arXiv subjects

Michael R. Blanton

Publications and source records attributed to Michael R. Blanton.

At least 109 records · Page 6Linked to original sources

arXiv2009

LSST Science Book, Version 2.0

A survey that can cover the sky in optical bands over wide fields to faint magnitudes with a fast cadence will enable many of the exciting science opportunities of the next decade. The Large Synoptic Survey Telescope (LSST) will have an effective aperture of 6.7 meters and an imaging camera with field of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over 20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a total point-source depth of r~27.5. The LSST Science Book describes the basic parameters of the LSST hardware, software, and observing plans. The book discusses educational and outreach opportunities, then goes on to describe a broad range of science that LSST will revolutionize: mapping the inner and outer Solar System, stellar populations in the Milky Way and nearby galaxies, the structure of the Milky Way disk and halo and other objects in the Local Volume, transient and variable objects both at low and high redshift, and the properties of normal and active galaxies at low and high redshift. It then turns to far-field cosmological topics, exploring properties of supernovae to z~1, strong and weak lensing, the large-scale distribution of galaxies and baryon oscillations, and how these different probes may be combined to constrain cosmological models and the physics of dark energy.

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arXiv2009

Physical properties and environments of nearby galaxies

We review the physical properties of nearby, relatively luminous galaxies, using results from newly available massive data sets together with more detailed observations. First, we present the global distribution of properties, including the optical and ultraviolet luminosity, stellar mass, and atomic gas mass functions. Second, we describe the shift of the galaxy population from "late" galaxy types in underdense regions to "early" galaxy types in overdense regions. We emphasize that the scaling relations followed by each galaxy type change very little with environment, with the exception of some minor but detectable effects. The shift in the population is apparent even at the densities of small groups and therefore cannot be exclusively due to physical processes operating in rich clusters. Third, we divide galaxies into four crude types -- spiral, lenticular, elliptical, and merging systems -- and describe some of their more detailed properties. We attempt to put these detailed properties into the global context provided by large surveys.

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arXiv2009

The Baryonic Acoustic Feature and Large-Scale Clustering in the SDSS LRG Sample

We examine the correlation function ξof 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 1.5σlevel. 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 (1σuncertainties 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.

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arXiv2009

Astronomical Software Wants To Be Free: A Manifesto

Astronomical software is now a fact of daily life for all hands-on members of our community. Purpose-built software for data reduction and modeling tasks becomes ever more critical as we handle larger amounts of data and simulations. However, the writing of astronomical software is unglamorous, the rewards are not always clear, and there are structural disincentives to releasing software publicly and to embedding it in the scientific literature, which can lead to significant duplication of effort and an incomplete scientific record. We identify some of these structural disincentives and suggest a variety of approaches to address them, with the goals of raising the quality of astronomical software, improving the lot of scientist-authors, and providing benefits to the entire community, analogous to the benefits provided by open access to large survey and simulation datasets. Our aim is to open a conversation on how to move forward. We advocate that: (1) the astronomical community consider software as an integral and fundable part of facility construction and science programs; (2) that software release be considered as integral to the open and reproducible scientific process as are publication and data release; (3) that we adopt technologies and repositories for releasing and collaboration on software that have worked for open-source software; (4) that we seek structural incentives to make the release of software and related publications easier for scientist-authors; (5) that we consider new ways of funding the development of grass-roots software; (6) and that we rethink our values to acknowledge that astronomical software development is not just a technical endeavor, but a fundamental part of our scientific practice.

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arXiv2008

Cross-correlation Weak Lensing of SDSS Galaxy Clusters III: Mass-to-light Ratios

We present measurements of the excess mass-to-light ratio measured aroundMaxBCG galaxy clusters observed in the SDSS. This red sequence cluster sample includes objects from small groups with masses ranging from ~5x10^{12} to ~10^{15} M_{sun}/h. Using cross-correlation weak lensing, we measure the excess mass density profile above the universal mean Δρ(r) = ρ(r) - \barρ for clusters in bins of richness and optical luminosity. We also measure the excess luminosity density Δl(r) = l(r) - \bar{l} measured in the z=0.25 i-band. For both mass and light, we de-project the profiles to produce 3D mass and light profiles over scales from 25 kpc/ to 22 Mpc/h. From these profiles we calculate the cumulative excess mass M(r) and excess light L(r) as a function of separation from the BCG. On small scales, where ρ(r) >> \barρ, the integrated mass-to-light profile may be interpreted as the cluster mass-to-light ratio. We find the M/L_{200}, the mass-to-light ratio within r_{200}, scales with cluster mass as a power law with index 0.33+/-0.02. On large scales, where ρ(r) ~ \barρ, the M/L approaches an asymptotic value independent of cluster richness. For small groups, the mean M/L_{200} is much smaller than the asymptotic value, while for large clusters it is consistent with the asymptotic value. This asymptotic value should be proportional to the mean mass-to-light ratio of the universe . We find /b^2_{ml} = 362+/-54 h (statistical). There is additional uncertainty in the overall calibration at the ~10% level. The parameter b_{ml} is primarily a function of the bias of the L <~ L_* galaxies used as light tracers, and should be of order unity. Multiplying by the luminosity density in the same bandpass we find Ω_m/b^2_{ml} = 0.02+/-0.03, independent of the Hubble parameter.

