arXiv subjects

Avery Meiksin

Publications and source records attributed to Avery Meiksin.

At least 73 records · Page 4Linked to original sources

arXiv2004

The Small-scale Clustering of Luminous Red Galaxies via Cross-Correlation Techniques

We present the small-scale (0.2h^{-1} to 7h^{-1} Mpc) cross-correlations between 32,000 luminous early-type galaxies and a reference sample of 16 million normal galaxies from the Sloan Digital Sky Survey. Our method allows us to construct the spherically averaged, real-space cross-correlation function between the spectroscopic LRG sample and galaxies from the SDSS imaging. We report the cross-correlation as a function of scale, luminosity, and redshift. We find very strong luminosity dependences in the clustering amplitudes, up to a factor of 4 over a factor of 4 in luminosity, and measure this dependence with high signal-to-noise ratio. The luminosity dependence of bias is found to depend on scale, with more variation on smaller scales. The clustering as a function of scale is not a power law, but instead has a dip at 1h^{-1} Mpc and an excess on small scales. The fraction of red galaxies within the L* sample surrounding LRGs is a strong function of scale, as expected. However, the fraction of red galaxies evolves in redshift similarly on small and large scales, suggesting that cluster and field populations are changing in the same manner. The results highlight the advantage on small scales of using cross-correlation methods as a means of avoiding shot noise in samples of rare galaxies.

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arXiv2004

The Intermediate-Scale Clustering of Luminous Red Galaxies

We report the intermediate-scale (0.3 to 40 Mpc/h) clustering of 35,000 luminous early-type galaxies at redshifts 0.16 to 0.44 from the Sloan Digital Sky Survey. We present the redshift-space two-point correlation function ξ(s), the projected correlation function w_p(r_p), and the deprojected real-space correlation function ξ(r), for approximately volume-limited samples. As expected, the galaxies are highly clustered, with the correlation length varying from 9.8 +/- 0.2 Mpc/h to 11.2 +/- 0.2 Mpc/h, dependent on the specific luminosity range. For the -23.2 < Mg < -21.2 sample, the inferred bias relative to that of L* galaxies is 1.84 +/- 0.11 for 1 Mpc/h < r_p < 10 Mpc/h, with yet stronger clustering on smaller scales. We detect luminosity-dependent bias within the sample but see no evidence for redshift evolution between z=0.2 and z=0.4. We find a clear indication for deviations from a power-law in the real-space correlation function, with a dip at ~ 2 Mpc/h scales and an upturn on smaller scales. The precision measurements of these clustering trends offer new avenues for the study of the formation and evolution of these massive galaxies.

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arXiv2004

A library of high resolution Kurucz spectra in the wavelength range 3000 - 10000 AA

We present a library of 6410 synthetic spectra with resolution Lambda/dLambda = 250,000 based on the revised Kurucz 1993 model atmospheres. The library covers the wavelength range 3000 - 10,000 AA with 54 values of effective temperature in the range 5250 - 50,000 K, 11 values of log surface gravity between 0.0 and 5.0 and 19 metallicities in the range -5.0 to 1.0. We find that, with a few caveats, the library compares well with both the original 20 AA Kurucz spectra and also with observed spectra. The library is intended for use in population synthesis and physical parameterisation of stellar spectra. We assess the suitability of the library for these tasks.

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arXiv2004

Cosmological Parameters from Eigenmode Analysis of Sloan Digital Sky Survey Galaxy Redshifts

We present estimates of cosmological parameters from the application of the Karhunen-Loeve transform to the analysis of the 3D power spectrum of density fluctuations using Sloan Digital Sky Survey galaxy redshifts. We use Omega_m*h and f_b = Omega_b/Omega_m to describe the shape of the power spectrum, sigma8 for the (linearly extrapolated) normalization, and beta to parametrize linear theory redshift space distortions. On scales k < 0.16 h/Mpc, our maximum likelihood values are Omega_m*h = 0.264 +/-0.043, f_b = 0.286 +/- 0.065, sigma8 = 0.966 +/- 0.048, and beta = 0.45 +/- 0.12. When we take a prior on Omega_b from WMAP, we find Omega_m*h = 0.207 +/- 0.030, which is in excellent agreement with WMAP and 2dF. This indicates that we have reasonably measured the gross shape of the power spectrum but we have difficulty breaking the degeneracy between Omega_m*h and f_b because the baryon oscillations are not resolved in the current spectroscopic survey window function.

