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We present the Cardinal mock galaxy catalogs, a new version of the Buzzard simulation that has been updated to support ongoing and future cosmological surveys, including DES, DESI, and LSST. These catalogs are based on a one-quarter sky simulation populated with galaxies out to a redshift of $z=2.35$ to a depth of $m_{\rm{r}}=27$. Compared to the Buzzard mocks, the Cardinal mocks include an updated subhalo abundance matching (SHAM) model that considers orphan galaxies and includes mass-dependent scatter between galaxy luminosity and halo properties. This model can simultaneously fit galaxy clustering and group--galaxy cross-correlations measured in three different luminosity threshold samples. The Cardinal mocks also feature a new color assignment model that can simultaneously fit color-dependent galaxy clustering in three different luminosity bins. We have developed an algorithm that uses photometric data to improve the color assignment model further and have also developed a novel method to improve small-scale lensing below the ray-tracing resolution. These improvements enable the Cardinal mocks to accurately reproduce the abundance of galaxy clusters and the properties of lens galaxies in the Dark Energy Survey data. As such, these simulations will be a valuable tool for future cosmological analyses based on large sky surveys. The cardinal mock will be released upon publication at https://chunhaoto.com/cardinalsim., Comment: 37 pages; 20 figures. See figure 1 for summary and appendix K for a list of main differences between Cardinal and Buzzard. To be submitted to APJ; Comments welcome. Highlights can be found at https://chunhaoto.com/cardinalsim

Dramatic recent progress in understanding galactic chemical evolution (GCE) has been driven partly by direct observations of the distant past with HST and JWST of stellar abundances from giant high-resolution spectroscopic surveys (APOGEE, GALAH) and the complementary power of Gaia astrometry and photometry. Focusing on archaeology, I give a rapid-fire, and I hope synthesizing, review of work my collaborators and I have done on theoretical modeling and observational interpretation. I discuss (1) the interleaved but distinguishable roles of stellar scale astrophysics and galactic scale astrophysics in governing GCE, (2) the use of abundance ratio trends to empirically infer nucleosynthetic yields, (3) the uncertainty in the overall scale of yields and its degeneracy with the importance of galactic outflows, (4) the emergence of equilibrium in GCE, (5) the dimensionality of the stellar distribution in chemical abundance space, and (6) insights from chemical abundances on the early history of the Milky Way, including measurements of the intrinsic scatter of abundance ratios in metal-poor stars (-2 < [Fe/H] < -1), suggesting that a typical halo star at this metallicity is enriched by the products of $N \sim 50$ supernovae mixed over $\sim 10^5 M_\odot$ of star-forming gas., 10 pp. running lightly over a lot of ground. Proceedings of IAU Symposium 377, Early Disk-Galaxy Formation: From JWST to the Milky Way, eds. F. Tabatabaei, B. Barbuy, and Y. Ting. Reactions welcome!

We use chemistry ([alpha/Fe] and [Fe/H]), main sequence turnoff ages, and kinematics determined from H3 Survey spectroscopy and Gaia astrometry to identify the birth of the Galactic disk. We separate in-situ and accreted stars on the basis of angular momenta and eccentricities. The sequence of high-alpha in-situ stars persists down to at least [Fe/H]=-2.5 and shows unexpected non-monotonic behavior: with increasing metallicity the population first declines in [alpha/Fe], then increases over the range -1.3, Comment: 13 pages, 10 figures, submitted to ApJ

Surface abundances of C, N, and O in red giants are affected by processed material mixed into the stars' convective envelopes. Using a sample of $\sim 5100$ stars with elemental abundances from APOGEE and asteroseismic masses from {\it Kepler}, we test theoretical stellar models that predict this mixing, then apply these models to derive birth C, N, and O abundances for these stars. Our models with standard mixing can reproduce the observed trends to within plausible uncertainties in the birth abundances. Some models with ''extra'' mixing processes fail, predicting trends with surface gravity or evolutionary state that are not observed. Applying mixing corrections to the APOGEE abundances removes the observed age-dependence of log(N/O) and log(C/N), but it leaves trends of log(N/O) and log(C/N) with metallicity, as expected based on nucleosynthesis models. The stellar N/O trend agrees well with Dopita et al.'s calibration of gas phase log(N/O) with metallicity, and with gas phase trends in the MaNGA integral field survey of nearby galaxies. We also find a substantial separation in birth [N/Mg] ratios between high-[$\alpha$/Fe] (''thick disc'') stars and low-[$\alpha$/Fe] (''thin disc'') stars. We find a smaller but still clear separation for [C/Mg]. The trends of birth C and N abundances with [Fe/H] and [$\alpha$/Fe] could affect spectroscopic age estimates for red giants that rely on the observed C/N ratio as a diagnostic of stellar mass., Comment: 18 pages, 12 figures

Using a sample of red giant stars from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) Data Release 16, we infer the conditional distribution $p([��/\text{Fe}]\,|\,[\text{Fe/H}])$ in the Milky Way disk for the $��$-elements Mg, O, Si, S, and Ca. In each bin of [Fe/H] and Galactocentric radius $R$, we model $p([��/\text{Fe}])$ as a sum of two Gaussians, representing "low-$��$" and "high-$��$" populations with scale heights $z_1=0.45\,\text{kpc}$ and $z_2=0.95\,\text{kpc}$, respectively. By accounting for age-dependent and $z$-dependent selection effects in APOGEE, we infer the [$��$/Fe] distributions that would be found for a fair sample of long-lived stars covering all $z$. Near the Solar circle, this distribution is bimodal at sub-solar [Fe/H], with the low-$��$ and high-$��$ peaks clearly separated by a minimum at intermediate [$��$/Fe]. In agreement with previous results, we find that the high-$��$ population is more prominent at smaller $R$, lower [Fe/H], and larger $|z|$, and that the sequence separation is smaller for Si and Ca than for Mg, O, and S. We find significant intrinsic scatter in [$��$/Fe] at fixed [Fe/H] for both the low-$��$ and high-$��$ populations, typically $\sim 0.04$-dex. The means, dispersions, and relative amplitudes of this two-Gaussian description, and the dependence of these parameters on $R$, [Fe/H], and $��$-element, provide a quantitative target for chemical evolution models and a test for hydrodynamic simulations of disk galaxy formation. We argue that explaining the observed bimodality will probably require one or more sharp transitions in the disk's gas accretion, star formation, or outflow history in addition to radial mixing of stellar populations., Accepted for publication in MNRAS

We explore synergies between the space-based Wide-Field Infrared Survey Telescope (WFIRST) and the ground-based Rubin Observatory Legacy Survey of Space and Time (LSST). In particular, we consider a scenario where the currently envisioned survey strategy for WFIRST's High Latitude Survey (HLS), i.e., 2000 square degrees in four narrow photometric bands is altered in favor of a strategy that combines rapid coverage of the LSST area (to full LSST depth) in one band. We find that a 5-month WFIRST survey in the W-band can cover the full LSST survey area providing high-resolution imaging for >95% of the LSST Year 10 gold galaxy sample. We explore a second, more ambitious scenario where WFIRST spends 1.5 years covering the LSST area. For this second scenario we quantify the constraining power on dark energy equation of state parameters from a joint weak lensing and galaxy clustering analysis, and compare it to an LSST-only survey and to the Reference WFIRST HLS survey. Our survey simulations are based on the WFIRST exposure time calculator and redshift distributions from the CANDELS catalog. Our statistical uncertainties account for higher-order correlations of the density field, and we include a wide range of systematic effects, such as uncertainties in shape and redshift measurements, and modeling uncertainties of astrophysical systematics, such as galaxy bias, intrinsic galaxy alignment, and baryonic physics. Assuming the 5-month WFIRST wide scenario, we find a significant increase in constraining power for the joint LSST+WFIRST wide survey compared to LSST Y10 (FoM(Wwide)= 2.4 FoM(LSST)) and compared to LSST+WFIRST HLS (FoM(Wwide)= 5.5 FoM(HLS))., added references, comments welcome

