Cameron K. McBride

THE CLUSTERING OF MASSIVE GALAXIES AT z ∼ 0.5 FROM THE FIRST SEMESTER OF BOSS DATA

We calculate the real- and redshift-space clustering of massive galaxies at z ∼ 0.5 using the first semester of data by the Baryon Oscillation Spectroscopic Survey (BOSS). We study the correlation functions of a sample of 44,000 massive galaxies in the redshift range 0.4 <z< 0.7. We present a halo-occupation distribution modeling of the clustering results and discuss the implications for the manner in which massive galaxies at z ∼ 0.5 occupy dark matter halos. The majority of our galaxies are central galaxies living in halos of mass 10 13 h −1 M� ,b ut 10% are satellites living in halos 10 times more massive. These results are broadly in agreement with earlier investigations of massive galaxies at z ∼ 0.5. The inferred large-scale bias (b � 2) and relatively high number density ( ¯ n = 3 × 10 −4 h 3 Mpc −3 ) imply that BOSS galaxies are excellent tracers of large-scale structure, suggesting BOSS will enable a wide range of investigations on the distance scale, the growth of large-scale structure, massive galaxy evolution, and other topics.

The baryonic acoustic feature and large-scale clustering in the Sloan Digital Sky Survey luminous red galaxy sample

We examine the correlation function \xi of the Sloan Digital Sky Survey (SDSS) Luminous Red Galaxy sample (LRG) at large scales (60<s<400 Mpc/h) using the final data release (DR7; 105,831 LRGs between 0.16<z<0.47). Using mock catalogs, we demonstrate that the observed baryonic acoustic peak and larger scale signal are consistent with LCDM at the 1.5\sigma level. The signal at 155<s<200 Mpc/h tends to be high relative to theoretical expectations; this slight deviation can be attributed to a bright subsample of the LRGs. Fitting data to a non-linear, redshift-space, template based-model, we constrain the peak position at s_p=103.6+3.6-2.4 Mpc/h when fitting the range 60<s<150 Mpc/h (1\sigma uncertainties measured from the mocks. This redshift-space distance s_p is related to the comoving sound horizon scale r_s after taking into account matter clustering non-linearities, redshift distortions and galaxy clustering bias. Mock catalogs show that the probability that a DR7-sized sample would not have an identifiable peak is at least 10%. As a consistency check of a fiducial cosmology, we use the observed s_p to obtain the distance D_V=[(1+z)^2D_A^2cz/H(z)]^(1/3) relative to the acoustic scale. We find r_s/D_V(z=0.278)=0.1394+-0.0049. This result is in excellent agreement with Percival et. al (2009), who examine roughly the same data set, but using the power spectrum. Comparison with other determinations in the literature are also in very good agreement. We have tested our results against a battery of possible systematic effects, finding all effects are smaller than our estimated sample variance.We examine the correlation function ? of the Sloan Digital Sky Survey Luminous Red Galaxy sample at large scales (60 h ?1 Mpc < s < 400?h ?1?Mpc) using the final data release (DR7). Focusing on a quasi-volume-limited (0.16 < z < 0.36) subsample and utilizing mock galaxy catalogs, we demonstrate that the observed baryonic acoustic peak and larger scale signal are consistent with ?CDM at 70%-95% confidence. Fitting data to a non-linear, redshift-space, template-based model, we constrain the peak position at s p = 101.7? 3.0?h ?1?Mpc when fitting the range 60 h ?1 Mpc < s < 150?h ?1?Mpc (1? uncertainties). This redshift-space distance s p is related to the comoving sound horizon scale rs after taking into account matter-clustering non-linearities, redshift distortions, and galaxy-clustering bias. Mock catalogs show that the probability that a DR7-sized sample would not have an identifiable peak is at least ~10%. As a consistency check of a fiducial cosmology, we use the observed s p to obtain the distance relative to the acoustic scale. We find rs /DV (z = 0.278) = 0.1389?? 0.0043. This result is in excellent agreement with Percival et al., who examine roughly the same data set, but use the power spectrum. Comparison with other determinations in the literature are also in very good agreement. The signal of the full sample at 125 h ?1 Mpc < s < 200?h ?1?Mpc tends to be high relative to theoretical expectations; this slight deviation can probably be attributed to sample variance. We have tested our results against a battery of possible systematic effects, finding all effects are smaller than our estimated sample variance.

