Jonathan Brinkmann

Lawrence Berkeley National Laboratory, Berkeley, California, United States

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Publications (30)146.39 Total impact

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    ABSTRACT: Photometric large scale structure (LSS) surveys probe the largest volumes in the Universe, but are inevitably limited by systematic uncertainties. Imperfect photometric calibration leads to biases in our measurements of the density fields of LSS tracers such as galaxies and quasars, and as a result in cosmological parameter estimation. Earlier studies have proposed using cross-correlations between different redshift slices or cross-correlations between different surveys to reduce the effects of such systematics. In this paper we develop a method to characterize unknown systematics. We demonstrate that while we do not have sufficient information to correct for unknown systematics in the data, we can obtain an estimate of their magnitude. We define a parameter to estimate contamination from unknown systematics using cross-correlations between different redshift slices and propose discarding bins in the angular power spectrum that lie outside a certain contamination tolerance level. We show that this method improves estimates of the bias using simulated data and further apply it to photometric luminous red galaxies in the Sloan Digital Sky Survey as a case study.
    09/2013;
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    ABSTRACT: We searched quasar spectra from the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) for the rare occurrences where a strong damped Lyman-alpha absorber (DLA) blocks the Broad Line Region emission from the quasar and acts as a natural coronagraph to reveal narrow Ly\alpha\ emission from the host galaxy. We define a statistical sample of 31 DLAs in Data Release 9 (DR9) with log N(HI) > 21.3 cm^-2 located at less than 1500 km s^-1 from the quasar redshift. In 25% (8) of these DLAs, a strong narrow Ly\alpha\ emission line is observed with flux ~25 x 10^-17 erg s^-1 cm^-2 on average. For DLAs without this feature in their troughs, the average 3-\sigma\ upper limit is < 0.8 x 10^-17 erg s^-1 cm^-2. Our statistical sample is nearly 2.5 times larger than the anticipated number of intervening DLAs in DR9 within 1500 km s^-1 of the quasar redshift. We also define a sample of 26 DLAs from DR9 and DR10 with narrow Ly\alpha\ emission detected and no limit on the HI column density to better characterize properties of the host galaxy emission. Analyzing the statistical sample, we do not find substantial differences in the kinematics, metals, or reddening for the two populations with and without emission detected. The highly symmetric narrow Ly\alpha\ emission line profile centered in the HI trough indicates that the emitting region is separate from the absorber. The luminosity of the narrow Ly\alpha\ emission peaks is intermediate between that of Lyman-alpha emitters and radio galaxies, implying that the Ly\alpha\ emission is predominantly due to ionizing radiation from the AGN. Galaxies neighboring the quasar host are likely responsible for the majority (> 75%) of these DLAs, with only a minority (< 25%) arising from HI clouds located in the AGN host galaxy.
    Astronomy and Astrophysics 08/2013; · 5.08 Impact Factor
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    ABSTRACT: In the context of the study of the Integrated Sachs Wolfe effect (ISW), we construct a template of the projected density distribution up to $z\simeq 0.7$ by using the Luminous Galaxies (LGs) from the Sloan Digital Sky Survey DR8. We use a photo-z catalogue trained with more than a hundred thousand galaxies from BOSS in the SDSS DR8 imaging area. We consider two different LG samples whose selection matches that of SDSS-III/BOSS: the LOWZ sample ($z\in [0.15,0.5]$) and the CMASS sample ($z\in[0.4,0.7]$). When building the LG density maps we use the information from star density, survey footprint, seeing conditions, sky emission, dust extinction and airmass to explore the impact of these artifacts on the two LG samples. In agreement with previous studies, we find that the CMASS sample is particularly sensitive to Galactic stars, which dominate the contribution to the auto-angular power spectrum below $\ell=7$. Other potential systematics affect mostly the low multipole range ($\ell\in[2,7]$), but leave fluctuations on smaller scales practically unchanged. The resulting power spectra in the multipole range $\ell\in[2,100]$ for the LOWZ, CMASS and LOWZ+CMASS samples are compatible with linear $\Lambda$CDM expectations and constant bias values of $b=1.98 \pm 0.11$, $2.08\pm0.14$ and $1.88\pm 0.11$, respectively, with no traces of non-Gaussianity: $f_{\rm NL}^{\rm local}=59\pm 75$ at 95% confidence level for the full LOWZ+CMASS sample in the range $\ell\in[4,100]$. After cross-correlating WMAP-9yr data with the LOWZ+CMASS LG density field, the ISW signal is detected at the level of 1.62--1.69$\,\sigma$. While this result is in close agreement with predictions from Monte Carlo simulations in the concordance $\Lambda$CDM model, it cannot rule out by itself an Einstein-de Sitter scenario, and has a moderately low signal compared to previous studies conducted on subsets of this LG sample.
