Where do "red and dead" early-type void galaxies come from?

Void regions of the Universe offer a special environment for studying cosmology and galaxy formation, which may expose weaknesses in our understanding of these phenomena. Although galaxies in voids are observed to be predominately gas rich, star forming and blue, a sub-population of bright red void galaxies can also be found, whose star formation was shut down long ago. Are the same processes that quench star formation in denser regions of the Universe also at work in voids? We compare the luminosity function of void galaxies in the 2dF Galaxy Redshift Survey, to those from a galaxy formation model built on the Millennium Simulation. We show that a global star formation suppression mechanism in the form of low luminosity "radio mode" AGN heating is sufficient to reproduce the observed population of void early-types. Radio mode heating is environment independent other than its dependence on dark matter halo mass, where, above a critical mass threshold of approximately M_vir~10^12.5 M_sun, gas cooling onto the galaxy is suppressed and star formation subsequently fades. In the Millennium Simulation, the void halo mass function is shifted with respect to denser environments, but still maintains a high mass tail above this critical threshold. In such void halos, radio mode heating remains efficient and red galaxies are found; collectively these galaxies match the observed space density without any modification to the model. Consequently, galaxies living in vastly different large-scale environments but hosted by halos of similar mass are predicted to have similar properties, consistent with observations.Comment: 6 pages, 3 figures, accepted MNRA

Cosmic Voids and Galaxy Bias in the Halo Occupation Framework

(Abridged) We investigate the power of void statistics to constrain galaxy bias and the amplitude of dark matter fluctuations. We use the halo occupation distribution (HOD) framework to describe the relation between galaxies and dark matter. After choosing HOD parameters that reproduce the mean space density n_gal and projected correlation function w_p measured for galaxy samples with M_r<-19 and M_r<-21 from the Sloan Digital Sky Survey (SDSS), we predict the void probability function (VPF) and underdensity probability function (UPF) of these samples by populating the halos of a large, high-resolution N-body simulation. If we make the conventional assumption that the HOD is independent of large scale environment at fixed halo mass, then models constrained to match n_gal and w_p predict nearly identical void statistics, independent of the scatter between halo mass and central galaxy luminosity or uncertainties in HOD parameters. Models with sigma_8=0.7 and sigma_8=0.9 also predict very similar void statistics. However, the VPF and UPF are sensitive to environmental variations of the HOD in a regime where these variations have little impact on w_p. For example, doubling the minimum host halo mass in regions with large scale (5 Mpc/h) density contrast delta<-0.65 has a readily detectable impact on void probabilities of M_r<-19 galaxies, and a similar change for delta<-0.2 alters the void probabilities of M_r<-21 galaxies at a detectable level. The VPF and UPF provide complementary information about the onset and magnitude of density- dependence in the HOD. By detecting or ruling out HOD changes in low density regions, void statistics can reduce systematic uncertainties in the cosmological constraints derived from HOD modeling, and, more importantly, reveal connections between halo formation history and galaxy properties.Comment: emulateapj, 16 pages, 13 figure

From Galaxy-Galaxy Lensing to Cosmological Parameters

Galaxy-galaxy lensing measures the mean excess surface density DS(r) around a sample of lensing galaxies. We develop a method for combining DS(r) with the galaxy correlation function xi_gg(r) to constrain Omega_m and sigma_8, going beyond the linear bias model to reach the level of accuracy demanded by current and future measurements. We adopt the halo occupation distribution (HOD) framework, and we test its applicability to this problem by examining the effects of replacing satellite galaxies in the halos of an SPH simulation with randomly selected dark matter particles from the same halos. The difference between dark matter and satellite galaxy radial profiles has a ~10% effect on DS(r) at r<1 Mpc/h. However, if radial profiles are matched, the remaining impact of individual subhalos around satellite galaxies and environmental dependence of the HOD at fixed halo mass is <5% in DS(r) for 0.1<r<15 Mpc/h. We develop an analytic approximation for DS(r) that incorporates halo exclusion and scale-dependent halo bias, and we demonstrate its accuracy with tests against a suite of populated N-body simulations. We use the analytic model to investigate the dependence of DS(r) and the galaxy-matter correlation function xi_gm(r) on Omega_m and sigma_8, once HOD parameters for a given cosmological model are pinned down by matching xi_gg(r). The linear bias prediction is accurate for r>2 Mpc/h, but it fails at the 30-50% level on smaller scales. The scaling of DS(r) ~ Omega_m^a(r) sigma_8^b(r) approaches the linear bias expectation a=b=1 at r>10 Mpc/h, but a(r) and b(r) vary from 0.8 to 1.6 at smaller r. We calculate a fiducial DS(r) and scaling indices a(r) and b(r) for two SDSS galaxy samples; galaxy-galaxy lensing measurements for these samples can be combined with our predictions to constrain Omega_m and sigma_8.Comment: 18 pages, 10 figures, accepted for publication in The Astrophysical Journa

