arXiv subjects

Andreas A. Berlind

Publications and source records attributed to Andreas A. Berlind.

At least 73 records · Page 4Linked to original sources

arXiv2008

The Intrinsic Properties of SDSS Galaxies

The observed properties of galaxies vary with inclination; for most applications we would rather have properties that are independent of inclination, intrinsic properties. One way to determine inclination corrections is to consider a large sample of galaxies, study how the observed properties of these galaxies depend on inclination and then remove this dependence to recover the intrinsic properties. We perform such an analysis for galaxies selected from the Sloan Digital Sky Survey which have been matched to galaxies from the Two-Micron All Sky Survey. We determine inclination corrections for these galaxies as a function of galaxy luminosity and Sersic index. In the g-band these corrections reach as as high as 1.2 mag and have a median value of 0.3 mag for all galaxies in our sample. We find that the corrections show little dependence on galaxy luminosity, except in the $u$ band, but are strongly dependent on galaxy Sersic index. We find that the ratio of red-to-blue galaxies changes from 1:1 to 1:2 when going from observed to intrinsic colors for galaxies in the range -22.75 < M_K < -17.75. We also discuss how survey completeness and photometric redshifts should be determined when taking into account that observed and intrinsic properties differ. Finally, we examine whether previous determinations of stellar mass give an intrinsic quantity or one that depends on galaxy inclination.

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arXiv2007

Large-Angular-Scale Clustering as a Clue to the Source of UHECRs

We show that future Ultra-High Energy Cosmic Ray samples should be able to distinguish whether the sources of UHECRs are hosted by galaxy clusters or ordinary galaxies, or whether the sources are uncorrelated with the large-scale structure of the universe. Moreover, this is true independently of arrival direction uncertainty due to magnetic deflection or measurement error. The reason for this is the simple property that the strength of large-scale clustering for extragalactic sources depends on their mass, with more massive objects, such as galaxy clusters, clustering more strongly than lower mass objects, such as ordinary galaxies.

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arXiv2007

The Physics of Galaxy Clustering I: A Model for Subhalo Populations

(Abridged) We present a semi-analytic model for Cold Dark Matter halo substructure that can be used as a framework for studying galaxy formation and an ingredient in halo models of galaxy clustering. We perform a comprehensive comparison of the model to the results of a suite of high-resolution cosmological simulations. The comparisons reveal that subhalo statistics, such as velocity and mass functions, radial distributions, and the halo occupation distributions, agree well over three orders of magnitude in host halo mass at various redshifts. Both in the simulations and in our model, the radial distributions of subhalos are significantly shallower than that of the dark matter density. The abundance of subhalos in a host is set by competition between destruction and new accretion. High mass halos and halos at high redshift tend to host more subhalos because the subhalos have, on average, been accreted more recently. Similarly, at fixed mass, halos that formed more recently host more subhalos. Observed "fossil groups" may represent an extreme tail of this correlation. We find a related correlation between host halo concentration and subhalo abundance at fixed host mass, Nsat ~ c^-a, where a changes with redshift and host-to-subhalo mass ratio. Lastly, we use our model to populate host halos in one of our high-resolution cosmological simulations, replacing the subhalos resolved in the simulation with subhalos computed according to our model. We show that the resulting 2pt correlation function of such a "hybrid" halo ensemble is indistinguishable from that measured directly in the simulation. This supports one of the key tenets of the standard halo model -- the assumption that the halo occupation distribution is statistically independent of host halo environment.

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arXiv2006

The asymmetric relations among galaxy color, structure, and environment

We investigate the dependences of galaxy star-formation history and galaxy morphology on environment, using color and H-alpha equivalent width as star-formation history indicators, using concentration and central surface brightness as morphological indicators, and using clustocentric distance as an environment indicator. Clustocentric distance has the virtue that it can be measured with very high precision over a large dynamic range. We find the following asymmetry between morphological and star-formation history parameters: star-formation history parameters relate directly to the clustocentric distance while morphological parameters relate to the clustocentric distance only indirectly through their relationships with star-formation history. This asymmetry has important implications for the role that environment plays in shaping galaxy properties and it places strong constraints on theoretical models of galaxy formation. Current semi-analytic models do not reproduce this effect.