    Monthly Notices of the Royal Astronomical Society 03/2013; · 5.52 Impact Factor
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    ABSTRACT: We present a fast method of producing mock galaxy catalogues that can be used to compute covariance matrices of large-scale clustering measurements and test the methods of analysis. Our method populates a 2nd-order Lagrangian Perturbation Theory (2LPT) matter field, where we calibrate masses of dark matter halos by detailed comparisons with N-body simulations. We demonstrate the clustering of halos is recovered at ~10 per cent accuracy. We populate halos with mock galaxies using a Halo Occupation Distribution (HOD) prescription, which has been calibrated to reproduce the clustering measurements on scales between 30 and 80 Mpc/h. We compare the sample covariance matrix from our mocks with analytic estimates, and discuss differences. We have used this method to make catalogues corresponding to Data Release 9 of the Baryon Oscillation Spectroscopic Survey (BOSS),producing 600 mock catalogues of the "CMASS" galaxy sample. These mocks enabled detailed tests of methods and errors that formed an integral part of companion analyses of these galaxy data.
    Monthly Notices of the Royal Astronomical Society 03/2012; 428(2). · 5.52 Impact Factor
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    ABSTRACT: We study Milky Way kinematics using a sample of 18.8 million main-sequence stars with r < 20 and proper-motion measurements derived from Sloan Digital Sky Survey (SDSS) and POSS astrometry, including ~170,000 stars with radial-velocity measurements from the SDSS spectroscopic survey. Distances to stars are determined using a photometric-parallax relation, covering a distance range from ~100 pc to 10 kpc over a quarter of the sky at high Galactic latitudes (|b|>20°). We find that in the region defined by 1 kpc <Z< 5 kpc and 3 kpc <R< 13 kpc, the rotational velocity for disk stars smoothly decreases, and all three components of the velocity dispersion increase, with distance from the Galactic plane. In contrast, the velocity ellipsoid for halo stars is aligned with a spherical coordinate system and appears to be spatially invariant within the probed volume. The velocity distribution of nearby (Z < 1 kpc) K/M stars is complex, and cannot be described by a standard Schwarzschild ellipsoid. For stars in a distance-limited subsample of stars (<100 pc), we detect a multi-modal velocity distribution consistent with that seen by HIPPARCOS. This strong non-Gaussianity significantly affects the measurements of the velocity-ellipsoid tilt and vertex deviation when using the Schwarzschild approximation. We develop and test a simple descriptive model for the overall kinematic behavior that captures these features over most of the probed volume, and can be used to search for substructure in kinematic and metallicity space. We use this model to predict further improvements in kinematic mapping of the Galaxy expected from Gaia and the Large Synoptic Survey Telescope.
    The Astrophysical Journal 05/2010; · 6.73 Impact Factor
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    ABSTRACT: 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 nonuniform 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, Σ(R) Rα, in the volume-limited SDSS sample is α -1.7 ± 0.1, independent of the galaxy and satellite luminosities. Comparison with ΛCDM 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 h-1 kpc. 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.