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arXiv2003

Radiative transfer through the Intergalactic Medium

We use a probabilistic method to compute the propagation of an ionization front corresponding to the re-ionization of the intergalactic medium in a LCDM cosmology, including both hydrogen and helium. The effects of radiative transfer substantially boost the temperature of the ionized gas over the case of uniform re-ionization. The resulting temperature-density relation of the ionized gas is both non-monotonic and multiple-valued, reflecting the non-local character of radiative transfer and suggesting that a single polytropic relation between local gas density and temperatue is a poor description of the thermodynamic state of baryons in the post-reionization universe.

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arXiv2003

The dependence on environment of the color-magnitude relation of galaxies

The distribution in color and absolute magnitude is presented for 55,158 galaxies taken from the Sloan Digital Sky Survey in the redshift range $0.08<z<0.12$, as a function of galaxy number overdensity in a line-of-sight cylinder of transverse radius $1 h^{-1} \mathrm{Mpc}$. In all environments, bulge-dominated galaxies (defined to be those with radial profiles best fit with large Sérsic indices) form a narrow, well defined color--magnitude relation. Although the most luminous galaxies reside preferentially in the highest density regions, there is only a barely detectable variation in the color (zero-point) or slope of the color--magnitude relation ($<0.02 \mathrm{mag}$ in $^{0.1}[g-r]$ or $[B-V]$). These results constrain variations with environmental density in the ages or metallicities of typical bulge-dominated galaxies to be under 20 percent.

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arXiv2003

The effects of UV background correlations on LyA forest flux statistics

We examine the possible effects of UV background fluctuations on the pixel flux power spectrum and auto-correlation function of the LyA forest due to a finite number of sources in an attenuating medium. We consider scenarios in which QSO sources dominate the contribution to the UV background. To estimate their contribution, we use the QSO luminosity functions from the 2dF and Sloan QSO surveys. We estimate self-consistent values for the attenuation length at the Lyman edge through the Intergalactic Medium using Particle Mesh simulations of the LyA forest, normalised by the measured mean LyA flux. We examine the convergence properties of the flux power spectrum and auto-correlation function under differing assumptions regarding pressure-smoothing. Convergence to better than 10% in the flux power spectrum at proper wavenumbers k < 0.015s/km requires a comoving resolution of 30-60kpc/h in a comoving box of size 25Mpc/h at z = 5, with the requirements becoming more severe at lower redshifts. We find much better covergence properties for the relative effects of the UV background fluctuations on the flux power spectrum. The background fluctuations increase the large-scale power and suppress the power at intermediate scales. At z < 4, the effect is only at the few percent level. By z > 5, however, the large-scale power is boosted by more than 50%, suggesting the flux power spectrum may serve as a useful tool for distinguishing QSO-dominated UV background scenarios from those dominated by galaxies.

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arXiv2003

Constraints on the UV metagalactic emissivity using the LyA forest

Numerical hydrodynamical simulations have proven a successful means of reproducing many of the statistical properties of the LyA forest as measured in high redshift (z > 4) quasar spectra. The source of ionization of the Intergalactic Medium (IGM), however, remains unknown. We investigate how the LyA forest may be used to probe the nature of the sources. We show that the attenuation of Lyman continuum photons by the IGM depends sensitively on the emissivity of the sources, permitting a strong constraint to be set on the required emissivity to match the measured values of the mean IGM LyA optical depth. We also investigate the effect of fluctuations in the UV background. We derive the distribution function of the background radiation field produced by discrete sources in an infinite universe, including the effects of attenuation by an intervening absorbing medium. We show that for z > 5, the fluctuations boost the mean LyA optical depth in a scenario in which QSO sources dominate the UV background. The fluctuations will also result in large spatial correlations in the ionization level of the IGM at high redshifts, providing a means of discriminating between scenarios in which stars and galaxies dominate the UV background vs a QSO-dominated background.