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arXiv2006

The Clustering of Galaxy Groups: Dependence on Mass and Other Properties

We investigate the clustering of galaxy groups and clusters in the SDSS using the Berlind et al. (2006) group sample, which is designed to identify galaxy systems that each occupy a single dark matter halo. We estimate group masses from their abundances, and measure their relative large-scale bias as a function of mass. Our measurements are in agreement with the theoretical halo bias function, given a standard LCDM cosmological model, and they tend to favor a low value of the power spectrum amplitude sigma_8. We search for a residual dependence of clustering on other group properties at fixed mass, and find the strongest signal for central galaxy color in high mass groups. Massive groups with less red central galaxies are more biased on large scales than similar mass groups with redder central galaxies. We show that this effect is unlikely to be caused by errors in our mass estimates, and is most likely observational evidence of recent theoretical findings that halo bias depends on a ``second parameter'' other than mass, such as age or concentration. To compare with the data, we study the bias of massive halos in N-body simulations and quantify the strength of the relation between halo bias and concentration at fixed mass. In addition to confirming a non-trivial prediction of the LCDM cosmological model, these results have important implications for the role that environment plays in shaping galaxy properties.

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arXiv2006

What aspects of galaxy environment matter?

We determine what aspects of the density field surrounding galaxies most affect their properties. For Sloan Digital Sky Survey galaxies, we measure the group environment, meaning the host group luminosity and the distance from the group center (hereafter, ``groupocentric distance''). For comparison, we measure the surrounding density field on scales ranging from 100 kpc/h to 10 Mpc/h. We use the relationship between color and group environment to test the null hypothesis that only the group environment matters, searching for a residual dependence of properties on the surrounding density. Generally, red galaxies are slightly more clustered on small scales (about 100--300 kpc/h) than the null hypothesis predicts, possibly indicating that substructure within groups has some importance. At large scales (> 1 Mpc/h), the actual projected correlation functions of galaxies are biased at less than the 5% level with respect to the null hypothesis predictions. We exclude strongly the converse null hypothesis, that only the surrounding density (on any scale) matters. These results generally encourage the use of the halo model description of galaxy bias, which models the galaxy distribution as a function of host halo mass alone. We compare these results to proposed galaxy formation scenarios within the Cold Dark Matter cosmological model.

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arXiv2006

Percolation Galaxy Groups and Clusters in the SDSS Redshift Survey: Identification, Catalogs, and the Multiplicity Function

We identify galaxy groups and clusters in volume-limited samples of the SDSS redshift survey, using a redshift-space friends-of-friends algorithm. We optimize the friends-of-friends linking lengths to recover galaxy systems that occupy the same dark matter halos, using a set of mock catalogs created by populating halos of N-body simulations with galaxies. Extensive tests with these mock catalogs show that no combination of perpendicular and line-of-sight linking lengths is able to yield groups and clusters that simultaneously recover the true halo multiplicity function, projected size distribution, and velocity dispersion. We adopt a linking length combination that yields, for galaxy groups with ten or more members: a group multiplicity function that is unbiased with respect to the true halo multiplicity function; an unbiased median relation between the multiplicities of groups and their associated halos; a spurious group fraction of less than ~1%; a halo completeness of more than ~97%; the correct projected size distribution as a function of multiplicity; and a velocity dispersion distribution that is ~20% too low at all multiplicities. These results hold over a range of mock catalogs that use different input recipes of populating halos with galaxies. We apply our group-finding algorithm to the SDSS data and obtain three group and cluster catalogs for three volume-limited samples that cover 3495.1 square degrees on the sky. We correct for incompleteness caused by fiber collisions and survey edges, and obtain measurements of the group multiplicity function, with errors calculated from realistic mock catalogs. These multiplicity function measurements provide a key constraint on the relation between galaxy populations and dark matter halos.