Redshift space 21 cm power spectra from reionization

We construct a simple but self-consistent analytic ionization model for rapid exploration of 21cm power spectrum observables in redshift space. It is fully described by the average ionization fraction $x_e(z)$ and HII patch size $R(z)$ and has the flexibility to accommodate various reionization scenarios. The model associates ionization regions with dark matter halos of the number density required to recover $x_e$ and treats redshift space distortions self-consistently with the virial velocity of such halos. Based on this model, we study the line-of-sight structures in the brightness fluctuations since they are the most immune to foreground contamination. We explore the degeneracy between the HII patch size and nonlinear redshift space distortion in the one dimensional power spectrum. We also discuss the limitations experimental frequency and angular resolutions place on their distinguishability. Angular resolution dilutes even the radial signal and will be a serious limitation for resolving small bubbles before the end of reionization. Nonlinear redshift space distortions suggest that a resolution of order 1 -- 10\arcsec and a frequency resolution of 10kHz will ultimately be desirable to extract the full information in the radial field at $z\sim 10$. First generation instruments such as LOFAR and MWA can potentially measure radial HII patches of a few comoving Mpc and larger at the end of reionization and are unlikely to be affected by nonlinear redshift space distortions.Comment: 13 pages, 10 figures. Revised version. Includes minor changes. Adds appendix on accomodating a distribution of radii for the HII regions. Accepted for publication in Ap

The Abacus Cosmos: A Suite of Cosmological N-body Simulations

We present a public data release of halo catalogs from a suite of 125 cosmological $N$-body simulations from the Abacus project. The simulations span 40 $w$CDM cosmologies centered on the Planck 2015 cosmology at two mass resolutions, $4\times 10^{10}\;h^{-1}M_\odot$ and $1\times 10^{10}\;h^{-1}M_\odot$, in $1.1\;h^{-1}\mathrm{Gpc}$ and $720\;h^{-1}\mathrm{Mpc}$ boxes, respectively. The boxes are phase-matched to suppress sample variance and isolate cosmology dependence. Additional volume is available via 16 boxes of fixed cosmology and varied phase; a few boxes of single-parameter excursions from Planck 2015 are also provided. Catalogs spanning $z=1.5$ to $0.1$ are available for friends-of-friends and Rockstar halo finders and include particle subsamples. All data products are available at https://lgarrison.github.io/AbacusCosmosComment: 13 pages, 9 figures, 3 tables. Additional figures added for mass resolution convergence tests, and additional redshifts added for existing tests. Matches ApJS accepted versio

Environmental Effects on Real-Space and Redshift-Space Galaxy Clustering

Galaxy formation inside dark matter halos, as well as the halo formation itself, can be affected by large-scale environments. Evaluating the imprints of environmental effects on galaxy clustering is crucial for precise cosmological constraints with data from galaxy redshift surveys. We investigate such an environmental impact on both real-space and redshift-space galaxy clustering statistics using a semi-analytic model derived from the Millennium Simulation. We compare clustering statistics from original SAM galaxy samples and shuffled ones with environmental influence on galaxy properties eliminated. Among the luminosity-threshold samples examined, the one with the lowest threshold luminosity (~0.2L_*) is affected by environmental effects the most, which has a ~10% decrease in the real-space two-point correlation function (2PCF) after shuffling. By decomposing the 2PCF into five different components based on the source of pairs, we show that the change in the 2PCF can be explained by the age and richness dependence of halo clustering. The 2PCFs in redshift space are found to change in a similar manner after shuffling. If the environmental effects are neglected, halo occupation distribution modeling of the real-space and redshift-space clustering may have a less than 6.5% systematic uncertainty in constraining beta from the most affected SAM sample and have substantially smaller uncertainties from the other, more luminous samples. We argue that the effect could be even smaller in reality. In the Appendix, we present a method to decompose the 2PCF, which can be applied to measure the two-point auto-correlation functions of galaxy sub-samples in a volume-limited galaxy sample and their two-point cross-correlation functions in a single run utilizing only one random catalog.Comment: 13 pages, 6 figures, Accepted by AP