Haloes gone MAD: The Halo-Finder Comparison Project

We present a detailed comparison of fundamental dark matter halo properties retrieved by a substantial number of different halo finders. These codes span a wide range of techniques including friends-of-friends, spherical-overdensity and phase-space-based algorithms. We

THE FORMATION AND EVOLUTION OF INTRACLUSTER LIGHT

Using N-body simulations, we have modeled the production and evolution of diffuse, low surface brightness intracluster light (ICL) in three simulated galaxy clusters. Using an observational definition of ICL to be luminosity at a surface brightness µV> 26.5 mag/arcsec 2 , we have found that the fraction of cluster luminosity contained in ICL generally increases as clusters evolve, although there are large deviations from this trend over short timescales, including sustained periods of decreasing ICL luminosity. Most ICL luminosity increases come in short, discrete events which are highly correlated with group accretion events within the cluster. In evolved clusters we find that 10 - 15% of the clusters’ luminosity is at ICL surface brightness. The morphological structure of the ICL changes with time, evolving from a complex of filaments and smallscale, relatively high surface brightness features early in a cluster’s history, to a more diffuse and amorphous cluster-scale ICL envelope at later times. Finally, we also see a correlation between the evolution of ICL at different surface brightnesses, including a time delay between the evolution of faint and extremely faint surface brightness features which is traced to the differing dynamical timescales in the group and cluster environment. Subject headings: galaxies: clusters: general — galaxies: evolution — galaxies : interactions — galaxies: kinematics and dynamics — methods: N-body simulations

The clustering of galaxies at z ≈ 0.5 in the SDSS-III data release 9 BOSS-CMASS sample: a test for the ΛCDM cosmology

We present results on the clustering of 282 068 galaxies in the Baryon Oscillation Spectroscopic Survey (BOSS) sample of massive galaxies with redshifts 0.4 < z < 0.7 which is part of the Sloan Digital Sky Survey III project. Our results cover a large range of scales from ∼500 to ∼90 h−1 Mpc. We compare these estimates with the expectations of the flat Λ cold dark matter (ΛCDM) standard cosmological model with parameters compatible with Wilkinson Microwave Anisotropy Probe 7 data. We use the MultiDark cosmological simulation, one of the largest N-body runs presently available, together with a simple halo abundance matching technique, to estimate galaxy correlation functions, power spectra, abundance of subhaloes and galaxy biases. We find that the ΛCDM model gives a reasonable description to the observed correlation functions at z ≈ 0.5, which is remarkably good agreement considering that the model, once matched to the observed abundance of BOSS galaxies, does not have any free parameters. However, we find a ≳10 per cent deviation in the correlation functions for scales ≲ 1 and ∼10–40 h−1 Mpc. A more realistic abundance matching model and better statistics from upcoming observations are needed to clarify the situation. We also estimate that about 12 per cent of the ‘galaxies’ in the abundance-matched sample are satellites inhabiting central haloes with mass M ≳ 1014 h−1 M⊙. Using the MultiDark simulation, we also study the real-space halo bias b of the matched catalogue finding that b = 2.00 ± 0.07 at large scales, consistent with the one obtained using the measured BOSS-projected correlation function. Furthermore, the linear large-scale bias, defined using the extrapolated linear matter power spectrum, depends on the number density n of the abundance-matched sample as b = −0.048 − (0.594 ± 0.02)log10(n/ h3 Mpc−3). Extrapolating these results to baryon acoustic oscillation scales, we measure a scale-dependent damping of the acoustic signal produced by non-linear evolution that leads to ∼2–4 per cent dips at ≳ 3σ level for wavenumbers k ≳ 0.1 h Mpc−1 in the linear large-scale bias.

The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: the low redshift sample

We report on the small scale (0:5 < r < 40h 1 Mpc) clustering of 78895 massive (M 10 11:3 M ) galaxies at 0:2 < z < 0:4 from the first two years of data from the Baryon Oscillation Spectroscopic Survey (BOSS), to be released as part of SDSS Data Release 9 (DR9). We describe the sample selection, basic properties of the galaxies, and caveats for working with the data. We calculate the real- and redshift-space two-point correlation functions of these galaxies, fit these measurements using Halo Occupation Distribution (HOD) modeling within dark matter cosmological simulations, and estimate the errors using mock catalogs. These galaxies lie in massive halos, with a mean halo mass of 5:2 10 13 h 1 M , a large scale bias of 2:0, and a satellite fraction of 12 2%. Thus,

Three-point Correlation Functions of SDSS Galaxies: Luminosity and Color Dependence in Redshift and Projected Space

The three-point correlation function (3PCF) provides an important view into the clustering of galaxies that is not available to its lower order cousin, the two-point correlation function (2PCF). Higher order statistics, such as the 3PCF, are necessary to probe the non-Gaussian structure and shape information expected in these distributions. We measure the clustering of spectroscopic galaxies in the Main Galaxy Sample of the Sloan Digital Sky Survey, focusing on the shape or configuration dependence of the reduced 3PCF in both redshift and projected space. This work constitutes the largest number of galaxies ever used to investigate the reduced 3PCF, using over 220,000 galaxies in three volume-limited samples. We find significant configuration dependence of the reduced 3PCF at 3-27 h –1 Mpc, in agreement with ΛCDM predictions and in disagreement with the hierarchical ansatz. Below 6 h –1 Mpc, the redshift space reduced 3PCF shows a smaller amplitude and weak configuration dependence in comparison with projected measurements suggesting that redshift distortions, and not galaxy bias, can make the reduced 3PCF appear consistent with the hierarchical ansatz. The reduced 3PCF shows a weaker dependence on luminosity than the 2PCF, with no significant dependence on scales above 9 h –1 Mpc. On scales less than 9 h –1 Mpc, the reduced 3PCF appears more affected by galaxy color than luminosity. We demonstrate the extreme sensitivity of the 3PCF to systematic effects such as sky completeness and binning scheme, along with the difficulty of resolving the errors. Some comparable analyses make assumptions that do not consistently account for these effects.