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arXiv2006

What triggers galaxy transformations? The environments of post-starburst galaxies

(abridged) There are good observational reasons to believe that the progenitors of red galaxies have undergone starbursts, followed by a post-starburst phase. We investigate the environments of post-starburst galaxies by measuring \textsl{(1)} number densities in $8 h^{-1} \mathrm{Mpc}$ radius comoving spheres, \textsl{(2)} transverse distances to nearest Virgo-like galaxy clusters, and \textsl{(3)} transverse distances to nearest luminous-galaxy neighbors. We compare the post-starburst galaxies to currently star-forming galaxies identified solely by A-star excess or $\Halpha$ emission. We find that post-starburst galaxies are in the same kinds of environments as star-forming galaxies; this is our ``null hypothesis''. More importantly, we find that at each value of the A-star excess, the star-forming and post-starburst galaxies lie in very similar distributions of environment. The only deviations from our null hypothesis are barely significant: a slight deficit of post-starburst galaxies (relative to the star-forming population) in very low-density regions, a small excess inside the virial radii of clusters, and a slight excess with nearby neighbors. None of these effects is strong enough to make the post-starburst galaxies a high-density phenomenon, or to argue that the starburst events are primarily triggered by external tidal impulses (e.g., from close passages of massive galaxies). The small excess inside cluster virial radii suggests that some post-starbursts are triggered by interactions with the intracluster medium, but this represents a very small fraction of all post-starburst galaxies.

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arXiv2006

What galaxies know about their nearest cluster

We investigate the extent to which galaxies' star-formation histories and morphologies are determined by their clustocentric distance and their nearest cluster's richness. We look at three tracers of star-formation history (i-band absolute magnitude M_i, [g-r] color, and Halpha emission line equivalent width) and two indicators of galaxy morphology (surface brightness and radial concentration) for 52,569 galaxies in the redshift range of 0.015<z<0.068. We find that our morphology indicators relate to the clustocentric distance only indirectly through their relationships with stellar population and starformation rate. Galaxies that are near the cluster center tend to be more luminous, redder and have lower Halpha EW (ie, lower star-formation rates) than those that lie near or outside the virial radius of the cluster. The detailed relationships between these galaxy properties and clustocentric distance depend on cluster richness. For richer clusters, we find that (i) the transition in color and Halpha EW from cluster center to field values is more abrupt and occurs closer to the cluster virial radius, and (ii) the color and Halpha EW distributions are overall narrower than in less rich clusters. We also find that the radial gradient seen in the luminosity distribution is strongest around the smaller clusters and decreases as cluster richness increases. We find there is a `characteristic distance' at around one virial radius (the infall region) where the change with radius of galaxy property distributions is most dramatic, but we find no evidence for infall-triggered star bursts. These results suggest that galaxies `know' the distance to, and the size of, their nearest cluster and they express this information in their star-formation histories.

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arXiv2005

Very Small-Scale Clustering and Merger Rate of Luminous Red Galaxies

We present the small-scale (0.01<r<8 h^{-1} Mpc) projected correlation function w_p(r_p) and real space correlation function xi(r) of 24520 luminous early-type galaxies from the Sloan Digital Sky Survey Luminous Red Galaxy (LRG) sample (0.16<z<0.36). ``Fiber collision'' incompleteness of the SDSS spectroscopic sample at scales smaller than 55 arcseconds prevents measurements of the correlation function for LRGs on scales smaller than ~0.3 Mpc by the usual methods. In this work, we cross-correlate the spectroscopic sample with the imaging sample, with a weighting scheme to account for the collisions, extensively tested against mock catalogs. We correct for photometric biases in the SDSS imaging of close galaxy pairs. We find that the correlation function xi(r) is surprisingly close to a r^{-2} power law over more than 4 orders of magnitude in separation r. This result is too steep at small scales to be explained in current versions of the halo model for galaxy clustering. We infer an LRG-LRG merger rate of less than or similar to 0.6 Gyr^{-1} Gpc^{-3} for this sample. This result suggests that the LRG-LRG mergers are not the main mode of mass growth for LRGs at z<0.36.