We have used flux-transmission correlations in Lyα forests to measure the imprint of baryon acoustic oscillations (BAO). The study uses spectra of 157 783 quasars in the redshift range 2:1 ≤ z ≤ 3:5 from the Sloan Digital Sky Survey (SDSS) data release 12 (DR12). Besides the statistical improvements on our previous studies using SDSS DR9 and DR11, we have implemented numerous improvements in the analysis procedure, allowing us to construct a physical model of the correlation function and to investigate potential systematic errors in the determination of the BAO peak position. The Hubble distance, DH = c=H(z), relative to the sound horizon is DH(z = 2:33)=rd = 9:07 ± 0:31. The best-determined combination of comoving angular-diameter distance, DM, and the Hubble distance is found to be D0:7 H D0:3 M =rd = 13:94±0:35. This value is 1:028±0:026 times the prediction of the flat-ΛCDM model consistent with the cosmic microwave background (CMB) anisotropy spectrum. The errors include marginalization over the effects of unidentified high-density absorption systems and fluctuations in ultraviolet ionizing radiation. Independently of the CMB measurements, the combination of our results and other BAO observations determine the open-ΛCDM density parameters to be ΩM = 0:296 ± 0:029, ΩΛ = 0:699 ± 0:100 and Ωk = -0:002 ± 0:119.

We present a measurement of baryon acoustic oscillations (BAO) in the cross-correlation of quasars with the Ly$��$-forest flux-transmission at a mean redshift $z=2.40$. The measurement uses the complete SDSS-III data sample: 168,889 forests and 234,367 quasars from the SDSS Data Release DR12. In addition to the statistical improvement on our previous study using DR11, we have implemented numerous improvements at the analysis level allowing a more accurate measurement of this cross-correlation. We also developed the first simulations of the cross-correlation allowing us to test different aspects of our data analysis and to search for potential systematic errors in the determination of the BAO peak position. We measure the two ratios $D_{H}(z=2.40)/r_{d} = 9.01 \pm 0.36$ and $D_{M}(z=2.40)/r_{d} = 35.7 \pm 1.7$, where the errors include marginalization over the non-linear velocity of quasars and the metal - quasar cross-correlation contribution, among other effects. These results are within $1.8��$ of the prediction of the flat-$��$CDM model describing the observed CMB anisotropies. We combine this study with the Ly$��$-forest auto-correlation function [2017A&A...603A..12B], yielding $D_{H}(z=2.40)/r_{d} = 8.94 \pm 0.22$ and $D_{M}(z=2.40)/r_{d} = 36.6 \pm 1.2$, within $2.3��$ of the same flat-$��$CDM model., accepted by A&A

SDSS-V will be an all-sky, multi-epoch spectroscopic survey of over six million objects. It is designed to decode the history of the Milky Way, trace the emergence of the chemical elements, reveal the inner workings of stars, and investigate the origin of planets. It will also create an integral-field spectroscopic map of the gas in the Galaxy and the Local Group that is 1,000x larger than the current state of the art and at high enough spatial resolution to reveal the self-regulation mechanisms of galactic ecosystems. SDSS-V will pioneer systematic, spectroscopic monitoring across the whole sky, revealing changes on timescales from 20 minutes to 20 years. The survey will thus track the flickers, flares, and radical transformations of the most luminous persistent objects in the universe: massive black holes growing at the centers of galaxies. The scope and flexibility of SDSS-V will be unique among extant and future spectroscopic surveys: it is all-sky, with matched survey infrastructures in both hemispheres; it provides near-IR and optical multi-object fiber spectroscopy that is rapidly reconfigurable to serve high target densities, targets of opportunity, and time-domain monitoring; and it provides optical, ultra-wide-field integral field spectroscopy. SDSS-V, with its programs anticipated to start in 2020, will be well-timed to multiply the scientific output from major space missions (e.g., TESS, Gaia, eROSITA) and ground-based projects. SDSS-V builds on the 25-year heritage of SDSS's advances in data analysis, collaboration infrastructure, and product deliverables. The project is now refining its science scope, optimizing the survey strategies, and developing new hardware that builds on the SDSS-IV infrastructure. We present here an overview of the current state of these developments as we seek to build our worldwide consortium of institutional and individual members., Comment: 23-page summary of the current status of SDSS-V. See also http://www.sdss.org/future/. SDSS-V is currently seeking institutional and individual members -- join us!

We present a tentative detection of the large-scale structure of Ly α emission in the Universe at redshifts z = 2-3.5 by measuring the cross-correlation of Ly α surface brightness with quasars in Sloan Digital Sky Survey/Baryon Oscillation Spectroscopic Survey.We use amillion spectra targeting luminous red galaxies at z < 0.8, after subtracting a best-fitting model galaxy spectrum from each one, as an estimate of the high-redshift Ly α surface brightness. The quasar- Ly α emission cross-correlation is detected on scales 1 ~ 15 h-1 Mpc, with shape consistent with a Λ (CDM model with) Ωm = 0.30+0.10-0.07. The predicted amplitude of this cross-correlation is proportional to the product of the mean Ly α surface brightness, (μα), the amplitude of mass fluctuations and the quasar and Ly α emission bias factors. We infer (μα) (bα/3) = (3.9 ± 0.9) × 10-21 erg s-1 cm-2 Å-1 arcsec-2, where bα is the Ly α emission bias. If star-forming galaxies dominate this emission, we find ρSFR = (0.28 ± 0.07)(3/bα) yr-1 Mpc-3. For bα = 3, this value is~30 times larger than previous estimates from individually detected Ly α emitters, but consistent with the total ρSFR derived from dust-corrected, continuum UV galaxy surveys, if most of the Ly α photons from these galaxies avoid dust absorption and are reemitted after diffusing in large gas haloes. Heating of intergalactic gas by He II photoionization from quasar radiation or jets may alternatively explain the detected correlation, and cooling radiation from gas in galactic haloes may also contribute. We also detect redshift space anisotropy of the quasar-Ly α emission cross-correlation, finding evidence at the 3.0σ level that it is radially elongated, which may be explained by radiative-transfer effects. Our measurements represent the first application of the intensity mapping technique to optical observations.

We derive constraints on cosmological parameters and tests of dark energy models from the combination of baryon acoustic oscillation (BAO) measurements with cosmic microwave background (CMB) and Type Ia supernova (SN) data. We take advantage of high-precision BAO measurements from galaxy clustering and the Ly-alpha forest (LyaF) in the BOSS survey of SDSS-III. BAO data alone yield a high confidence detection of dark energy, and in combination with the CMB angular acoustic scale they further imply a nearly flat universe. Combining BAO and SN data into an "inverse distance ladder" yields a 1.7% measurement of $H_0=67.3 \pm1.1$ km/s/Mpc. This measurement assumes standard pre-recombination physics but is insensitive to assumptions about dark energy or space curvature, so agreement with CMB-based estimates that assume a flat LCDM cosmology is an important corroboration of this minimal cosmological model. For open LCDM, our BAO+SN+CMB combination yields $\Omega_m=0.301 \pm 0.008$ and curvature $\Omega_k=-0.003 \pm 0.003$. When we allow more general forms of evolving dark energy, the BAO+SN+CMB parameter constraints remain consistent with flat LCDM. While the overall $\chi^2$ of model fits is satisfactory, the LyaF BAO measurements are in moderate (2-2.5 sigma) tension with model predictions. Models with early dark energy that tracks the dominant energy component at high redshifts remain consistent with our constraints. Expansion history alone yields an upper limit of 0.56 eV on the summed mass of neutrino species, improving to 0.26 eV if we include Planck CMB lensing. Standard dark energy models constrained by our data predict a level of matter clustering that is high compared to most, but not all, observational estimates. (Abridged), Comment: 38 pages, 20 figures, BOSS collaboration paper; v2: fixed inconsistent definitions of DH, added references; v3: version accepted by PRD, corrected error resulting in significantly weaker constraints on decaying dark matter model