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arXiv2003

The Sloan Digital Sky Survey: The Cosmic Spectrum and Star-Formation History

We present a determination of the `Cosmic Optical Spectrum' of the Universe, i.e. the ensemble emission from galaxies, as determined from the red-selected Sloan Digital Sky Survey main galaxy sample and compare with previous results of the blue-selected 2dF Galaxy Redshift Survey. Broadly we find good agreement in both the spectrum and the derived star-formation histories. If we use a power-law star-formation history model where star-formation rate $\propto (1+z)^β$ out to z=1, then we find that $β$ of 2 to 3 is still the most likely model and there is no evidence for current surveys missing large amounts of star formation at high redshift. In particular `Fossil Cosmology' of the local universe gives measures of star-formation history which are consistent with direct observations at high redshift. Using the photometry of SDSS we are able to derive the cosmic spectrum in absolute units (i.e.$ W Å$^{-1}$ Mpc$^{-3}$) at 2--5Åresolution and find good agreement with published broad-band luminosity densities. For a Salpeter IMF the best fit stellar mass/light ratio is 3.7--7.5 $\Msun/\Lsun$ in the r-band (corresponding to $\omstars h = 0.0025$--0.0055) and from both the stellar emission history and the H$α$ luminosity density independently we find a cosmological star-formation rate of 0.03--0.04 h $\Msun$ yr$^{-1}$ Mpc$^{-3}$ today.

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arXiv2002

The Galaxy Luminosity Function and Luminosity Density at Redshift z=0.1

Using a catalog of 147,986 galaxy redshifts and fluxes from the Sloan Digital Sky Survey (SDSS) we measure the galaxy luminosity density at z=0.1 in five optical bandpasses corresponding to the SDSS bandpasses shifted to match their restframe shape at z=0.1. We denote the bands {0.1}{u}, {0.1}{g}, {0.1}{r}, {0.1}{i}, {0.1}{z}, with λ_{eff} = [3216, 4240, 5595, 6792, 8111] Angstroms respectively. We use a maximum likelihood method which allows for a general form for the shape of the luminosity function, simple luminosity and number evolution, incorporates flux uncertainties, and accounts for the flux limits of the survey. We find luminosity densities at z=0.1 in absolute AB magnitudes in a Mpc^3 of [-14.10 \pm 0.15, -15.18 \pm 0.03, -15.90 \pm 0.03, -16.24 \pm 0.03, -16.56 \pm 0.02] in [{0.1}{u}, {0.1}{g}, {0.1}{r}, {0.1}{i}, {0.1}{z}], respectively, using Ω_0 =0.3, Ω_Λ=0.7, and h=1, and using Petrosian magnitudes. Similar results are obtained using Sersic model magnitudes, suggesting that flux from outside the Petrosian apertures is not a major correction. In the {0.1}{r} band, the best fit Schechter function to our results has ϕ_\ast = (1.49 \pm 0.04) \times 10^{-2} h^3 Mpc^{-3}, M_\ast - 5\log_{10} h = -20.44 \pm 0.01, and α= -1.05\pm 0.01. In solar luminosities, the luminosity density in {0.1}{r} is (1.84 \pm 0.04) h 10^8 L_{{0.1}{r},\odot} Mpc^{-3}. Our results are consistent with other estimates of the luminosity density, from the Two-degree Field Galaxy Redshift Survey and the Millenium Galaxy Catalog. They represent a substantial change (\sim 0.5 mag) from earlier SDSS luminosity density results based on commissioning data, almost entirely because of the inclusion of evolution in the luminosity function model.