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arXiv2005

On Departures From a Power Law in the Galaxy Correlation Function

We measure the projected correlation function w_p(r_p) from the Sloan Digital Sky Survey for a flux-limited sample of 118,000 galaxies and for a volume limited subset of 22,000 galaxies with absolute magnitude M_r<-21. Both correlation functions show subtle but systematic departures from the best-fit power law, in particular a change in slope at r_p~1-2 Mpc/h. These departures are stronger for the volume-limited sample, which is restricted to relatively luminous galaxies. We show that the inflection point in w_p(r_p) can be naturally explained by contemporary models of galaxy clustering, according to which it marks the transition from a large scale regime dominated by galaxy pairs in separate dark matter halos to a small scale regime dominated by galaxy pairs in the same dark matter halo. For example, given the dark halo population predicted by an inflationary cold dark matter scenario, the projected correlation function of the volume-limited sample can be well reproduced by a model in which the mean number of M_r<-21 galaxies in a halo of mass M>M_1=4.74 X 10^{13}\msun/h is _M=(M/M_1)^{0.89}, with 75% of the galaxies residing in less massive, single-galaxy halos. This physically motivated model has the same number of free parameters as a power law, and it fits the w_p(r_p) data better, with a χ^2/d.o.f.=0.93 compared to 6.12 (for 10 degrees of freedom, incorporating the covariance of the correlation function errors). Departures from a power-law correlation function encode information about the relation between galaxies and dark matter halos. Higher precision measurements of these departures for multiple classes of galaxies will constrain galaxy bias and provide new tests of the theory of galaxy formation.

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arXiv2005

Foreground and Source of a Cluster of Ultra-high Energy Cosmic Rays

We investigate the origin of a nearly pointlike cluster of 5 ultrahigh energy cosmic rays at RA ~169.2deg and dec ~56.8deg, using Sloan Digital Sky Survey and other data. No particular source candidates are found near the estimated source direction, but the direction is exceptional in having a likely merging pair of galaxy clusters at 140/h Mpc, with an unusually low foreground density. Large scale shocks or another product of the merging galaxy clusters may accelerate the UHECRs, or the merging galaxy clusters may be coincidental and the UHECRs may be accelerated in a rare event of an unexceptional progenitor. Low magnetic deflections in the foreground void may explain why this is the only identified pointlike cluster of so many UHECRs.

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arXiv2005

Theoretical Models of the Halo Occupation Distribution: Separating Central and Satellite Galaxies

The halo occupation distribution (HOD) describes the relation between galaxies and dark matter at the level of individual dark matter halos. The properties of galaxies residing at the centers of halos differ from those of satellite galaxies because of differences in their formation histories. Using a smoothed particle hydrodynamics (SPH) simulation and a semi-analytic (SA) galaxy formation model, we examine the separate contributions of central and satellite galaxies to the HOD, more specifically to the probability P(N|M) that a halo of virial mass M contains N galaxies of a particular class. In agreement with earlier results for dark matter subhalos, we find that the mean occupation function for galaxies above a baryonic mass threshold can be approximated by a step function for central galaxies plus a power law for satellites, and that the distribution of satellite numbers is close to Poisson at fixed halo mass. For galaxy samples defined by different baryonic mass thresholds, there is a nearly linear relation between the minimum halo mass Mmin required to host a central galaxy and the mass M1 at which an average halo hosts one satellite, with M1 ~ 14 Mmin (SPH) or M1 ~ 18 Mmin (SA). The mean occupation number of young galaxies exhibits a local minimum at M ~ 10 Mmin where halos are too massive to host a young central galaxy but not massive enough to host satellites. We show that the conditional galaxy mass function at fixed halo mass cannot be described by a Schechter function because central galaxies produce a "bump" at high masses. We suggest parameterizations for the HOD and the conditional luminosity function that can be used to model observed galaxy clustering. Many of our predictions are in good agreement with recent results inferred from clustering in the Sloan Digital Sky Survey.

