Systematic Uncertainties in Stellar Mass Estimation for Distinct Galaxy Populations

We show that different stellar-mass estimation methods yield overall mass scales that disagree by factors up to ~2 for the z=0 galaxy population, and more importantly, relative mass scales that sometimes disagree by factors >~3 between distinct classes of galaxies (spiral/irregular types, classical E/S0s, and E/S0s whose colors reflect recent star formation). This comparison considers stellar mass estimates based on (a) two different calibrations of the correlation between K-band mass-to-light ratio and B-R color (Bell et al., Portinari et al.) and (b) detailed fitting of UBRJHK photometry and optical spectrophotometry using two different population synthesis models (Bruzual-Charlot, Maraston), with the same initial mass function in all cases. We also compare stellar+gas masses with dynamical masses. This analysis offers only weak arguments for preferring a particular stellar-mass estimation method, given the plausibility of real variations in dynamical properties and dark matter content. These results help to calibrate the systematic uncertainties inherent in mass-based evolutionary studies of galaxies, including comparisons of low and high redshift galaxies.Comment: 5 pages including 2 enlarged figures, ApJ Letters, accepte

Survey for Galaxies Associated with z~3 Damped Lyman alpha Systems I: Spectroscopic Calibration of u'BVRI Photometric Selection

We present a survey for z~3 Lyman break galaxies (LBGs) associated with damped Lyman alpha systems (DLAs) with the primary purpose of determining the DLA-LBG cross-correlation. This paper describes the acquisition and analysis of imaging and spectroscopic data of 9 quasar fields having 11 known z~3 DLAs covering an area of 465 arcmin^2. Using deep u'BVRI images, 796 LBG candidates to an apparent R_AB magnitude of 25.5 were photometrically selected from 17,343 sources detected in the field. Spectroscopic observations of 529 LBG candidates using Keck LRIS yielded 339 redshifts. We have conservatively identified 211 z>2 objects with =3.02+/-0.32. We discuss our method of z~3 LBG identification and present a model of the u'BVRI photometric selection function. We use the 339 spectra to evaluate our u'BVRI z~3 Lyman break photometric selection technique.Comment: 26 pages, 6 tables, 11 figures, accepted for publication in Ap

Constraining Primordial Non-Gaussianity With the Abundance of High Redshift Clusters

We show how observations of the evolution of the galaxy cluster number abundance can be used to constrain primordial non-Gaussianity in the universe. We carry out a maximum likelihood analysis incorporating a number of current datasets and accounting for a wide range of sources of systematic error. Under the assumption of Gaussianity, the current data prefer a universe with matter density $\Omega_m\simeq 0.3$ and are inconsistent with $\Omega_m=1$ at the $2\sigma$ level. If we assume $\Omega_m=1$, the predicted degree of cluster evolution is consistent with the data for non-Gaussian models where the primordial fluctuations have at least two times as many peaks of height $3\sigma$ or more as a Gaussian distribution does. These results are robust to almost all sources of systematic error considered: in particular, the $\Omega_m=1$ Gaussian case can only be reconciled with the data if a number of systematic effects conspire to modify the analysis in the right direction. Given an independent measurement of $\Omega_m$, the techniques described here represent a powerful tool with which to constrain non-Gaussianity in the primordial universe, independent of specific details of the non-Gaussian physics. We discuss the prospects and strategies for improving the constraints with future observations.Comment: Minor revisions to match published ApJ version, 14 pages emulateap

The Ucsd/Keck Damped Lya Abundance Database: A Decade of High Resolution Spectroscopy