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arXiv2001

Higher Order Moments of the Angular Distribution of Galaxies from Early SDSS Data

We present initial results for counts in cells statistics of the angular distribution of galaxies in early data from the Sloan Digital Sky Survey (SDSS). We analyze a rectangular stripe $2.5^\circ$ wide, covering approximately 160 sq. degrees, containing over $10^6$ galaxies in the apparent magnitude range $18 < r^\prime < 22$, with areas of bad seeing, contamination from bright stars, ghosts, and high galactic extinction masked out. This survey region, which forms part of the SDSS Early Data Release, is the same as that for which two-point angular clustering statistics have recently been computed. The third and fourth moments of the cell counts, $s_3$ (skewness) and $s_4$ (kurtosis), constitute the most accurate measurements to date of these quantities (for $r^\prime < 21$) over angular scales $0.015^\circ-0.3^\circ$. They display the approximate hierarchical scaling expected from non-linear structure formation models and are in reasonable agreement with the predictions of $Λ$-dominated cold dark matter models with galaxy biasing that suppresses higher order correlations at small scales. The results are in general consistent with previous measurements in the APM, EDSGC, and Deeprange surveys. These results suggest that the SDSS imaging data are free of systematics to a high degree and will therefore enable determination of the skewness and kurtosis to 1% and less then 10%, as predicted by Colombi, Szapudi, & Szalay (1998).

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arXiv2001

KL Estimation of the Power Spectrum Parameters from the Angular Distribution of Galaxies in Early SDSS Data

We present measurements of parameters of the 3-dimensional power spectrum of galaxy clustering from 222 square degrees of early imaging data in the Sloan Digital Sky Survey. The projected galaxy distribution on the sky is expanded over a set of Karhunen-Loeve eigenfunctions, which optimize the signal-to-noise ratio in our analysis. A maximum likelihood analysis is used to estimate parameters that set the shape and amplitude of the 3-dimensional power spectrum. Our best estimates are Gamma=0.188 +/- 0.04 and sigma_8L = 0.915 +/- 0.06 (statistical errors only), for a flat Universe with a cosmological constant. We demonstrate that our measurements contain signal from scales at or beyond the peak of the 3D power spectrum. We discuss how the results scale with systematic uncertainties, like the radial selection function. We find that the central values satisfy the analytically estimated scaling relation. We have also explored the effects of evolutionary corrections, various truncations of the KL basis, seeing, sample size and limiting magnitude. We find that the impact of most of these uncertainties stay within the 2-sigma uncertainties of our fiducial result.

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arXiv1999

Radio Signatures of HI at High Redshift: Mapping the End of the ``Dark Ages''

The emission of 21-cm radiation from a neutral intergalactic medium (IGM) at high redshift is discussed in connection with the thermal and ionization history of the universe. The physical mechanisms that make such radiation detectable against the cosmic microwave background include Ly_alpha coupling of the hydrogen spin temperature to the kinetic temperature of the gas and preheating of the IGM by the first generation of stars and quasars. Three different signatures are investigated in detail: (a) the fluctuations in the redshifted 21-cm emission induced by the gas density inhomogeneities that develop at early times in cold dark matter (CDM) dominated cosmologies; (b) the sharp absorption feature in the radio sky due to the rapid rise of the Ly_alpha continuum background that marks the birth of the first UV sources in the universe; and (c) the 21-cm emission and absorption shells that are generated on several Mpc scales around the first bright quasars. Future radio observations with projected facilities like the Giant Metrewave Radio Telescope and the Square Kilometer Array may shed light on the power spectrum of density fluctuations at z>5, and map the end of the "dark ages", i.e. the transition from the post-recombination universe to one populated with radiation sources.

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arXiv1999

The First Light seen in the redshifted 21-cm radiation

We show how the investigation of the redshifted 21-cm radiation can give insight into the development of structures in the early universe (at redshifts z>5). In particular we investigate: the epoch of the first light; the fluctuations in the redshifted 21-cm emission induced by the density inhomogeneities in CDM dominated universes; the emission and absorption shells that are generated around the first bright quasars. Such features can be observed with the next generation radio facilities.