Redshift-Space Distortions with the Halo Occupation Distribution I: Numerical Simulations

We show how redshift-space distortions of the galaxy correlation function or power spectrum can constrain the matter density parameter Omega_m and the linear matter fluctuation amplitude sigma_8. We improve on previous treatments by adopting a fully non-linear description of galaxy clustering and bias, which allows us to break parameter degeneracies by combining large-scale and small- scale distortions. We consider different combinations of Omega_m and sigma_8 and find parameters of the galaxy halo occupation distribution (HOD) that yield nearly identical galaxy correlation functions in real space. We use these HOD parameters to populate the dark matter halos of large N-body simulations, from which we measure redshift-space distortions on small and large scales. We include a velocity bias parameter alpha_v that allows the velocity dispersions of satellite galaxies in halos to be systematically higher or lower than those of dark matter. Large-scale distortions are determined by the parameter combination beta = Omega_m^{0.6}/b_g, where b_g is the galaxy bias, in agreement with linear theory. However, linear theory does not accurately describe the distortions themselves on scales accessible to our simulations. We provide fitting formulas to estimate beta from the redshift-space correlation function or power spectrum, and we show that these formulas are significantly more accurate than those in the existing literature. On small scales, the ``finger-of-god'' distortions at projected separations ~0.1 Mpc/h depend on Omega_m*alpha_v^2 but are independent of sigma_8, while at intermediate separations they depend on sigma_8 as well. One can thus use redshift-space distortions over a wide range of scales to separately determine Omega_m, sigma_8, and alpha_v. (Abridged)Comment: 25 pages, submitted to Monthly Notice

Initial investigations into the damping characteristics of wire rope vibration isolators

Passive dampers composed of coils of multi-strand wire rope are investigated. Analytical results range from those produced by complex NASTRAN models to those of a Coulomb damping model with variable friction force. The latter agrees well with experiment. The Coulomb model is also utilized to generate hysteresis loops. Various other models related to early experimental investigations are described. Significant closed-form static solutions for physical properties of single-and multi-strand wire ropes are developed for certain specific geometries and loading conditions. NASTRAN models concentrate on model generation and mode shapes of 2-strand and 7-strand straight wire ropes with interfacial forces

Reductions in the dietary niche of southern sea otters (Enhydra lutris nereis) from the Holocene to the Anthropocene.

The sea otter (Enhydra lutris) is a marine mammal hunted to near extinction during the 1800s. Despite their well-known modern importance as a keystone species, we know little about historical sea otter ecology. Here, we characterize the ecological niche of ancient southern sea otters (E. lutris nereis) using δ13C analysis and δ15N analysis of bones recovered from archaeological sites spanning ~7,000 to 350 years before present (N = 112 individuals) at five regions along the coast of California. These data are compared with previously published data on modern animals (N = 165) and potential modern prey items. In addition, we analyze the δ15N of individual amino acids for 23 individuals to test for differences in sea otter trophic ecology through time. After correcting for tissue-specific and temporal isotopic effects, we employ nonparametric statistics and Bayesian niche models to quantify differences among ancient and modern animals. We find ancient otters occupied a larger isotopic niche than nearly all modern localities; likely reflecting broader habitat and prey use in prefur trade populations. In addition, ancient sea otters at the most southerly sites occupied an isotopic niche that was more than twice as large as ancient otters from northerly regions. This likely reflects greater invertebrate prey diversity in southern California relative to northern California. Thus, we suggest the potential dietary niche of sea otters in southern California could be larger than in central and northern California. At two sites, Año Nuevo and Monterey Bay, ancient otters had significantly higher δ15N values than modern populations. Amino acid δ15N data indicated this resulted from shifting baseline isotope values, rather than a change in sea otter trophic ecology. Our results help in better understanding the contemporary ecological role of sea otters and exemplify the strength of combing zooarchaeological and biological information to provide baseline data for conservation efforts