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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

The growth of luminous red galaxies by merging

We study the role of major and minor mergers in the mass growth of luminous red galaxies. We present small-scale ($0.01<r<8\,\hMpc$) projected cross-correlation functions of $23043$ luminous early-type galaxies from the Sloan Digital Sky Survey (SDSS) Luminous Red Galaxy (LRG) sample ($0.16<z<0.30$, $\MMi\approx -22.75\,\mag$) with all their companions in the SDSS imaging sample, split into color and luminosity subsamples with $\MMi<-18\,\mag$. We de-project the two-dimensional functions to obtain three-dimensional real-space LRG--galaxy cross-correlation functions for each companion subsample. We find that the cross-correlation functions are not purely power-law and that there is a clear ``one-halo'' to ``two-halo'' transition near $1\,\hMpc$. We convert these results into close pair statistics and estimate the LRG accretion rate from each companion galaxy subsample using timescales from dynamical friction arguments for each subsample of the companions. We find that the accretion onto LRGs is dominated by dry mergers of galaxies more luminous than $\Lstar$. We integrate the luminosity accretion rate from mergers over all companion galaxy subsamples and find that LRGs are growing by $[1.7\pm 0.1]$ percent per $\Gyr$, on average, from merger activity at redshift $z\sim 0.25$. This rate is almost certainly an over-estimate because we have assumed that all close pairs are merging as quickly as dynamical friction allows; nonetheless it is on the low side of the panoply of measurements in the literature, and lower than any rate predicted from theory.

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arXiv2007

Testing cold dark matter with the low mass Tully-Fisher relation

The galaxy circular velocity function at small masses is related to the matter power spectrum on small scales. Although this function is well-studied for Local Group dwarfs, theoretical predictions and observational measurements are difficult for satellite galaxies, because of ram pressure and tidal stripping. By contrast, isolated dwarf galaxies are less affected by these processes, and almost always have enough 21cm emission to trace their dynamics robustly. Here, we test cold dark matter cosmology using isolated low mass dwarf galaxies from the SDSS with measured 21cm widths. We find consistency between the predicted and observed number density of isolated galaxies down to circular velocities of 50 km/s. Our technique yields a direct test of small-scale cosmology independent of the Lyman-alpha forest power spectrum, but our sample is currently statistically less powerful: warm dark matter particles heavier than 0.5 keV cannot be ruled out. Our major systematic uncertainty is the surface brightness limit of the SDSS. Blind HI surveys, such as the ALFALFA survey on Arecibo, will uncover a larger number of isolated low mass galaxies and increase the power of our constraints. With our sample, we also find that the Tully-Fisher relation for dwarf galaxies is a strong function of environment, and that the baryonic fraction is only a weak function of mass. These results suggest that for dwarf galaxies, gas loss is dominated by external, not internal, processes. [abridged]

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arXiv2007

The Sloan Digital Sky Survey Quasar Catalog IV. Fifth Data Release

We present the fourth edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog contains 77,429 objects; this is an increase of over 30,000 entries since the previous edition. The catalog consists of the objects in the SDSS Fifth Data Release that have luminosities larger than M_i = -22.0 (in a cosmology with H_0 = 70 km/s/Mpc, Omega_M = 0.3, and Omega_Lambda = 0.7) have at least one emission line with FWHM larger than 1000 km/s, or have interesting/complex absorption features, are fainter than i=15.0, and have highly reliable redshifts. The area covered by the catalog is 5740 sq. deg. The quasar redshifts range from 0.08 to 5.41, with a median value of 1.48; the catalog includes 891 quasars at redshifts greater than four, of which 36 are at redshifts greater than five. Approximately half of the catalog quasars have i < 19; nearly all have i < 21. For each object the catalog presents positions accurate to better than 0.2 arcsec. rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains basic radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800--9200A at a spectral resolution of ~2000. The spectra can be retrieved from the public database using the information provided in the catalog. The average SDSS colors of quasars as a function of redshift, derived from the catalog entries, are presented in tabular form. Approximately 96% of the objects in the catalog were discovered by the SDSS.