We use the Ly-$��$ Mass Association Scheme (LyMAS; Peirani et al. 2014) to predict cross-correlations at $z=2.5$ between dark matter halos and transmitted flux in the Ly-$��$ forest, and compare to cross-correlations measured for quasars and damped Ly-$��$ systems (DLAs) from the Baryon Oscillation Spectroscopic Survey (BOSS) by Font-Ribera et al. (2012, 2013). We calibrate LyMAS using Horizon-AGN hydrodynamical cosmological simulations of a $(100\ h^{-1}\ \mathrm{Mpc})^3$ comoving volume. We apply this calibration to a $(1\ h^{-1}\ \mathrm{Gpc})^3$ simulation realized with $2048^3$ dark matter particles. In the 100 $h^{-1}$ Mpc box, LyMAS reproduces the halo-flux correlations computed from the full hydrodynamic gas distribution very well. In the 1 $h^{-1}$ Gpc box, the amplitude of the large scale cross-correlation tracks the halo bias $b_h$ as expected. We provide empirical fitting functions that describe our numerical results. In the transverse separation bins used for the BOSS analyses, LyMAS cross-correlation predictions follow linear theory accurately down to small scales. Fitting the BOSS measurements requires inclusion of random velocity errors; we find best-fit RMS velocity errors of 399 km s$^{-1}$ and 252 km s$^{-1}$ for quasars and DLAs, respectively. We infer bias-weighted mean halo masses of $M_h/10^{12}\ h^{-1}M_\odot=2.19^{+0.16}_{-0.15}$ and $0.69^{+0.16}_{-0.14}$ for the host halos of quasars and DLAs, with $\sim 0.2$ dex systematic uncertainty associated with redshift evolution, IGM parameters, and selection of data fitting range., Accepted by MNRAS, 23 pages, 20 figures. For a short video summarizing this paper, please visit: https://youtu.be/9ghGNtF16JA

The Ly$\alpha$ forest transmission probability distribution function (PDF) is an established probe of the intergalactic medium (IGM) astrophysics, especially the temperature-density relationship of the IGM. We measure the transmission PDF from 3393 Baryon Oscillations Spectroscopic Survey (BOSS) quasars from SDSS Data Release 9, and compare with mock spectra that include careful modeling of the noise, continuum, and astrophysical uncertainties. The BOSS transmission PDFs, measured at $\langle z \rangle = [2.3,2.6,3.0]$, are compared with PDFs created from mock spectra drawn from a suite of hydrodynamical simulations that sample the IGM temperature-density relationship, $\gamma$, and temperature at mean-density, $T_0$, where $T(\Delta) = T_0 \Delta^{\gamma-1}$. We find that a significant population of partial Lyman-limit systems with a column-density distribution slope of $\beta_\mathrm{pLLS} \sim -2$ are required to explain the data at the low-transmission end of transmission PDF, while uncertainties in the mean Ly$\alpha$ forest transmission affect the high-transmission end. After modelling the LLSs and marginalizing over mean-transmission uncertainties, we find that $\gamma=1.6$ best describes the data over our entire redshift range, although constraints on $T_0$ are affected by systematic uncertainties. Within our model framework, isothermal or inverted temperature-density relationships ($\gamma \leq 1$) are disfavored at a significance of over 4$\sigma$, although this could be somewhat weakened by cosmological and astrophysical uncertainties that we did not model., Comment: Accepted for publication in ApJ. 35 pages, 25 figures

We examine the star formation histories (SFHs) of galaxies in smoothed particle hydrodynamics (SPH) simulations, compare them to parametric models that are commonly used in fitting observed galaxy spectral energy distributions, and examine the efficacy of these parametric models as practical tools for recovering the physical parameters of galaxies. The commonly used tau-model, with SFR ~ exp(-t/tau), provides a poor match to the SFH of our SPH galaxies, with a mismatch between early and late star formation that leads to systematic errors in predicting colours and stellar mass-to-light ratios. A one-parameter lin-exp model, with SFR ~ t*exp(-t/tau), is much more successful on average, but it fails to match the late-time behavior of the bluest, most actively star-forming galaxies and the passive, "red and dead" galaxies. We introduce a 4-parameter model, which transitions from lin-exp to a linear ramp after a transition time, which describes our simulated galaxies very well. We test the ability of these parametrised models to recover (at z=0, 0.5, and 1) the stellar mass-to-light ratios, specific star formation rates, and stellar population ages from the galaxy colours, computed from the full SPH star formation histories using the FSPS code of Conroy et al. (2009). Fits with tau-models systematically overestimate M/L by ~ 0.2 dex, overestimate population ages by ~ 1-2 Gyr, and underestimate sSFR by ~ 0.05 dex. Fits with lin-exp are less biased on average, but the 4-parameter model yields the best results for the full range of galaxies. Marginalizing over the free parameters of the 4-parameter model leads to slightly larger statistical errors than 1-parameter fits but essentially removes all systematic biases, so this is our recommended procedure for fitting real galaxies., Comment: 28 pages, 18 figures

We report a detection of the baryon acoustic oscillation (BAO) feature in the flux-correlation function of the Ly�� forest of high-redshift quasars with a statistical significance of five standard deviations. The study uses 137,562 quasars in the redshift range $2.1\le z \le 3.5$ from the Data Release 11 (DR11) of the Baryon Oscillation Spectroscopic Survey (BOSS) of SDSS-III. This sample contains three times the number of quasars used in previous studies. The measured position of the BAO peak determines the angular distance, $D_A(z=2.34)$ and expansion rate, $H(z=2.34)$, both on a scale set by the sound horizon at the drag epoch, $r_d$. We find $D_A/r_d=11.28\pm0.65(1��)^{+2.8}_{-1.2}(2��)$ and $D_H/r_d=9.18\pm0.28(1��)\pm0.6(2��)$ where $D_H=c/H$. The optimal combination, $\sim D_H^{0.7}D_A^{0.3}/r_d$ is determined with a precision of $\sim2\%$. For the value $r_d=147.4~{\rm Mpc}$, consistent with the CMB power spectrum measured by Planck, we find $D_A(z=2.34)=1662\pm96(1��)~{\rm Mpc}$ and $H(z=2.34)=222\pm7(1��)~{\rm km\,s^{-1}Mpc^{-1}}$. Tests with mock catalogs and variations of our analysis procedure have revealed no systematic uncertainties comparable to our statistical errors. Our results agree with the previously reported BAO measurement at the same redshift using the quasar-Ly�� forest cross-correlation. The auto-correlation and cross-correlation approaches are complementary because of the quite different impact of redshift-space distortion on the two measurements. The combined constraints from the two correlation functions imply values of $D_A/r_d$ and $D_H/r_d$ that are, respectively, 7% low and 7% high compared to the predictions of a flat $��$CDM cosmological model with the best-fit Planck parameters. With our estimated statistical errors, the significance of this discrepancy is $\approx 2.5��$., Accepted for publication in A&A. 17 pages, 18 figures

We present measurements of the anisotropic galaxy clustering from the Data Release 9 (DR9) CMASS sample of the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). We analyze the broad-range shape of the monopole and quadrupole correlation functions to obtain constraints, at the effective redshift $z=0.57$ of the sample, on the Hubble expansion rate $H(z)$, the angular-diameter distance $D_A(z)$, the normalized growth rate $f(z)\sigma_8(z)$, the physical matter density $\Omega_m h^2$, and the biased amplitude of matter fluctuation b\sigma_8(z). We obtain {$H(0.57)$, $D_A(0.57)$, $f(0.57)\sigma_8(0.57)$, $\Omega_m h^2$, $b\sigma_8(0.57)$} = {$87.6_{-6.8}^{+6.7}$, $1396\pm73$, $0.126_{-0.010}^{+0.008}$, $1.19\pm0.14$, $0.428\pm0.066$} and their covariance matrix as well. The parameters which are not well constrained by our of galaxy clustering analysis are marginalized over with wide flat priors. Since no priors from other data sets (i.e., CMB) are adopted and no dark energy models are assumed, our results from BOSS CMASS galaxy clustering alone may be combined with other data sets, i.e. CMB, SNe, lensing or other galaxy clustering data to constrain the parameters of a given cosmological model. We show that the major power on constraining dark energy from the anisotropic galaxy clustering signal, as compared to the angular-averaged one (monopole), arises from including the normalized growth rate $f(z)\sigma_8(z)$. In the case of the wCDM cosmological model our single-probe CMASS constraints, combined with CMB (WMAP9+SPT), yield a value for the dark energy equation of state parameter of $w=-0.90\pm0.11$. Therefore, it is important to include $f(z)\sigma_8(z)$ while investigating the nature of dark energy with current and upcoming large-scale galaxy surveys., Comment: 13 pages, 6 figures; it matches the accepted version by MNRAS