    The Astrophysical Journal 12/2008; 647(1):86. · 6.73 Impact Factor
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    ABSTRACT: Using a sample of over 25,000 spectroscopically confirmed quasars from the Sloan Digital Sky Survey, we show how quasar variability in the rest-frame optical/UV regime depends on rest-frame time lag, luminosity, rest wavelength, redshift, the presence of radio and X-ray emission, and the presence of broad absorption line systems. Imaging photometry is compared with three-band spectrophotometry obtained at later epochs spanning time lags up to about 2 yr. The large sample size and wide range of parameter values allow the dependence of variability to be isolated as a function of many independent parameters. The time dependence of variability (the structure function) is well fitted by a single power law with an index γ = 0.246 ± 0.008, on timescales from days to years. There is an anticorrelation of variability amplitude with rest wavelength—e.g., quasars are about twice as variable at 1000 Å as at 6000 Å—and quasars are systematically bluer when brighter at all redshifts. There is a strong anticorrelation of variability with quasar luminosity—variability amplitude decreases by a factor of about 4 when luminosity increases by a factor of 100. There is also a significant positive correlation of variability amplitude with redshift, indicating evolution of the quasar population or the variability mechanism. We parameterize all of these relationships. Quasars with ROSAT All-Sky Survey X-ray detections are significantly more variable (at optical/UV wavelengths) than those without, and radio-loud quasars are marginally more variable than their radio-quiet counterparts. We find no significant difference in the variability of quasars with and without broad absorption line troughs. Currently, no models of quasar variability address more than a few of these relationships. Models involving multiple discrete events or gravitational microlensing are unlikely by themselves to account for the data. So-called accretion disk instability models are promising, but more quantitative predictions are needed.
    The Astrophysical Journal 12/2008; 601(2):692. · 6.73 Impact Factor
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    ABSTRACT: We study the recently discovered gravitational lens SDSS J1004+4112, the first quasar lensed by a cluster of galaxies. It consists of four images with a maximum separation of 1462. The system was selected from the photometric data of the Sloan Digital Sky Survey (SDSS) and has been confirmed as a lensed quasar at z = 1.734 on the basis of deep imaging and spectroscopic follow-up observations. We present color-magnitude relations for galaxies near the lens plus spectroscopy of three central cluster members, which unambiguously confirm that a cluster at z = 0.68 is responsible for the large image separation. We find a wide range of lens models consistent with the data, and despite considerable diversity they suggest four general conclusions: (1) the brightest cluster galaxy and the center of the cluster potential well appear to be offset by several kiloparsecs; (2) the cluster mass distribution must be elongated in the north-south direction, which is consistent with the observed distribution of cluster galaxies; (3) the inference of a large tidal shear (~0.2) suggests significant substructure in the cluster; and (4) enormous uncertainty in the predicted time delays between the images means that measuring the delays would greatly improve constraints on the models. We also compute the probability of such large-separation lensing in the SDSS quasar sample on the basis of the cold dark matter model. The lack of large-separation lenses in previous surveys and the discovery of one in SDSS together imply a mass fluctuation normalization σ8 = 1.0 (95% confidence) if cluster dark matter halos have an inner density profile ρ r-1.5. Shallower profiles would require higher values of σ8. Although the statistical conclusion might be somewhat dependent on the degree of the complexity of the lens potential, the discovery of SDSS J1004+4112 is consistent with the predictions of the abundance of cluster-scale halos in the cold dark matter scenario.
    The Astrophysical Journal 12/2008; 605(1):78. · 6.73 Impact Factor
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    ABSTRACT: We report the discovery of two doubly imaged quasars, SDSS J100128.61+502756.9 and SDSS J120629.65+433217.6, at redshifts of 1.838 and 1.789, and with image separations of 286 and 290, respectively. The objects were selected as lens candidates from the Sloan Digital Sky Survey (SDSS). Based on the identical nature of the spectra of the two quasars in each pair and the identification of the lens galaxies, we conclude that the objects are gravitational lenses. The lenses are complicated; in both systems there are several galaxies in the fields very close to the quasars, in addition to the lens galaxies themselves. The lens modeling implies that these nearby galaxies contribute significantly to the lens potentials. On larger scales, we have detected an enhancement in the galaxy density near SDSS J100128.61+502756.9. The number of lenses with image separation of ~3'' in the SDSS already exceeds the prediction of simple theoretical models based on the standard Λ-dominated cosmology and observed velocity function of galaxies.