The clustering of galaxies in the SDSS-III BaryonOscillation Spectroscopic Survey: measuring structuregrowth using passive galaxies

We explore the benefits of using a passively evolving population of galaxies to measure the evolution of the rate of structure growth between z = 0.25 and 0.65 by combining data from the Sloan Digital Sky Survey (SDSS) I/II and SDSS-III surveys. The large-scale linear bias of a population of dynamically passive galaxies, which we select from both surveys, is easily modelled. Knowing the bias evolution breaks degeneracies inherent to other methodologies, and decreases the uncertainty in measurements of the rate of structure growth and the normalization of the galaxy power spectrum by up to a factor of 2. If we translate our measurements into a constraint on σ8(z = 0) assuming a concordance cosmological model and general relativity (GR), we find that using a bias model improves our uncertainty by a factor of nearly 1.5. Our results are consistent with a flat Λ cold dark matter model and with GR.

THREE-POINT CORRELATION FUNCTIONS OF SDSS GALAXIES: CONSTRAINING GALAXY-MASS BIAS

We constrain the linear and quadratic bias parameters from the configuration dependence of the three-point correlation function (3PCF) in both redshift and projected space, utilizing measurements of spectroscopic galaxies in the Sloan Digital Sky Survey Main Galaxy Sample. We show that bright galaxies (Mr < –21.5) are biased tracers of mass, measured at a significance of 4.5σ in redshift space and 2.5σ in projected space by using a thorough error analysis in the quasi-linear regime (9-27 h –1 Mpc). Measurements on a fainter galaxy sample are consistent with an unbiased model. We demonstrate that a linear bias model appears sufficient to explain the galaxy-mass bias of our samples, although a model using both linear and quadratic terms results in a better fit. In contrast, the bias values obtained from the linear model appear in better agreement with the data by inspection of the relative bias and yield implied values of σ8 that are more consistent with current constraints. We investigate the covariance of the 3PCF, which itself is a measurement of galaxy clustering. We assess the accuracy of our error estimates by comparing results from mock galaxy catalogs to jackknife re-sampling methods. We identify significant differences in the structure of the covariance. However, the impact of these discrepancies appears to be mitigated by an eigenmode analysis that can account for the noisy, unresolved modes. Our joint analysis of both redshift space and projected measurements allows us to identify systematic effects affecting constraints from the 3PCF.

REGARDING THE LINE-OF-SIGHT BARYONIC ACOUSTIC FEATURE IN THE SLOAN DIGITAL SKY SURVEY AND BARYON OSCILLATION SPECTROSCOPIC SURVEY LUMINOUS RED GALAXY SAMPLES

We analyze the line-of-sight baryonic acoustic feature in the two-point correlation function ξ of the Sloan Digital Sky Survey (SDSS) luminous red galaxy (LRG) sample (0.16 < z < 0.47). By defining a narrow line-of-sight region, rp < 5.5 h −1 Mpc, where rp is the transverse separation component, we measure a strong excess of clustering at ∼ 110 h −1 Mpc, as previously reported in the literature. We also test these results in an alternative coordinate system, by defining the line-of-sight as θ < 3 ◦ , where θ is the opening angle. This clustering excess appears much stronger than the feature in the better-measured monopole. A fiducialCDM non-linear model in redshift-space predicts a much weaker signature. We use realistic mock catalogs to model the expected signal and noise. We find that the line-of-sight measurements can be explained well by our mocks as well as by a featureless ξ = 0. We conclude that there is no convincing evidence that the strong clustering measurement is the line-of-sight baryonic acoustic feature. We also evaluate how detectable such a signal would be in the upcoming Baryon Oscillation Spectroscopic Survey LRG volume (BOSS). Mock LRG catalogs (z < 0.6) suggest that: (i ) the narrow line- of-sight cylinder and cone defined above probably will not reveal a detectable acoustic feature in BOSS; (ii ) a clustering measurement as high as that in the current sample can be ruled out (or confirmed) at a high confidence level using a BOSS-sized data set; and (iii ) an analysis with wider angular cuts, which provide better signal-to-noise ratios, can nevertheless be used to compare line-of-sight and transverse distances, and thereby constrain the expansion rate H(z) and diameter distance DA(z). Subject headings: cosmology: observation - distance scale - galaxies: elliptical and lenticular, cD - large scale structure of universe