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arXiv2005

Cosmology and the Halo Occupation Distribution from Small-Scale Galaxy Clustering in the Sloan Digital Sky Survey

We use the projected correlation function w_p(r_p) of a volume-limited subsample of the Sloan Digital Sky Survey (SDSS) main galaxy redshift catalogue to measure the halo occupation distribution (HOD) of the galaxies of the sample. Simultaneously, we allow the cosmology to vary within cosmological constraints imposed by cosmic microwave background experiments in a Lambda-CDM model. We find that combining w_p(r_p) for this sample alone with the observations by WMAP, ACBAR, CBI and VSA can provide one of the most precise techniques available to measure cosmological parameters. For a minimal flat six-parameter Lambda-CDM model with an HOD with three free parameters, we find Omega_m=0.278^{+0.027}_{-0.027}, sigma_8=0.812^{+0.028}_{-0.027}, and H_0=69.8^{+2.6}_{-2.6}km s^{-1} Mpc^{-1}; these errors are significantly smaller than from CMB alone and similar to those obtained by combining CMB with the large-scale galaxy power spectrum assuming scale-independent bias. The corresponding HOD parameters describing the minimum halo mass and the normalization and cut-off of the satellite mean occupation are M_min=(3.03^{+0.36}_{-0.36})x 10^{12} h^{-1} M_sun, M_1 = (4.58^{+0.60}_{-0.60})x 10^{13} h^{-1} M_sun, and kappa=4.44^{+0.51}_{-0.69}. When more parameters are added to the HOD model, the error bars on the HOD parameters increase because of degeneracies, but the error bars on the cosmological parameters do not increase greatly. Similar modeling for other galaxy samples could reduce the statistical errors on these results, while more thorough investigations of the cosmology dependence of nonlinear halo bias and halo mass functions are needed to eliminate remaining systematic uncertainties, which may be comparable to statistical uncertainties.

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arXiv2004

Interpreting the Relationship Between Galaxy Luminosity, Color and Environment

We study the relationship between galaxy luminosity, color, and environment in a cosmological simulation of galaxy formation. We compare the predicted relationship with that found for SDSS galaxies and find that the model successfully predicts most of the qualitative features seen in the data, but also shows some interesting differences. Specifically, the simulation predicts that the local density around bright red galaxies is a strong increasing function of luminosity, but does not depend much on color at fixed luminosity. Moreover, we show that this is due to central galaxies in dark matter halos whose baryonic masses correlate strongly with halo mass. The simulation also predicts that the local density around blue galaxies is a strong increasing function of color, but does not depend much on luminosity at fixed color. We show that this is due to satellite galaxies in halos whose stellar ages correlate with halo mass. Finally, the simulation fails to predict the luminosity dependence of environment observed around low luminosity red galaxies. However, we show that this is most likely due to the simulation's limited resolution. A study of a higher resolution, smaller volume simulation suggests that this dependence is caused by the fact that all low luminosity red galaxies are satellites in massive halos, whereas intermediate luminosity red galaxies are a mixture of satellites in massive halos and central galaxies in less massive halos.