    The Astrophysical Journal 12/2008; 622(1):106. · 6.73 Impact Factor
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    ABSTRACT: Using effective temperature and metallicity derived from SDSS spectra for ~60,000 F and G type main sequence stars (0.2<g-r<0.6), we develop polynomial models for estimating these parameters from the SDSS u-g and g-r colors. We apply this method to SDSS photometric data for about 2 million F/G stars and measure the unbiased metallicity distribution for a complete volume-limited sample of stars at distances between 500 pc and 8 kpc. The metallicity distribution can be exquisitely modeled using two components with a spatially varying number ratio, that correspond to disk and halo. The two components also possess the kinematics expected for disk and halo stars. The metallicity of the halo component is spatially invariant, while the median disk metallicity smoothly decreases with distance from the Galactic plane from -0.6 at 500 pc to -0.8 beyond several kpc. The absence of a correlation between metallicity and kinematics for disk stars is in a conflict with the traditional decomposition in terms of thin and thick disks. We detect coherent substructures in the kinematics--metallicity space, such as the Monoceros stream, which rotates faster than the LSR, and has a median metallicity of [Fe/H]=-0.96, with an rms scatter of only ~0.15 dex. We extrapolate our results to the performance expected from the Large Synoptic Survey Telescope (LSST) and estimate that the LSST will obtain metallicity measurements accurate to 0.2 dex or better, with proper motion measurements accurate to ~0.2 mas/yr, for about 200 million F/G dwarf stars within a distance limit of ~100 kpc (g<23.5). [abridged]
    The Astrophysical Journal 05/2008; · 6.73 Impact Factor
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    ABSTRACT: We positionally correlate known asteroids with a sample of ~18,000 asteroids detected by the Sloan Digital Sky Survey (SDSS). We find 2641 unique matches, which represent the largest sample of asteroids with both accurate multicolor photometry and known orbital parameters. The matched objects are predominantly bright and demonstrate that the SDSS photometric pipeline recovers ~90% of the known asteroids in the observed region. For the recovered asteroids, we find a large offset (~0.4 mag) between Johnson V magnitudes derived from SDSS photometry and the predicted magnitudes. This offset varies with the asteroid color, from 0.34 mag for blue asteroids to 0.44 mag for red asteroids, and is probably caused by the use of unfiltered CCD observations in the majority of recent asteroid surveys. This systematic photometric error leads to an overestimate of the number of asteroids brighter than a given absolute magnitude limit by a factor of ~1.7. The distribution of the matched asteroids in orbital parameter space indicates strong color segregation. We confirm that some families are dominated by a single asteroid type (e.g., the Koronis family by red asteroids and the Themis family by blue asteroids), while others appear to be a mixture of blue and red objects (e.g., the Nysa-Polana family). Asteroids with the bluest i*-z* colors, which can be associated with the Vesta family, show particularly striking localization in orbital parameter space.
    The Astronomical Journal 12/2007; 124(3):1776. · 4.97 Impact Factor
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    ABSTRACT: We discuss the optical and radio properties of ~30,000 FIRST (radio, 20 cm, sensitive to 1 mJy) sources positionally associated within 15 with a Sloan Digital Sky Survey (SDSS) (optical, sensitive to r* ~ 22.2) source in 1230 deg2 of sky. The matched sample represents ~30% of the 108,000 FIRST sources and 0.1% of the 2.5 × 107 SDSS sources in the studied region. SDSS spectra are available for 4300 galaxies and 1154 quasars from the matched sample and for a control sample of 140,000 galaxies and 20,000 quasars in 1030 deg2 of sky. Here we analyze only core sources, which dominate the sample; the fraction of SDSS-FIRST sources with complex radio morphology is determined to be less than 10%. This large and unbiased catalog of optical identifications provides much firmer statistical footing for existing results and allows several new findings. The majority (83%) of the FIRST sources identified with an SDSS source brighter than r* = 21 are optically resolved; the fraction of resolved objects among the matched sources is a function of the radio flux, increasing from ~50% at the bright end to ~90% at the FIRST faint limit. Nearly all optically unresolved radio sources have nonstellar colors indicative of quasars. We estimate an upper limit of ~5% for the fraction of quasars with broadband optical colors indistinguishable from those