We publish the Keck/HIRES and Keck/ESI spectra that we have obtained during the first 10 years of Keck observatory operations. Our full sample includes 42 HIRES spectra and 39 ESI spectra along 65 unique sightlines providing abundance measurements on ~85 damped Lya systems. The normalized data can be downloaded from the journal or from our supporting website: http://www.ucolick.org/~xavier/DLA/. The database includes all of the sightlines that have been included in our papers on the chemical abundances, kinematics, and metallicities of the damped Lya systems. This data has also been used to argue for variations in the fine-structure constant. We present new chemical abundance measurements for 10 damped Lya systems and a summary table of high-resolution metallicity measurements (including values from the literature) for 153 damped Lya systems at z>1.6. We caution, however, that this metallicity sample (and all previous ones) is biased to higher N(HI) values than a random sample.Comment: 55 pages, 11 figures. Accepted to ApJS. See http://www.ucolick.org/~xavier/DLA/ for the dat

Clustering of Intermediate Luminosity X-ray selected AGN at z~3

We present the first clustering results of X-ray selected AGN at z~3. Using Chandra X-ray imaging and UVR optical colors from MUSYC photometry in the ECDF-S field, we selected a sample of 58 z~3 AGN candidates. From the optical data we also selected 1385 LBG at 2.8<z< 3.8 with R<25.5. We performed auto-correlation and cross-correlation analyses, and here we present results for the clustering amplitudes and dark matter halo masses of each sample. For the LBG we find a correlation length of r_0,LBG = 6.7 +/- 0.5 Mpc, implying a bias value of 3.5 +/- 0.3 and dark matter (DM) halo masses of log(Mmin/Msun) = 11.8 +/- 0.1. The AGN-LBG cross-correlation yields r_0,AGN-LBG = 8.7 +/- 1.9 Mpc, implying for AGN at 2.8<z<3.8 a bias value of 5.5 +/- 2.0 and DM halo masses of log(Mmin/Msun) = 12.6 +0.5/-0.8. Evolution of dark matter halos in the Lambda CDM cosmology implies that today these z~3 AGN are found in high mass galaxies with a typical luminosity of 7+4/-2 L*.Comment: Accepted for publication in ApJ Letters. 4 pages, 4 figures (1 in color

The UCSD Radio-Selected Quasar Survey for Damped Lyman alpha System

As large optical quasar surveys for damped Lya become a reality and the study of star forming gas in the early Universe achieves statistical robustness, it is now vital to identify and quantify the sources of systematic error. Because the nature of optically-selected quasar surveys makes them vulnerable to dust obscuration, we have undertaken a radio-selected quasar survey for damped Lya systems to address this bias. We present the definition and results of this survey. We then combine our sample with the CORALS dataset to investigate the HI column density distribution function f(N) of damped Lya systems toward radio-selected quasars. We find that f(N) is well fit by a power-law f(N) = k_1 N^alpha_1, with log k_1 = 22.90 and alpha_1 = -2.18. This power-law is in excellent agreement with that of optically-selected samples at low N(HI), an important yet expected result given that obscuration should have negligible effect at these gas columns. However, because of the relatively small size of the radio-selected sample, 26 damped Lya systems in 119 quasars, f(N) is not well constrained at large N(HI) and the first moment of the HI distribution function, Omega_g, is, strictly speaking, a lower limit. The power-law is steep enough, however, that extrapolating it to higher column densities implies only a modest, logarithmic increase in Omega_g. The radio-selected value of Omega_g = 1.15 x 10^-3, agrees well with the results of optically-selected surveys. While our results indicate that dust obscuration is likely not a major issue for surveys of damped Lya systems, we estimate that a radio-selected sample of approximately 100 damped Lya systems will be required to obtain the precision necessary to absolutely confirm an absence of dust bias.Comment: 12 pages, 9 Figures. Accepted to ApJ April 11, 200