How do observed voids relate to the underlying dark matter distribution? To examine the spatial distribution of dark matter contained within voids identified in galaxy surveys, we apply Halo Occupation Distribution models representing sparsely and densely sampled galaxy surveys to a high-resolution N-body simulation. We compare these galaxy voids to voids found in the halo distribution, low-resolution dark matter, and high-resolution dark matter. We find that voids at all scales in densely sampled surveys - and medium- to large-scale voids in sparse surveys - trace the same underdensities as dark matter, but they are larger in radius by ~20%, they have somewhat shallower density profiles, and they have centers offset by ~0.4Rv rms. However, in void-to-void comparison we find that shape estimators are less robust to sampling, and the largest voids in sparsely sampled surveys suffer fragmentation at their edges. We find that voids in galaxy surveys always correspond to underdensities in the dark matter, though the centers may be offset. When this offset is taken into account, we recover almost identical radial density profiles between galaxies and dark matter. All mock catalogs used in this work are available at http://www.cosmicvoids.net., Comment: 12 pages, 8 figures, minor changes, MNRAS accepted

We describe fitting methods developed to analyze fluctuations in the Lyman-�� forest and measure the parameters of baryon acoustic oscillations (BAO). We apply our methods to BOSS Data Release 9. Our method is based on models of the three-dimensional correlation function in physical coordinate space, and includes the effects of redshift-space distortions, anisotropic non-linear broadening, and broadband distortions. We allow for independent scale factors along and perpendicular to the line of sight to minimize the dependence on our assumed fiducial cosmology and to obtain separate measurements of the BAO angular and relative velocity scales. Our fitting software and the input files needed to reproduce our main BOSS Data Release 9 results are publicly available., Submitted to JCAP, 38 pages, 26 figures

We report a detection of the baryon acoustic oscillation (BAO) feature in the three-dimensional correlation function of the transmitted flux fraction in the \Lya forest of high-redshift quasars. The study uses 48,640 quasars in the redshift range $2.1\le z \le 3.5$ from the Baryon Oscillation Spectroscopic Survey (BOSS) of the third generation of the Sloan Digital Sky Survey (SDSS-III). At a mean redshift $z=2.3$, we measure the monopole and quadrupole components of the correlation function for separations in the range $20\hMpc, accepted for publication in Astronomy and Astrophysics

We present the BOSS Lyman-alpha (Lya) Forest Sample from SDSS Data Release 9, comprising 54,468 quasar spectra with zqso > 2.15 suitable for Lya forest analysis. This data set probes the intergalactic medium with absorption redshifts 2.0 < z_alpha < 5.7 over an area of 3275 square degrees, and encompasses an approximate comoving volume of 20 h^-3 Gpc^3. With each spectrum, we have included several products designed to aid in Lya forest analysis: improved sky masks that flag pixels where data may be unreliable, corrections for known biases in the pipeline estimated noise, masks for the cores of damped Lya systems and corrections for their wings, and estimates of the unabsorbed continua so that the observed flux can be converted to a fractional transmission. The continua are derived using a principal component fit to the quasar spectrum redwards of restframe Lya (lambda > 1216 Ang), extrapolated into the forest region and normalized by a linear function to fit the expected evolution of the Lya forest mean-flux. The estimated continuum errors are ~5% rms. We also discuss possible systematics arising from uncertain spectrophotometry and artifacts in the flux calibration; global corrections for the latter are provided. Our sample provides a convenient starting point for users to analyze clustering in BOSS Lya forest data, and it provides a fiducial data set that can be used to compare results from different analyses of baryon acoustic oscillations in the Lya forest. The full data set is available from the SDSS-III DR9 web site., 15 pages, 11 figures; Submitted to AJ

Recently Menard et al. detected a subtle but systematic change in the mean color of quasars as a function of their projected separation from foreground galaxies, extending to comoving separations of ~10Mpc/h, which they interpret as a signature of reddening by intergalactic dust. We present theoretical models of this remarkable observation, using SPH cosmological simulations of a (50Mpc/h)^3 volume. Our primary model uses a simulation with galactic winds and assumes that dust traces the intergalactic metals. The predicted galaxy-dust correlation function is similar in form to the galaxy-mass correlation function, and reproducing the MSFR data requires a dust-to-metal mass ratio of 0.24, about half the value in the Galactic ISM. Roughly half of the reddening arises in dust that is more than 100Kpc/h from the nearest massive galaxy. We also examine a simulation with no galactic winds, which predicts a much smaller fraction of intergalactic metals (3% vs. 35%) and therefore requires an unphysical dust-to-metal ratio of 2.18 to reproduce the MSFR data. In both models, the signal is dominated by sightlines with E(g-i)=0.001-0.1. The no-wind simulation can be reconciled with the data if we also allow reddening to arise in galaxies up to several x 10^10 Msun. The wind model predicts a mean visual extinction of A_V ~0.0133 mag out to z=0.5, with a sightline-to-sightline dispersion similar to the mean, which could be significant for future supernova cosmology studies. Reproducing the MSFR results in these simulations requires that a large fraction of ISM dust survive its expulsion from galaxies and its residence in the intergalactic medium. Future observational studies that provide higher precision and measure the dependence on galaxy type and environment will allow detailed tests for models of enriched galactic outflows and the survival of IG dust., Comment: Matches version accepted by MNRAS

Since 2004, I have been collaborating with artist Josiah McElheny on the design of cosmological sculptures, inspired originally by the chandeliers of the Metropolitan Opera House in New York. The four works that we have completed to date have appeared in galleries and museums in the United States, England, and Spain. In this article, I describe the history of the project and offer some conclusions about collaborations between scientists and artists. A companion article presents the scientific background of the sculptures in greater depth., Comment: To appear in the journal Narrative, as a contribution to the proceedings of the symposium Narrative, Science, and Performance, ed. J. Phelan. Further information and higher resolution images are available at http://www.astronomy.ohio-state.edu/~dhw/McElheny

We compare the properties of galaxies that form in a cosmological simulation without strong feedback to observations at z=0. We confirm previous findings that models without strong feedback overproduce the observed galaxy baryonic mass function, especially at the low and high mass extremes. Through post-processing we investigate what kinds of feedback would be required to reproduce observed galaxy masses and star formation rates. To mimic an extreme form of "preventive" feedback (e.g., AGN radio mode) we remove all baryonic mass that was originally accreted via "hot mode" from shock-heated gas. This does not bring the high mass end of the galaxy mass function into agreement with observations because much of the stellar mass in these systems formed at high redshift from baryons that originally accreted via "cold mode" onto lower mass progenitors. An efficient "ejective" feedback mechanism, such as supernova driven winds, must reduce the masses of these progenitors. Feedback must also reduce the masses of lower mass z=0 galaxies, which assemble at lower redshifts and have much lower star formation rates. If we monotonically re-map galaxy masses to reproduce the observed mass function, but retain the simulation's predicted star formation rates, we obtain fairly good agreement with the observed sequence of star-forming galaxies but fail to recover the observed population of passive, low star formation rate galaxies. Suppressing all hot mode accretion improves agreement for high mass galaxies but worsens the agreement at intermediate masses. Reproducing these z=0 observations requires a feedback mechanism that dramatically suppresses star formation in a fraction of galaxies, increasing with mass, while leaving star formation rates of other galaxies essentially unchanged., MNRAS in press. 15 pages, 5 figures, minimal changes from the first version