of stars. The distribution of quasars in the radio flux–optical flux plane suggests the existence of the "quasar radio dichotomy"; 8% ± 1% of all quasars with i* < 18.5 are radio-loud, and this fraction seems independent of redshift and optical luminosity. The radio-loud quasars have a redder median color by 0.08 ± 0.02 mag, and show a 3 times larger fraction of objects with extremely red colors. FIRST galaxies represent 5% of all SDSS galaxies with r* < 17.5, and 1% for r* < 20, and are dominated by red (u*-r* > 2.22) galaxies, especially those with r* > 17.5. Magnitude- and redshift-limited samples show that radio galaxies have a different optical luminosity distribution than nonradio galaxies selected by the same criteria; when galaxies are further separated by their colors, this result remains valid for both blue and red galaxies. For a given optical luminosity and redshift, the observed optical colors of radio galaxies are indistinguishable from those of all SDSS galaxies selected by identical criteria. The distributions of radio-to-optical flux ratio are similar for blue and red galaxies in redshift-limited samples; this similarity implies that the difference in their luminosity functions and resulting selection effects are the dominant cause for the preponderance of red radio galaxies in flux-limited samples. The fraction of radio galaxies whose emission-line ratios indicate an AGN (30%), rather than starburst, origin is 6 times larger than the corresponding fraction for all SDSS galaxies (r* < 17.5). We confirm that the AGN-to-starburst galaxy number ratio increases with radio flux and find that radio emission from AGNs is more concentrated than radio emission from starburst galaxies.
    The Astronomical Journal 12/2007; 124(5):2364. · 4.97 Impact Factor
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    ABSTRACT: We discuss measurements of the properties of ~13,000 asteroids detected in 500 deg2 of sky in the Sloan Digital Sky Survey (SDSS) commissioning data. The moving objects are detected in the magnitude range 14 < r* < 21.5, with a baseline of ~5 minutes, resulting in typical velocity errors of ~3%. Extensive tests show that the sample is at least 98% complete, with a contamination rate of less than 3%. We find that the size distribution of asteroids resembles a broken power law, independent of the heliocentric distance: D-2.3 for 0.4 km D 5 km, and D-4 for 5 km D 40 km. As a consequence of this break, the number of asteroids with r* < 21.5 is 10 times smaller than predicted by extrapolating the power-law relation observed for brighter asteroids (r* 18). The observed counts imply that there are about 670,000 objects with D > 1 km in the asteroid belt, or up to 3 times less than previous estimates. The revised best estimate for the impact rate of the so-called "killer" asteroids (D > 1 km) is about 1 every 500,000 yr, uncertain to within a factor of 2. We predict that by its completion SDSS will obtain about 100,000 near simultaneous five-band measurements for a subset drawn from 340,000 asteroids brighter than r* < 21.5 at opposition. Only about a third of these asteroids have been previously observed, and usually in just one band. The distribution of main-belt asteroids in the four-dimensional SDSS color space is bimodal, and the two groups can be associated with S- (rocky) and C- (carbonaceous) type asteroids. A strong bimodality is also seen in the heliocentric distribution of asteroids: the inner belt is dominated by S-type asteroids centered at R ~ 2.8 AU, while C-type asteroids, centered at R ~ 3.2 AU, dominate the outer belt. The median color of each class becomes bluer by about 0.03 mag AU-1 as the heliocentric distance increases. The observed number ratio of S and C asteroids in a sample with r* < 21.5 is 1.5 : 1, while in a sample limited by absolute magnitude it changes from 4 : 1 at 2 AU, to 1 : 3 at 3.5 AU. In a size-limited sample with D > 1 km, the number ratio of S and C asteroids in the entire main belt is 1 : 2.3. The colors of Hungarias, Mars crossers, and near-Earth objects, selected by their velocity vectors, are more similar to the C-type than to S-type asteroids. In about 100 deg2 of sky along the celestial equator observed twice 2 days apart, we find one plausible Kuiper belt object (KBO) candidate, in agreement with the expected KBO surface density. The colors of the KBO candidate are significantly redder than the asteroid colors, in agreement with colors of known KBOs. We explore the possibility that SDSS data can be used to search for very red, previously uncataloged asteroids observed by 2MASS, by extracting objects without SDSS counterparts. We do not find evidence for a significant population of such objects; their contribution is no more than 10% of the asteroid population.