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arXiv1998

Simulating the Lyman Alpha Forest

In this paper we review the importance of the Lyman alpha forest as a probe of structure formation in the universe. We first discuss the statistics used to describe the Lyman alpha forest and the numerical techniques used to produce simulated spectra of the forest from a given cosmological model. We then discuss the physical picture of the absorbing structures that emerges from these numerical simulations. Finally, we comment on how two of the statistics, the slope of the column density distribution and the b parameter distribution, may be used to constrain competing cosmologies.

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arXiv1997

Physical Properties of the Lyman Alpha Forest in a Cold Dark Matter Cosmology

We discuss the origin and physical nature of the Lya forest absorption systems as found in hydrodynamical simulations of the Intergalactic Medium in a standard Cold Dark Matter cosmology (Omega=1, H0=50 km/s/Mpc, sigma_8=0.7). The structures of the systems that give rise to the Lya forest span a wide range in morphologies, depending on the density contrast. The absorption properties of the forest clouds correlate strongly with those of the underlying physical systems from which they arise. The highest column density systems (log N_HI > 15), correspond to highly overdense spheroidal structures, moderate column density systems (13 < log N_HI < 14), correspond to filaments, and the lowest density absorption systems originate from discrete fluctuations within underdense regions a few megaparsecs across, cosmic minivoids. Most of the intergalactic HeII opacity arises from these underdense regions. We are able to account for the distribution of optical depths in our synthesized spectra entirely by absorption due to discrete systems. We find that virtually all the baryons in the simulation fragment into structures that we can identify with discrete absorption lines, with at most 5% remaining in a smoothly distributed component (the Gunn-Peterson effect). We compare our results with the cloud ionization parameters inferred from Keck HIRES measurements of carbon and silicon in the Lya forest. Combining with constraints imposed by measurements of the mean intergalactic HI opacity, we find 0.03 < Omega_b < 0.08 and 0.3 < (Gamma_HI/ 10^-12 s^-1) < 1 at z=3-3.5.

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arXiv1997

Spectral Analysis of the Lyman Alpha Forest in a Cold Dark Matter Cosmology

We simulate the Lya forest in a standard CDM universe using a 2-level hierarchical grid code to evolve the dark and baryonic matter components self-consistently. We solve the time-dependent ionization equations for hydrogen and helium, adopting the Haardt & Madau (1996) estimate for the metagalactic UV radiation background. We compare our simulation results with the measured properties of the Lya forest by constructing synthetic spectra which we analyze in a manner similar to the method used by observers. The HI column density and Doppler parameter distributions we obtain agree closely with those measured by the Keck HIRES and earlier high spectral resolution observations over the column density range 10^{12} < NHI < 10^{16}. In particular, we find a power-law column density distribution persists to the lowest values reported from the HIRES measurements, in agreement with the incompleteness-corrected observations. We find evolution in the cloud number density and opacity comparable to the observed evolution. We also compare with measured values of the intergalactic HeII opacity. Our results require a HeII ionizing background lower than the Haardt & Madau estimate by a factor of 4, corresponding to a soft intrinsic QSO spectrum of alpha_Q = 1.8 - 2.

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arXiv1996

Cosmic Minivoids in the Intergalactic Medium

The Gunn-Peterson effect, absorption of Lya photons by a homogeneous component of the intergalactic medium (IGM), potentially provides a test of Big Bang Nucleosynthesis (BBN). With a lower limit on the UV radiation field estimated from the contribution due to QSOs, a measurement of the Lya opacity of the intergalactic medium would permit the derivation of a lower bound to the baryonic density of the universe. The effect, however, has continually eluded a convincing detection, both in HI and HeII, despite extensive searches. Recent cosmological hydrodynamical simulations of structure formation in the intergalactic medium suggest an explanation for its absence. In a Cold Dark Matter dominated cosmology, the fragmentation of the baryons is nearly complete, leaving a negligible remnant to comprise a smoothly distributed component. The fragmentation extends even into regions that are underdense, where it gives rise to most of the optically thin HI systems and nearly all of the HeII systems, both thin and saturated. The result is a Lya opacity from a smooth IGM that is suppressed by over two orders of magnitude from the BBN value.

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