Contribution of Extragalactic Infrared Sources to CMB Foreground Anisotropy

We estimate the level of confusion to Cosmic Microwave Background anisotropy measurements caused by extragalactic infrared sources. CMB anisotropy observations at high resolution and high frequencies are especially sensitive to this foreground. We use data from the COBE satellite to generate a Galactic emission spectrum covering mm and sub-mm wavelengths. Using this spectrum as a template, we predict the microwave emission of the 5319 brightest infrared galaxies seen by IRAS. We simulate skymaps over the relevant range of frequencies (30-900 GHz) and instrument resolutions (10'-10 degrees Full Width Half Max). Analysis of the temperature anisotropy of these skymaps shows that a reasonable observational window is available for CMB anisotropy measurements.Comment: 14 pages (LaTex source), 3 PostScript figures. Final version, to appear in ApJLetters May 1. Expanded discussion of systematic error

Survey design for Spectral Energy Distribution fitting: a Fisher Matrix approach

The spectral energy distribution (SED) of a galaxy contains information on the galaxy's physical properties, and multi-wavelength observations are needed in order to measure these properties via SED fitting. In planning these surveys, optimization of the resources is essential. The Fisher Matrix formalism can be used to quickly determine the best possible experimental setup to achieve the desired constraints on the SED fitting parameters. However, because it relies on the assumption of a Gaussian likelihood function, it is in general less accurate than other slower techniques that reconstruct the probability distribution function (PDF) from the direct comparison between models and data. We compare the uncertainties on SED fitting parameters predicted by the Fisher Matrix to the ones obtained using the more thorough PDF fitting techniques. We use both simulated spectra and real data, and consider a large variety of target galaxies differing in redshift, mass, age, star formation history, dust content, and wavelength coverage. We find that the uncertainties reported by the two methods agree within a factor of two in the vast majority (~ 90%) of cases. If the age determination is uncertain, the top-hat prior in age used in PDF fitting to prevent each galaxy from being older than the Universe needs to be incorporated in the Fisher Matrix, at least approximately, before the two methods can be properly compared. We conclude that the Fisher Matrix is a useful tool for astronomical survey design.Comment: Accepted by ApJ; online Fisher Matrix tool available at http://galfish.physics.rutgers.ed

Spitzer Mid-to-Far-Infrared Flux Densities of Distant Galaxies

We study the infrared (IR) properties of high-redshift galaxies using deep Spitzer 24, 70, and 160 micron data. Our primary interest is to improve the constraints on the total IR luminosities, L(IR), of these galaxies. We combine the Spitzer data in the southern Extended Chandra Deep Field with a K-band-selected galaxy sample and photometric redshifts from the Multiwavelength Survey by Yale-Chile. We used a stacking analysis to measure the average 70 and 160 micron flux densities of 1.5 < z < 2.5 galaxies as a function of 24 micron flux density, X-ray activity, and rest-frame near-IR color. Galaxies with 1.5 < z < 2.5 and S(24)=53-250 micro-Jy have L(IR) derived from their average 24-160 micron flux densities within factors of 2-3 of those derived from the 24 micron flux densities only. However, L(IR) derived from the average 24-160 micron flux densities for galaxies with S(24) > 250 micro-Jy and 1.5 < z < 2.5 are lower than those derived using only the 24 micron flux density by factors of 2-10. Galaxies with S(24) > 250 micro-Jy have S(70)/S(24) flux ratios comparable to sources with X-ray detections or red rest-frame IR colors, suggesting that warm dust possibly heated by AGN may contribute to the high 24 micron emission. Based on the average 24-160 micron flux densities, nearly all 24 micron-selected galaxies at 1.5 < z < 2.5 have L(IR) < 6 x 10^12 solar luminosities, which if attributed to star formation corresponds to < 1000 solar masses per year. This suggests that high redshift galaxies may have similar star formation efficiencies and feedback processes as local analogs. Objects with L(IR) > 6 x 10^12 solar luminosities are quite rare, with a surface density ~ 30 +/- 10 per sq. deg, corresponding to ~ 2 +/- 1 x 10^-6 Mpc^-3 over 1.5 < z < 2.5.Comment: Accepted for Publication in ApJ. AASTeX format. 34 pages, 12 figures. Updated references and other small textual revision