    The Astronomical Journal 12/2007; 122(5):2749. · 4.97 Impact Factor
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    ABSTRACT: We present new VLT spectroscopic observations of the most distant quasar known, SDSS J1030+0524 at z = 6.28, which was recently discovered by the Sloan Digital Sky Survey. We confirm the presence of a complete Gunn-Peterson trough caused by neutral hydrogen in the intergalactic medium. There is no detectable flux over the wavelength range from 8450 to 8710 Å. We set a stronger limit on the drop of the flux level blueward of the Lyα line: a factor of more than 200. Below 8450 Å the spectrum shows a rise in flux, with a large fraction (>60%) of the total emission produced by a few narrow features of transmitted flux. We discuss the proximity effect around this quasar, with the presence of transmitted flux with many absorption features in a region of about 23 h-1 comoving Mpc. If we assume that the surrounding medium is completely neutral, the size of this region would imply a quasar lifetime of ~1.3 × 107 yr. We also present near-IR spectroscopy of both SDSS J1030+0524 and SDSS J1306+05, the second most distant quasar known, at redshift 6.0. We combine measurements of the C IV line and limits on the He II emission from the near-IR spectra with the N V line measurements from the optical spectra to derive the metal abundances of these early quasar environments. The results are indistinguishable from those of lower redshift quasars and indicate little or no evolution in the metal abundances from z ~ 6 to 2. The line ratios suggest supersolar metallicities, implying that the first stars around the quasars must have formed at least a few hundreds of megayears prior to the observation, i.e., at redshifts higher than 8.
    The Astronomical Journal 12/2007; 123(5):2151. · 4.97 Impact Factor
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    ABSTRACT: We present the 3D real-space clustering power spectrum of a sample of ∼600 000 luminous red galaxies measured by the Sloan Digital Sky Survey, using photometric redshifts. These galaxies are old, elliptical systems with strong 4000-Å breaks, and have accurate photometric redshifts with an average error of Δz= 0.03. This sample of galaxies ranges from redshift z= 0.2 to 0.6 over 3528 deg2 of the sky, probing a volume of 1.5 h−3 Gpc3, making it the largest volume ever used for galaxy clustering measurements. We measure the angular clustering power spectrum in eight redshift slices and use well-calibrated redshift distributions to combine these into a high-precision 3D real-space power spectrum from k= 0.005 to k= 1 h Mpc−1. We detect power on gigaparsec scales, beyond the turnover in the matter power spectrum, at a ∼2σ significance for k < 0.01 h Mpc−1, increasing to 5.5σ for k < 0.02 h Mpc−1. This detection of power is on scales significantly larger than those accessible to current spectroscopic redshift surveys. We also find evidence for baryonic oscillations, both in the power spectrum, as well as in fits to the baryon density, at a 2.5 σ confidence level. The large volume and resulting small statistical errors on the power spectrum allow us to constrain both the amplitude and the scale dependence of the galaxy bias in cosmological fits. The statistical power of these data to constrain cosmology is ∼1.7 times better than previous clustering analyses. Varying the matter density and baryon fraction, we find ΩM= 0.30 ± 0.03, and Ωb/ΩM= 0.18 ± 0.04, for a fixed Hubble constant of 70 km s−1 Mpc−1 and a scale-invariant spectrum of initial perturbations. The detection of baryonic oscillations also allows us to measure the comoving distance to z= 0.5; we find a best-fitting distance of 1.73 ± 0.12 Gpc, corresponding to a 6.5 per cent error on the distance. These results demonstrate the ability to make precise clustering measurements with photometric surveys.