We use the abundance and weak lensing mass measurements of the SDSS maxBCG cluster catalog to simultaneously constrain cosmology and the richness--mass relation of the clusters. Assuming a flat \LambdaCDM cosmology, we find \sigma_8(\Omega_m/0.25)^{0.41} = 0.832\pm 0.033 after marginalization over all systematics. In common with previous studies, our error budget is dominated by systematic uncertainties, the primary two being the absolute mass scale of the weak lensing masses of the maxBCG clusters, and uncertainty in the scatter of the richness--mass relation. Our constraints are fully consistent with the WMAP five-year data, and in a joint analysis we find \sigma_8=0.807\pm 0.020 and \Omega_m=0.265\pm 0.016, an improvement of nearly a factor of two relative to WMAP5 alone. Our results are also in excellent agreement with and comparable in precision to the latest cosmological constraints from X-ray cluster abundances. The remarkable consistency among these results demonstrates that cluster abundance constraints are not only tight but also robust, and highlight the power of optically-selected cluster samples to produce precision constraints on cosmological parameters., Comment: comments welcome

We present measurements of the quasar two-point correlation function, ��_{Q}, over the redshift range z=0.3-2.2 based upon data from the SDSS. Using a homogeneous sample of 30,239 quasars with spectroscopic redshifts from the DR5 Quasar Catalogue, our study represents the largest sample used for this type of investigation to date. With this redshift range and an areal coverage of approx 4,000 deg^2, we sample over 25 h^-3 Gpc^3 (comoving) assuming the current LCDM cosmology. Over this redshift range, we find that the redshift-space correlation function, xi(s), is adequately fit by a single power-law, with s_{0}=5.95+/-0.45 h^-1 Mpc and ��_{s}=1.16+0.11-0.16 when fit over s=1-25 h^-1 Mpc. Using the projected correlation function we calculate the real-space correlation length, r_{0}=5.45+0.35-0.45 h^-1 Mpc and ��=1.90+0.04-0.03, over scales of rp=1-130 h^-1 Mpc. Dividing the sample into redshift slices, we find very little, if any, evidence for the evolution of quasar clustering, with the redshift-space correlation length staying roughly constant at s_{0} ~ 6-7 h^-1 Mpc at z, 28 pages, 26 figures, ApJ accepted. Online materials (including source code, catalogues and high-resolution figures) can be found at http://www.astro.psu.edu/users/npr/DR5/

This paper describes the Sixth Data Release of the Sloan Digital Sky Survey. With this data release, the imaging of the northern Galactic cap is now complete. The survey contains images and parameters of roughly 287 million objects over 9583 deg², including scans over a large range of Galactic latitudes and longitudes. The survey also includes 1.27 million spectra of stars, galaxies, quasars, and blank sky (for sky subtraction) selected over 7425 deg². This release includes much more stellar spectroscopy than was available in previous data releases and also includes detailed estimates of stellar temperatures, gravities, and metallicities. The results of improved photometric calibration are now available, with uncertainties of roughly 1% in g, r, i, and z, and 2% in u, substantially better than the uncertainties in previous data releases. The spectra in this data release have improved wavelength and flux calibration, especially in the extreme blue and extreme red, leading to the qualitatively better determination of stellar types and radial velocities. The spectrophotometric fluxes are now tied to point-spread function magnitudes of stars rather than fiber magnitudes. This gives more robust results in the presence of seeing variations, but also implies a change in the spectrophotometric scale, which is now brighter by roughly 0.35 mag. Systematic errors in the velocity dispersions of galaxies have been fixed, and the results of two independent codes for determining spectral classifications and redshifts are made available. Additional spectral outputs are made available, including calibrated spectra from individual 15 minute exposures and the sky spectrum subtracted from each exposure. We also quantify a recently recognized underestimation of the brightnesses of galaxies of large angular extent due to poor sky subtraction; the bias can exceed 0.2 mag for galaxies brighter than r = 14 mag.

We study the formation of galaxies in a (50 Mpc/h)^3 cosmological simulation (2x288^3 particles), evolved using the entropy conserving SPH code Gadget-2. Most of the baryonic mass in galaxies of all masses is originally acquired through filamentary "cold mode" accretion of gas that was never shock heated to its halo virial temperature, confirming the key feature of our earlier results obtained with a different SPH code (Keres et al. 2005). Atmospheres of hot, virialized gas develop in halos above ~2.5e11 Msun, a transition mass that is nearly constant from z=3 to z=0. Cold accretion persists in halos above the transition mass, especially at z>=2. It dominates the growth of galaxies in low mass halos at all times, and it is the main driver of the cosmic star formation history. Satellite galaxies have accretion rates similar to central galaxies of the same baryonic mass at high redshifts, but they have less accretion than comparable central galaxies at low redshift. Relative to our earlier results, the Gadget-2 simulations predict much lower rates of "hot mode" accretion from the virialized gas component of massive halos. At z, MNRAS in press, 24 pages, 11 figures. Minor changes and updated references. A copy with high resolution figures (Highly Recommended) can be found at http://www.cfa.harvard.edu/~dkeres/coldmode/ms_keres_rv1.ps.gz

We present a Fourier analysis of the clustering of galaxies in the combined Main galaxy and Luminous Red Galaxy (LRG) Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) sample. The aim of our analysis is to consider how well we can measure the cosmological matter density using the signature of the horizon at matter-radiation equality embedded in the large-scale power spectrum. The new data constrains the power spectrum on scales 100--600h^-1Mpc with significantly higher precision than previous analyses of just the SDSS Main galaxies, due to our larger sample and the inclusion of the LRGs. This improvement means that we can now reveal a discrepancy between the shape of the measured power and linear CDM models on scales 0.01, Comment: 21 pages, 19 figures, minor corrections to match version accepted by ApJ

In a large scale view of the universe, galaxies are the basic unit of structure. A typical bright galaxy may contain 100 billion stars and span tens of thousands of light years, but the empty expanses between the galaxies are much larger still. Galaxies are not randomly distributed in space, but instead reside in groups and clusters, which are themselves arranged in an intricate lattice of filaments and walls, threaded by tunnels and pocked with bubbles. Two ambitious new surveys, the Two-Degree Field Galaxy Redshift Survey (2dFGRS) and the Sloan Digital Sky Survey (SDSS), have mapped the three-dimensional distribution of galaxies over an unprecedented range of scales. Astronomers are using these maps to learn about conditions in the early universe, the matter and energy contents of the cosmos, and the physics of galaxy formation., Comment: 4 pages, 1 figure. A brief, semi-popular review of large scale structure studies with the 2dFGRS and the SDSS

This paper describes the Third Data Release of the Sloan Digital Sky Survey (SDSS). This release, containing data taken up through 2003 June, includes imaging data in five bands over 5282 deg², photometric and astrometric catalogs of the 141 million objects detected in these imaging data, and spectra of 528,640 objects selected over 4188 deg². The pipelines analyzing both images and spectroscopy are unchanged from those used in our Second Data Release.

