this paper, we make the first attempt to describe the full redshift evolution of the 21 cm signal between 0<z<300. |
http://arxiv.org/ftp/arxiv/papers/0802/0802.2082.pdf Discovery of the progenitor of the type Ia supernova 2007onAuthors: Rasmus Voss, Gijs Nelemans
(Submitted on 14 Feb 2008)
Abstract: Type Ia supernovae are exploding stars that are used to measure the accelerated expansion of the Universe and are responsible for most of the iron ever produced. Although there is general agreement that the exploding star is a white dwarf in a binary system, the exact configuration and trigger of the explosion is unclear, which could hamper their use for precision cosmology. Two families of progenitor models have been proposed. In the first, a white dwarf accretes material from a companion until it exceeds the Chandrasekhar mass, collapses and explodes. Alternatively, two white dwarfs merge, again causing catastrophic collapse and an explosion. It has hitherto been impossible to determine if either model is correct. Here we report the discovery of an object in pre-supernova archival X-ray images at the position of the recent type Ia supernova (2007on) in the elliptical galaxy NGC 1404. Deep optical images (also archival) show no sign of this object. From this we conclude that the X-ray source is the progenitor of the supernova, which favours the accretion model for this supernova, although the host galaxy is older (6-9 Gyr) than the age at which the explosions are predicted in the accreting models.
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http://arxiv.org/PS_cache/arxiv/pdf/0802/0802.2041v1.pdf Dark Matter Accretion into Supermassive Black HolesAuthors: Sébastien Peirani (IAP), José Antonio De Freitas Pacheco (OCA)
(Submitted on 14 Feb 2008)
Abstract: The relativistic accretion rate of dark matter by a black hole is revisited. Under the assumption that the phase space density indicator, $Q=\rho_{\infty}/\sigma^3_{\infty}$, remains constant during the inflow, the derived accretion rate can be higher up to five orders of magnitude than the classical accretion formula, valid for non-relativistic and non-interacting particles, when typical dark halo conditions are considered. For these typical conditions, the critical point of the flow is located at distances of about 30-150 times the horizon radius. Application of our results to black hole seeds hosted by halos issued from cosmological simulations indicate that dark matter contributes to no more than ~10% of the total accreted mass, confirming that the bolometric quasar luminosity is related to the baryonic accretion history of the black hole. |
http://arxiv.org/PS_cache/arxiv/pdf/0802/0802.2506v1.pdf Discovery of a Very Bright Strongly-Lensed Galaxy Candidate at z ~ 7.6Authors: L. D. Bradley, R. J. Bouwens, H. C. Ford, G. D. Illingworth, M. J. Jee, N. Benitez, T. J. Broadhurst, M. Franx, B. L. Frye, L. Infante, V. Motta, P. Rosati, R. L. White, W. Zheng
(Submitted on 18 Feb 2008)
Abstract: Using HST and Spitzer IRAC imaging, we report the discovery of a very bright strongly-lensed Lyman break galaxy (LBG) candidate at z~7.6 in the field of the massive galaxy cluster Abell 1689. The galaxy candidate, which we refer to as A1689-zD1, shows a strong z-J break of at least 2.2 magnitudes and is completely undetected (<1 sigma) in HST/ACS g, r, i, and z data. These properties, combined with the very blue J-H and H-[4.5] colors, are exactly the properties of an z~7.6 LBG and can only be reasonably fit by a star-forming galaxy at z=7.6 +/- 0.4. Attempts to reproduce these properties with a model galaxy at z<4 yield particularly poor fits. A1689-zD1 has an observed (lensed) magnitude of 25.3 AB (8 sigma) in the NICMOS J band and is ~1.2 magnitudes brighter than the brightest-known z-dropout galaxy. When corrected for the cluster magnification of 9.3 at z~7.6, the candidate has an intrinsic magnitude of J=27.7 AB, or about an 0.3 L* galaxy at z~7.6. The source plane deprojection shows that the star formation is occurring in compact knots of size ~<300 pc. The best-fit stellar population synthesis models yield a median redshift of 7.6, stellar masses (1.6-3.9) x 10^9 M_sun, stellar ages 45-320 Myr, star-formation rates ~<7.6 M_sun/yr, and low reddening with A_V<0.3. These properties are generally similar to those of LBGs found at z~5-6. The inferred stellar ages suggest a formation redshift of z~8-10 (t~<0.63 Gyr). A1689-zD1 is the brightest observed, highly reliable z>7.0 galaxy candidate found to date.
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