    Monthly Notices of the Royal Astronomical Society 06/2007; 378(3):852 - 872. · 5.52 Impact Factor
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    ABSTRACT: We present results of a measurement of the shape of the density profile of galaxy groups and clusters traced by 43 335 Luminous Red Galaxies (LRGs) with spectroscopic redshifts from the Sloan Digital Sky Survey (SDSS). The galaxies are selected such that they are the brightest within a cylindrical aperture, split into two luminosity samples and modelled as the sum of stellar and dark matter components. We present a detailed investigation of many possible systematic effects that could contaminate our signal and develop methods to remove them, including a detected intrinsic alignment for galaxies within 100 h−1 kpc of LRGs which we remove using photometric redshift information. The resulting lensing signal is consistent with NFW (Navarro, Frenk & White) profile dark matter haloes; the singular isothermal sphere (SIS) profile is ruled out at the 96 (conservatively) and 99.96 per cent confidence level (CL) for the fainter and brighter lens samples (respectively) when we fit using lensing data between 0.4 and 2 h−1 Mpc with total signal-to-noise ratio of 19 and 25 for the two lens samples. The lensing signal amplitude suggests that the faint and bright sample galaxies typically reside in haloes of mass (2.9 ± 0.4) × 1013 and (6.7 ± 0.8) × 1013 h−1 M⊙, respectively, in good agreement with predictions based on halo spatial density with normalization lower than the ‘concordance’σ8= 0.9. When fitting for the concentration parameter in the NFW profile, we find c= 5.0 ± 0.6 (stat) ± 1 (sys), and c= 5.6 ± 0.6 (stat) ± 1 (sys) for the faint and bright samples, consistent with Λ cold dark matter (CDM) simulations. We also split the bright sample further to determine masses and concentrations for cluster-mass haloes, finding mass (1.3 ± 0.2) × 1014 h−1 M⊙ for the sample of LRGs brighter than −22.6 in r. We establish that on average there is a correlation between the halo mass and central galaxy luminosity relation that scales as M∝L2.
    Monthly Notices of the Royal Astronomical Society 10/2006; 372(2):758 - 776. · 5.52 Impact Factor
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    ABSTRACT: We present the results of attempts to detect the ellipticity of dark matter haloes using galaxy–galaxy weak lensing with Sloan Digital Sky Survey (SDSS) data. We use 2 020 256 galaxies brighter than r= 19 with photometric redshifts (divided into colour and luminosity subsamples) as lenses and 31 697 869 source galaxies. We search for and identify several signal contaminants, which if not removed lead to a spurious detection. These include systematic shear that leads to a slight spurious alignment of lens and source ellipticities, intrinsic alignments (due to contamination of the source sample by physically associated lens–source pairs), and anisotropic magnification bias. We develop methods that allow us to remove these contaminants to the signal. We split the analysis into blue (spiral) and red (elliptical) galaxies. Assuming Gaussian errors as in previous work and a power-law profile, we find fh=eh/eg= 0.1 ± 0.06 for red galaxies and −0.8 ± 0.4 for blue galaxies, using transverse separations of 20–300 h−1 kpc, averaged over luminosity. Inclusion of the more realistic non-Gaussian error distributions and of the Navarro–Frenk–White (NFW) density profile (which predicts much smaller ellipticity of the shear for scales above the scale radius) yields 0.60 ± 0.38 for ellipticals and −1.4+1.7−2.0 for spirals. While there is no concrete detection of alignment in either case, there is a suggestion in the data of a positive alignment in the brightest lens sample of ellipticals. Our results appear to be mildly inconsistent with a previously reported detection by Hoekstra, Yee & Gladders, but more data and further tests are needed to clarify whether the discrepancy is real or a consequence of differences in the lens galaxy samples used and analysis methods.