The ability to test the nature of dark mass-energy components in the universe through large-scale structure studies hinges on accurate predictions of sky survey expectations within a given world model. Numerical simulations predict key survey signatures with varying degrees of confidence, limited mainly by the complex astrophysics of galaxy formation. As surveys grow in size and scale, systematic uncertainties in theoretical modeling can become dominant. Dark energy studies will challenge the computational cosmology community to critically assess current techniques, develop new approaches to maximize accuracy, and establish new tools and practices to efficiently employ globally networked computing resources., Comment: 5 pages, theory white paper submitted to the Dark Energy Task Force

We study the distribution of Eddington luminosity ratios, L_bol/L_edd, of active galactic nuclei (AGNs) discovered in the AGN and Galaxy Evolution Survey (AGES). We combine H-beta, MgII, and CIV line widths with continuum luminosities to estimate black hole (BH) masses in 407 AGNs, covering the redshift range z~0.3-4 and the bolometric luminosity range L_bol~10^45-10^47 erg/s. The sample consists of X-ray or mid-infrared (24 micron) point sources with optical magnitude R, 34 pages including 12 figures. Incorporates referee's comments. Accepted for publication in ApJ

We measure the power spectrum, P_F(k,z), of the transmitted flux in the Ly-alpha forest using 3035 high redshift quasar spectra from the Sloan Digital Sky Survey. This sample is almost two orders of magnitude larger than any previously available data set, yielding statistical errors of ~0.6% and ~0.005 on, respectively, the overall amplitude and logarithmic slope of P_F(k,z). This unprecedented statistical power requires a correspondingly careful analysis of the data and of possible systematic contaminations in it. For this purpose we reanalyze the raw spectra to make use of information not preserved by the standard pipeline. We investigate the details of the noise in the data, resolution of the spectrograph, sky subtraction, quasar continuum, and metal absorption. We find that background sources such as metals contribute significantly to the total power and have to be subtracted properly. We also find clear evidence for SiIII correlations with the Ly-alpha forest and suggest a simple model to account for this contribution to the power. While it is likely that our newly developed analysis technique does not eliminate all systematic errors in the P_F(k,z) measurement below the level of the statistical errors, our tests indicate that any residual systematics in the analysis are unlikely to affect the inference of cosmological parameters from P_F(k,z). These results should provide an essential ingredient for all future attempts to constrain modeling of structure formation, cosmological parameters, and theories for the origin of primordial fluctuations., Comment: 92 pages, 45 of them figures, submitted to ApJ, data available at http://feynman.princeton.edu/~pmcdonal/LyaF/sdss.html

The Sloan Digital Sky Survey (SDSS) has validated and made publicly available its Second Data Release. This data release consists of 3324 deg² of five-band (ugriz) imaging data with photometry for over 88 million unique objects, 367,360 spectra of galaxies, quasars, stars, and calibrating blank sky patches selected over 2627 deg² of this area, and tables of measured parameters from these data. The imaging data reach a depth of r ≈ 22.2 (95% completeness limit for point sources) and are photometrically and astrometrically calibrated to 2% rms and 100 mas rms per coordinate, respectively. The imaging data have all been processed through a new version of the SDSS imaging pipeline, in which the most important improvement since the last data release is fixing an error in the model fits to each object. The result is that model magnitudes are now a good proxy for point-spread function magnitudes for point sources, and Petrosian magnitudes for extended sources. The spectroscopy extends from 3800 to 9200 Å at a resolution of 2000. The spectroscopic software now repairs a systematic error in the radial velocities of certain types of stars and has substantially improved spectrophotometry. All data included in the SDSS Early Data Release and First Data Release are reprocessed with the improved pipelines and included in the Second Data Release. Further characteristics of the data are described, as are the data products themselves and the tools for accessing them.

We examine the temperature history of gas accreted by forming galaxies in SPH simulations. About half the gas shock heats to roughly the virial temperature of the galaxy potential well before cooling, condensing, and forming stars, but the other half radiates its acquired gravitational energy at much lower temperatures, typically T, 1 figure added, Appendix discussing SAMs added, some text changes. Matches the version accepted by MNRAS. 31 pages (MNRAS style), 21 figures,For high resolution version of the paper (highly recommended) follow http://www.astro.umass.edu/~keres/paper/ms2.ps.gz

Not the way one might have thought. In hydrodynamic simulations of galaxy formation, some gas follows the traditionally envisioned route, shock heating to the halo virial temperature before cooling to the much lower temperature of the neutral ISM. But most gas enters galaxies without ever heating close to the virial temperature, gaining thermal energy from weak shocks and adiabatic compression, and radiating it just as quickly. This ``cold mode'' accretion is channeled along filaments, while the conventional, ``hot mode'' accretion is quasi-spherical. Cold mode accretion dominates high redshift growth by a substantial factor, while at z, 7 pages, 1 figure. To be published in the proceedings of the IGM/Galaxy Connection- The Distribution of Baryons at z=0 conference

We use hydrodynamic simulations to predict correlations between Lya forest absorption and galaxies at redshift z~3. The probability distribution function (PDF) of Lya flux decrements shifts systematically towards higher values in the vicinity of galaxies, reflecting the overdense environments in which these galaxies reside. The predicted signal remains strong in spectra smoothed over 50-200 km/s, allowing tests with moderate resolution quasar spectra. The strong bias of high redshift galaxies towards high density regions imprints a clear signature on the flux PDF, but the predictions are not sensitive to galaxy baryon mass or star formation rate, and they are similar for galaxies and for dark matter halos. The dependence of the flux PDF on galaxy proximity is sensitive to redshift determination errors, with rms errors of 150-300 km/s substantially weakening the predicted trends. On larger scales, the mean galaxy overdensity in a cube of 5 or 10 Mpc/h (comoving) is strongly correlated with the mean Lya flux decrement on a line of sight through the cube center. The slope of the correlation is ~3 times steeper for galaxies than for dark matter as a result of galaxy bias. The predicted large scale correlation is in qualitative agreement with recently reported observational results. However, observations also show a drop in absorption in the immediate vicinity of galaxies, which our models do not predict even if we allow the galaxies or AGNs within them to be ionizing sources. This decreased absorption could be a signature of galaxy feedback on the surrounding IGM, perhaps via galactic winds. Peculiar velocities often allow gas at comoving distances ~1.5 Mpc/h to produce saturated absorption at the galaxy redshift, so any feedback mechanism must suppress neutral hydrogen out to these radii to match the data. (Abridged), Comment: 54 pages, 19 figures. Accepted for publication in ApJ. Includes discussion of simple wind models

I review recent SDSS results related to galaxies and large scale structure, including: (1) discovery of coherent, unbound structures in the stellar halo, (2) demonstration that Pal 5 has tidal tails and Draco doesn't, (3) precise measurement of the galaxy luminosity function and its variation with surface brightness, color, and morphology, (4) detailed examination of the Fundamental Plane of 9000 early type galaxies, (5) measurement, via galaxy-galaxy lensing, of the extended dark matter distributions around galaxies and their variation with luminosity, morphology, and environment, (6) measurement of galaxy angular clustering, spatial clustering and velocity dispersion as a function of luminosity and color. I then discuss what we can hope to learn in the long run from galaxy clustering in the SDSS and the 2dFGRS. Galaxy clustering depends on the dark halo population and on the Halo Occupation Distribution (HOD), which specifies the way that galaxies populate the halos. SPH simulations and semi-analytic models make similar predictions for the probability P(N|M) that a halo of virial mass M contains N galaxies of a specified type: a non-linear mean occupation N_avg(M), sub-Poisson fluctuations about the mean in low mass halos, and strong dependence of N_avg(M) on stellar population age. The complementary sensitivity of different clustering statistics should make it possible to determine the HOD empirically given an assumed cosmological model. Furthermore, changes to the cosmological model change the halo population in ways that would be difficult to mask by changing the HOD. Ultimately, we can hope to have our cake and eat it too, obtaining strong guidance to the physics of galaxy formation by deriving the HOD of different classes of galaxies, while simultaneously carrying out precision tests of cosmological models., Comment: 16 pp, 1 fig, to appear in A New Era In Cosmology, eds. T. Shanks & N. Metcalfe, ASP Conference Series