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arXiv2007

Environmental Dependence of Properties of Galaxies in the Sloan Digital Sky Survey

We investigate the dependence of physical properties of galaxies brighter than M_r=-18.0 in the SDSS on environment, as measured by local density using an adaptive smoothing kernel. We find that variations of galaxy properties with environment are almost entirely due to the dependence of morphology and luminosity on environment. Because galaxy properties depend not only on luminosity but also on morphology, it is clear that galaxy properties cannot be determined solely by dark halo mass. When morphology and luminosity are fixed, other physical properties, such as color, color-gradient, concentration, size, velocity dispersion, and star formation rate, are nearly independent of local density. The only feature is the sharp decrease of late type fraction above the critical luminosity of about M_r=-21.3 in the morphology versus luminosity relation. Weak residual dependences on environment include that of the color of late-types (bluer at lower density) and of the L-sigma relation of early-types (larger dispersion at higher density for bright galaxies). The early-type fraction is a monotonically increasing function of local density and luminosity. The morphology-density- luminosity relation should be a key constraint on galaxy formation models. We demonstrate that the dependence on environment of the morphology of galaxie originates from variations in density on effective Gaussian smoothing scales much smaller than 12 h^{-1}Mpc. We find that galaxy morphology varies both with density measured on an effective Gaussian smoothing scale of 4.7 h^{-1} Mpc and on distance to the nearest bright galaxy (particularly, for about 0.2 h^{-1}Mpc). We propose a mechanism that the morphology of galaxies in galaxy systems is transformed by the tidal force.

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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

K-corrections and filter transformations in the ultraviolet, optical, and near infrared

Template fits to observed galaxy fluxes allow calculation of K-corrections and conversions among observations of galaxies at various wavelengths. We present a method for creating model-based template sets given a set of heterogeneous photometric and spectroscopic galaxy data. Our technique, non-negative matrix factorization, is akin to principle component analysis (PCA), except that it is constrained to produce nonnegative templates, it can use a basis set of models (rather than the delta function basis of PCA), and it naturally handles uncertainties, missing data, and heterogeneous data (including broad-band fluxes at various redshifts). The particular implementation we present here is suitable for ultraviolet, optical, and near-infrared observations in the redshift range 0 < z < 1.5. Since we base our templates on stellar population synthesis models, the results are intepretable in terms of approximate stellar masses and star-formation histories. We present templates fit with this method to data from GALEX, Sloan Digital Sky Survey spectroscopy and photometry, the Two-Micron All Sky Survey, the Deep Extragalactic Evolutionary Probe and the Great Observatories Origins Deep Survey. In addition, we present software for using such data to estimate K-corrections and stellar masses.

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arXiv2006

Constraining the Projected Radial Distribution of Galactic Satellites with the Sloan Digital Sky Survey

We use the Sloan Digital Sky Survey (SDSS) spectroscopic sample to constrain the projected radial distribution of satellites around isolated ~ L* galaxies. We employ mock galaxy catalogs derived from high-resolution cosmological simulations to investigate the effects of interloper contamination and show that interlopers significantly bias the estimated slope of the projected radial distribution of satellites. We also show that the distribution of interlopers around galaxies is expected to be non-uniform in velocity space because galaxies are clustered and reside in crowded environments. Successful methods of interloper contamination correction should therefore take into account environments of the host galaxies. Two such new methods are presented and the most reliable of them is used to correct for interloper contamination in analyses of the SDSS galaxy sample. The best fit power-law slope of the interloper-corrected surface density distribution of satellites, Sigma(R) ~ R^alpha, in the volume-limited SDSS sample is alpha ~ -1.7 +/- 0.1, independent of the galaxy and satellite luminosities. Comparison with Lambda-CDM simulations shows that the radial distribution of the SDSS satellites is more concentrated than that of subhalos around galaxy-sized halos, especially at R < 100 kpc/h. The predicted dark matter radial distribution is somewhat more concentrated than the profile of the SDSS satellites, but the difference is not statistically significant for our sample.

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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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arXiv2006

SDSS Pre-Burst Observations of Recent Gamma-Ray Burst Fields

In this paper, we present Sloan Digital Sky Survey (SDSS) photometry and spectroscopy in the fields of 24 gamma-ray bursts (GRBs) observed by Swift, including bursts localized by Swift, HETE-2, and INTEGRAL, after December 2004. After this bulk release, we plan to provide individual releases of similar data shortly after the localization of future bursts falling in the SDSS survey area. These data provide a solid basis for the astrometric and photometric calibration of follow-up afterglow searches and monitoring. Furthermore, the images provided with this release will allow observers to find transient objects up to a magnitude fainter than possible with Digitized Sky Survey image comparisons.

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