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arXiv2004

The Dark Side of the Halo Occupation Distribution

We analyze the halo occupation distribution (HOD), the probability for a halo of mass M to host a number of subhalos N, and two-point correlation function of galaxy-size dark matter halos using high-resolution dissipationless simulations of the concordance flat LCDM model. The halo samples include both the host halos and the subhalos, distinct gravitationally-bound halos within the virialized regions of larger host systems. We find that the first moment of the HOD, (M), has a complicated shape consisting of a step, a shoulder, and a power law high-mass tail. The HOD can be described by a Poisson statistics at high halo masses but becomes sub-Poisson for <4. We show that the HOD can be understood as a combination of the probability for a halo of mass M to host a central galaxy and the probability to host a given number Ns of satellite galaxies. The former can be approximated by a step-like function, while the latter can be well approximated by a Poisson distribution, fully specified by its first moment (M). We find that ~M^b with b~1 for a wide range of number densities, redshifts, and different power spectrum normalizations. This formulation provides a simple but accurate model for the halo occupation distribution found in simulations. At z=0, the two-point correlation function (CF) of galactic halos can be well fit by a power law down to ~100/h kpc with an amplitude and slope similar to those of observed galaxies. At redshifts z>~1, we find significant departures from the power-law shape of the CF at small scales. If the deviations are as strong as indicated by our results, the assumption of the single power law often used in observational analyses of high-redshift clustering is likely to bias the estimates of the correlation length and slope of the correlation function.

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arXiv2003

The Halo Occupation Distribution and the Physics of Galaxy Formation

The halo occupation distribution (HOD) describes the bias between galaxies and dark matter by specifying (a) the probability P(N|M) that a halo of virial mass M contains N galaxies of a particular class and (b) the relative distributions of galaxies and dark matter within halos. We calculate predicted HODs for a Lambda-CDM cosmological model using an SPH hydrodynamic simulation and a semi-analytic (SA) galaxy formation model. Although the two methods predict different galaxy mass functions, their HOD predictions agree remarkably well. For mass-selected samples, the mean occupation exhibits a sharp cutoff at low halo masses, a slowly rising plateau for ~1-2, and a more steeply rising high occupancy regime. At low , the mean pair and triple counts are well below Poisson expectations, with important consequences for small scale behavior of 2- and 3-point correlation functions. The HOD depends strongly on galaxy age, with high mass halos populated mainly by old galaxies and low mass halos by young galaxies. The SPH simulation supports several simplifying assumptions about HOD bias: the most massive galaxy in a halo usually lies close to the center and moves near the halo's mean velocity; satellite galaxies have the same radial profile and velocity dispersion as the dark matter; and the mean occupation at fixed halo mass is independent of the halo's larger scale environment. By applying the SPH and SA HODs to a large volume N-body simulation, we show that both methods predict slight, observable departures from a power-law galaxy correlation function. The predicted HODs are closely tied to the underlying galaxy formation physics, they offer useful guidance to theoretical models of galaxy clustering, and they will be tested empirically by ongoing analyses of galaxy redshift surveys. (Shortened)

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arXiv2002

Near-IR and Optical Morphology of Spiral Galaxies

We announce the initial release of data from the Ohio State University Bright Spiral Galaxy Survey, a BVRJHK imaging survey of a well-defined sample of 205 bright, nearby spiral galaxies. We present H-band morphological classification on the Hubble sequence for the OSU Survey sample. We compare the H-band classification to B-band classification from our own images and from standard galaxy catalogs. Our B-band classifications match well with those of the standard catalogs. On average, galaxies with optical classifications from Sa through Scd appear about one T-type earlier in the H-band than in the B-band, but with large scatter. This result does not support recent claims made in the literature that the optical and near-IR morphologies of spiral galaxies are uncorrelated. We present detailed descriptions of the H-band morphologies of our entire sample, as well as B- and H-band images for a set of 17 galaxies chosen as type examples, and BRH color-composite images of six galaxies chosen to demonstrate the range in morphological variation as a function of wavelength. Data from the survey are accessible at http://www.astronomy.ohio-state.edu/~survey/

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