Using a hydrodynamic simulation of a LCDM universe, we investigate the "X-ray forest" absorption imprinted on the spectra of background quasars by the intervening intergalactic medium (IGM). In agreement with previous studies, we find that OVII and OVIII produce the strongest absorption features. The strong oxygen absorbers that might be detectable with Chandra or XMM-Newton arise in gas with T ~ 10^6 K and overdensities delta >~ 100 that are characteristic of galaxy groups. Future X-ray missions could detect weaker oxygen absorption produced by gas with a wider range of temperatures and the lower densities of unvirialized structures; they could also detect X-ray forest absorption by C, N, Ne, Fe, and possibly Si. If the IGM metallicity is 0.1 solar, then the predicted number of systems strong enough for a ~5\sigma detection with Chandra or XMM-Newton is extremely low, though scatter in metallicity would increase the number of strong absorbers even if the mean metallicity remained the same. Our simulation reproduces the high observed incidence of OVI absorbers (in the UV), and the most promising strategy for finding the X-ray forest is to search at the redshifts of known OVI systems, thus reducing the signal-to-noise threshold required for a significant detection. However, while many OVI absorbers have associated OVII or OVIII absorption, the OVI systems trace only the low temperature phases of the X-ray forest, and a full accounting of the strong OVII and OVIII systems will require a mission with the anticipated capabilities of Constellation-X. The large effective area of the XEUS satellite would make it an extremely powerful instrument for studying the IGM, measuring X-ray forest absorption by a variety of elements and revealing the shock-heated filaments that may be an important reservoir of cosmic baryons., Comment: 41 pages including 16 figures, replaced with version accepted by ApJ. Includes clarification of several points and brief discussion of recent observational results

We present Chandra observations that provide the most direct evidence to date for the pervasive, moderate density, shock-heated intergalactic medium predicted by leading cosmological scenarios. We also comment briefly on future observations with Constellation-X., Comment: To be published in the proceedings of the conference "IGM/Galaxy Connection- The Distribution of Baryons at z=0". 6 pages

We study the predicted sub-mm emission from massive galaxies in a Lambda-CDM universe, using hydrodynamic cosmological simulations. Assuming that most of the emission from newly formed stars is absorbed and reradiated in the rest-frame far-IR, we calculate the number of galaxies that would be detected in sub-mm surveys conducted with SCUBA. The predicted number counts are strongly dependent on the assumed dust temperature and emissivity law. With plausible choices for SED parameters (e.g., T=35 K, beta=1.0), the simulation predictions reproduce the observed number counts above ~ 1 mJy. The sources have a broad redshift distribution with median z ~ 2, in reasonable agreement with observational constraints. However, the predicted count distribution may be too steep at the faint end, and the fraction of low redshift objects may be larger than observed. In this physical model of the sub-mm galaxy population, the objects detected in existing surveys consist mainly of massive galaxies (several M_*) forming stars fairly steadily over timescales ~ 10^8-10^9 years, at moderate rates ~100 Msun/yr. The typical descendants of these sub-mm sources are even more massive galaxies, with old stellar populations, found primarily in dense environments. While the resolution of our simulations is not sufficient to determine galaxy morphologies, these properties support the proposed identification of sub-mm sources with massive ellipticals in the process of formation. The most robust and distinctive prediction of this model, stemming directly from the long timescale and correspondingly moderate rate of star formation, is that the far-IR SEDs of SCUBA sources have a relative high 850 micron luminosity for a given bolometric luminosity. [Abridged], Comment: Submitted to ApJ. 34 pages including 8 PS figures

We present the first measurements of clustering in the Sloan Digital Sky Survey (SDSS) galaxy redshift survey. Our sample consists of 29,300 galaxies with redshifts 5,700 km/s < cz < 39,000 km/s, distributed in several long but narrow (2.5-5 degree) segments, covering 690 square degrees. For the full, flux-limited sample, the redshift-space correlation length is approximately 8 Mpc/h. The two-dimensional correlation function ��(r_p,��) shows clear signatures of both the small-scale, ``fingers-of-God'' distortion caused by velocity dispersions in collapsed objects and the large-scale compression caused by coherent flows, though the latter cannot be measured with high precision in the present sample. The inferred real-space correlation function is well described by a power law, ��(r)=(r/6.1+/-0.2 Mpc/h)^{-1.75+/-0.03}, for 0.1 Mpc/h < r < 16 Mpc/h. The galaxy pairwise velocity dispersion is ��_{12} ~ 600+/-100 km/s for projected separations 0.15 Mpc/h < r_p < 5 Mpc/h. When we divide the sample by color, the red galaxies exhibit a stronger and steeper real-space correlation function and a higher pairwise velocity dispersion than do the blue galaxies. The relative behavior of subsamples defined by high/low profile concentration or high/low surface brightness is qualitatively similar to that of the red/blue subsamples. Our most striking result is a clear measurement of scale-independent luminosity bias at r < 10 Mpc/h: subsamples with absolute magnitude ranges centered on M_*-1.5, M_*, and M_*+1.5 have real-space correlation functions that are parallel power laws of slope ~ -1.8 with correlation lengths of approximately 7.4 Mpc/h, 6.3 Mpc/h, and 4.7 Mpc/h, respectively., 51 pages, 18 figures. Replaced to match accepted ApJ version

We analyze high-redshift structure in three hydrodynamic simulations that have identical initial conditions and cosmological parameters and differ only in the value of the baryon density parameter, Omega_b=0.02, 0.05, 0.125. Increasing Omega_b does not change the fraction of baryons in the diffuse (unshocked) phase of the intergalactic medium, but it increases cooling rates and therefore transfers some baryons from the shocked intergalactic phase to the condensed phase associated with galaxies. Predictions of Lyman-alpha forest absorption are almost unaffected by changes of Omega_b provided that the UV background intensity is adjusted so that the mean opacity of the forest matches the observed value. The required UV background intensity scales as Omega_b^1.7, and the higher photoionization rate increases the gas temperature in low density regions. Damped Lyman-alpha absorption and Lyman limit absorption both increase with increasing Omega_b, though the impact is stronger for damped absorption and is weaker at z=4 than at z=2-3. The mass of cold gas and stars in high-redshift galaxies increases faster than Omega_b but slower than Omega_b^2, and the global star formation rate scales approximately as Omega_b^1.5. In the higher Omega_b models, the fraction of baryonic material within the virial radius of dark matter halos is usually higher than the universal fraction, indicating that gas dynamics and cooling can lead to over-representation of baryons in virialized systems. On the whole, our results imply a fairly intuitive picture of the influence of Omega_b on high-redshift structure, and we provide scalings that can be used to estimate the impact of Omega_b uncertainties on the predictions of hydrodynamic simulations., Comment: 22 pages, 9 figures, submitted to ApJ, high-resolution version availible at http://lahmu.phyast.pitt.edu/~gardner/publications/omegab.ps.gz

We examine the cooling radiation from forming galaxies in hydrodynamic simulations of the LCDM model (cold dark matter with a cosmological constant), focusing on the Ly-alpha line luminosities of high-redshift systems. Primordial composition gas condenses within dark matter potential wells, forming objects with masses and sizes comparable to the luminous regions of observed galaxies. As expected, the energy radiated in this process is comparable to the gravitational binding energy of the baryons, and the total cooling luminosity of the galaxy population peaks at z ~= 2. However, in contrast to the classical picture of gas cooling from the \sim 10^6 K virial temperature of a typical dark matter halo, we find that most of the cooling radiation is emitted by gas with T < 20,000 K. As a consequence, roughly 50% of this cooling radiation emerges in the Ly-alpha line. While a galaxy's cooling luminosity is usually smaller than the ionizing continuum luminosity of its young stars, the two are comparable in the most massive systems, and the cooling radiation is produced at larger radii, where the Ly-alpha photons are less likely to be extinguished by dust. We suggest, in particular, that cooling radiation could explain the two large (\sim 100 kpc), luminous (L_{Ly-alpha} \sim 10^{44} erg s^{-1}) ``blobs'' of Ly-alpha emission found in Steidel et al.'s (1999) narrow band survey of a z = 3 proto-cluster. Our simulations predict objects of the observed luminosity at about the right space density, and radiative transfer effects can account for the observed sizes and line widths. We discuss observable tests of this hypothesis for the nature of the Ly-alpha blobs, and we present predictions for the contribution of cooling radiation to the Ly-alpha luminosity function of galaxies as a function of redshift., Submitted to ApJ. 28 pages including 9 PS figures. Version with color figures available at http://donald.astro.umass.edu/~fardal/papers/cooling/cooling.html

Measurements of the cosmological density parameter (Omega) using techniques that exploit the gravity-induced motions of galaxies yield, in linear perturbation theory, the degenerate parameter combination beta=Omega^{0.6}/b, where the linear bias parameter b is the ratio of the fluctuation amplitudes of the galaxy and mass distributions. However, the relation between the mass and the galaxy density fields depends on the complex physics of galaxy formation, and it can in general be non-linear, non-local, and stochastic. There is a growing consensus that the one-parameter model for bias is oversimplified. This leaves us with the following question: What is the quantity that is actually being measured by the different techniques? In order to address this question, we present estimates of beta from galaxy distributions constructed by applying a variety of biased galaxy formation models to cosmological N-body simulations. We compare the values of beta estimated using two different techniques: the anisotropy of the redshift-space power spectrum and an idealized version of the POTENT method. In most cases, we find that the bias factor b=Omega^{0.6}/beta derived from redshift-space anisotropy or POTENT is similar to the large-scale value of b_{sigma}(R) defined by the ratio of rms fluctuation amplitudes of the galaxy and mass distributions. However, non-linearity of bias and residual effects of non-linear gravitational evolution both influence beta estimates at the 10-20% level., 4 pages, 1 figure, Cosmic Flows Workshop, Victoria, Canada, July 1999, ed. S. Courteau, M. Strauss & J. Willick, ASP series

We determine the evolution from $z=3\to 0$ of the galaxy and mass correlation functions and bias factor in a $50h^{-1}$Mpc $\Lambda$CDM hydrodynamic simulation with $10h^{-1}$kpc resolution. The mass correlation function grows with time, but the galaxy correlation function shows little evolution and is well described by a power law. At early times, galaxies are biased traces of mass, with bias being higher on smaller scales. By z=0, galaxies trace the mass, and the bias shows little scale dependence., Comment: 2 pages, contribution to the Proceedings of Rencontres Internationales de l'IGRAP, Clustering at High Redshift, Marseille 1999

We measure the topology (genus curve) of the galaxy distribution in a mock redshift catalog designed to resemble the upcoming Sloan Digital Sky Survey (SDSS). The catalog, drawn from a large N-body simulation of a Lambda-CDM cos- mological model, mimics the anticipated spectroscopic selection procedures of the SDSS in some detail. Sky maps, redshift slices, and 3-D contour maps of the mock survey reveal a rich and complex structure, including networks of voids and superclusters that resemble the patterns seen in the CfA redshift survey and the Las Campanas Redshift Survey (LCRS). The 3-D genus curve can be measured from the simulated catalog with superb precision; this curve has the general shape predicted for Gaussian, random phase initial conditions, but the error bars are small enough to demonstrate with high significance the subtle departures from this shape caused by non-linear gravitational evolution. These distortions have the form predicted by Matsubara's (1994) perturbative anal- ysis, but they are much smaller in amplitude. We also measure the 3-D genus curve of the radial peculiar velocity field measured by applying distance- indicator relations (with realistic errors) to the mock catalog. This genus curve is consistent with the Gaussian random phase prediction, though it is of relatively low precision because of the large smoothing length required to overcome noise in the measured velocity field. Finally, we measure the 2-D topology in redshift slices, similar to early slices from the SDSS and to slices already observed in the LCRS. The genus curves of these slices are consistent with the observed genus curves of the LCRS, providing further evidence in favor of the inflationary CDM model with Omega_M~0.4. The catalog is publicly available at http://www.astronomy.ohio-state.edu/~dhw/sdss.html., ASTeX 4.0 Preprint Style, 5 GIF figures (Figs 1, 2, 3a, 3b, 6; see http://cfa-www.harvard.edu/~wcolley/SDSS_Top/ for PostScript versions), 7 PostScript figures. Figure 5 and Table 1 have minor corrections since publication

What type of objects are being detected as $z\sim 3$ "Lyman break galaxies"? Are they predominantly the most massive galaxies at that epoch, or are many of them smaller galaxies undergoing a short-lived burst of merger-induced star formation? We attempt to address this question using high-resolution cosmological hydrodynamic simulations including star formation and feedback. Our $\Lambda$CDM simulation, together with Bruzual-Charlot population synthesis models, reproduces the observed number density and luminosity function of Lyman break galaxies when dust is incorporated. The inclusion of dust is crucial for this agreement. In our simulation, these galaxies are predominantly the most massive objects at this epoch, and have a significant population of older stars. Nevertheless, it is possible that our simulations lack the resolution and requisite physics to produce starbursts, despite having a physical resolution of $\la 700$ pc at z=3. Thus we cannot rule out merger-induced starburst galaxies also contributing to the observed population of high-redshift objects., Comment: 5 pages, contribution to the Proceedings of Rencontres Internationales de l'IGRAP, Clustering at High Redshift, Marseille 1999

We estimate the value of the matter density parameter \Omega_0 by combining constraints from the galaxy cluster mass function with Croft et al.'s recent measurement of the mass power spectrum, P(k), from \lya forest data. The key assumption of the method is that cosmic structure formed by gravitational instability from Gaussian primordial fluctuations. For a specified value of \Omega_0, matching the observed cluster mass function then fixes the value of \sigma_8, the rms amplitude of mass fluctuations in 8\hmpc spheres, and it thus determines the normalization of P(k) at z=0. The value of \Omega_0 also determines the ratio of P(k) at z=0 to P(k) at z=2.5, the central redshift of the \lya forest data; the ratio is different for an open universe (\Lambda=0) or a flat universe. Because the \lya forest measurement only reaches comoving scales 2\pi/k ~ 15-20\hmpc, the derived value of \Omega_0 depends on the value of the power spectrum shape parameter \Gamma, which determines the relative contribution of larger scale modes to \sigma_8. Adopting \Gamma=0.2, a value favored by galaxy clustering data, we find \Omega_0 = 0.46^{+0.12}_{-0.10} for an open universe and \Omega_0=0.34^{+0.13}_{-0.09} for a flat universe (1\sigma errors, not including the uncertainty in cluster normalization). Cluster-normalized models with \Omega_0=1 predict too low an amplitude for P(k) at z=2.5, while models with \Omega_0=0.1 predict too high an amplitude. The more general best fit parameter combination is approximately \Omega_0 + 0.2\Lambda_0 = 0.46 + 1.3(\Gamma-0.2). Analysis of larger, existing samples of QSO spectra could greatly improve the measurement of P(k) from the \lya forest, allowing a determination of \Omega_0 by this method with a precision of ~15%, limited mainly by uncertainty in the cluster mass function., Comment: Submitted to ApJ, 6 emulateapj pages w/ 2 postscript figs

We describe cosmological simulation techniques and their application to studies of cosmic structure formation, with particular attention to recent hydrodynamic simulations of structure in the high redshift universe. Collisionless N-body simulations with Gaussian initial conditions produce a pattern of sheets, filaments, tunnels, and voids that resembles the observed large scale galaxy distribution. Simulations that incorporate gas dynamics and dissipation form dense clumps of cold gas with sizes and masses similar to the luminous parts of galaxies. Models based on inflation and cold dark matter predict a healthy population of high redshift galaxies, including systems with star formation rates of 20 M_{\sun}/year at z=6. At z~3, most of the baryons in these models reside in the low density intergalactic medium, which produces fluctuating Lyman-alpha absorption in the spectra of background quasars. The physical description of this ``Lyman-alpha forest'' is particularly simple if the absorption spectrum is viewed as a 1-dimensional map of a continuous medium instead of a collection of lines. The combination of superb observational data and robust numerical predictions makes the Lyman-alpha forest a promising tool for testing cosmological models., Comment: Latex w/ paspconf.sty, 25 pages, 8 ps figs. To appear in Origins, eds. J. M. Shull, C. E. Woodward, & H. Thronson (ASP Conference Series)