    Monthly Notices of the Royal Astronomical Society 07/2006; 370(2):1008 - 1024. · 5.52 Impact Factor
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    ABSTRACT: The relationship between galaxies and dark matter (DM) can be characterized by the halo mass of the central galaxy and the fraction of galaxies that are satellites. Here, we present observational constraints from the Sloan Digital Sky Survey on these quantities as a function of r-band luminosity and stellar mass using galaxy–galaxy weak lensing, with a total of 351 507 lenses. We use stellar masses derived from spectroscopy and virial halo masses derived from weak gravitational lensing to determine the efficiency with which baryons in the halo of the central galaxy have been converted into stars. We find that an L* galaxy with a stellar mass of 6 × 1010 M⊙ is hosted by a halo with mass of 1.4 × 1012 h−1 M⊙, independent of morphology, yielding baryon conversion efficiencies of 17+10−5 per cent (early-types) and 16+15−6 per cent (late-types) at the 95 per cent confidence level (statistical, not including systematic uncertainty due to assumption of a universal initial mass function). We find that for a given stellar mass, the halo mass is independent of morphology below Mstellar= 1011 M⊙, in contrast to typically a factor of 2 difference in halo mass between ellipticals and spirals at a fixed luminosity. This suggests that stellar mass is a good proxy for halo mass in this range and should be used preferentially whenever a halo mass selected sample is needed. For higher stellar masses, the conversion efficiency is a declining function of stellar mass, and the differences in halo mass between early- and late-types become larger, reflecting the fact that most group and cluster haloes with masses above 1013 M⊙ host ellipticals at the centre, while even the brightest central spirals are hosted by haloes of mass below 1013 M⊙. We find that the fraction of spirals that are satellites is roughly 10–15 per cent independent of stellar mass or luminosity, while for ellipticals this fraction decreases with stellar mass from 50 per cent at 1010 M⊙ to 10 per cent at 3 × 1011 M⊙ or 20 per cent at the maximum luminosity considered. We split the elliptical sample by local density, and find that at a given luminosity there is no difference in the signal on scales below 100 h−1 kpc between high- and low-density regions, suggesting that tidal stripping inside large haloes does not remove most of the DM from the early-type satellites. This result is dominated by haloes in the mass range 1013–1014 h−1 M⊙, and is an average over all separations from the group or cluster centre.
    Monthly Notices of the Royal Astronomical Society 05/2006; 368(2):715 - 731. · 5.52 Impact Factor
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    ABSTRACT: The power spectrum of weak lensing shear caused by large-scale structure is an emerging tool for precision cosmology, in particular for measuring the effects of dark energy on the growth of structure at low redshift. One potential source of systematic error is intrinsic alignments of ellipticities of neighbouring galaxies [the intrinsic ellipticity—intrinsic ellipticity (II) correlation] that could mimic the correlations due to lensing. A related possibility pointed out by Hirata & Seljak is correlation between the intrinsic ellipticities of galaxies and the density field responsible for gravitational lensing shear [the gravitational shear—intrinsic ellipticity (GI) correlation]. We present constraints on both the II and GI correlations using 265 908 spectroscopic galaxies from the Sloan Digital Sky Survey (SDSS) and using galaxies as tracers of the mass in the case of the GI analysis. The availability of redshifts in the SDSS allows us to select galaxies at small radial separations, which both reduces noise in the intrinsic alignment measurement and suppresses galaxy–galaxy lensing (which otherwise swamps the GI correlation). While we find no detection of the II correlation, our results are none the less statistically consistent with recent detections found using the SuperCOSMOS survey. Extrapolation of these limits to cosmic shear surveys at z∼ 1 suggests that the II correlation is unlikely to have been a significant source of error for current measurements of σ8 with ∼ 10 per cent accuracy, but may still be an issue for future surveys with projected statistical errors below the 1 per cent level unless eliminated using photometric redshifts. In contrast, we have a clear detection of GI correlation in galaxies brighter than L* that persists to the largest scales probed (60 h−1 Mpc) and with a sign predicted by theoretical models. This correlation could cause the existing lensing surveys at z∼ 1 to underestimate the linear amplitude of fluctuations by as much as 20 per cent depending on the source sample used, while for surveys at z∼ 0.5 the underestimation may reach 30 per cent. The GI contamination is dominated by the brightest galaxies, possibly due to the alignment of brightest cluster galaxies (BCGs) with the cluster ellipticity due to anisotropic infall along filaments, although other sources of contamination cannot be excluded at this point. We propose that cosmic shear surveys should consider rejection of BCGs from their source catalogues as a test for GI contamination. Future high-precision weak lensing surveys must develop methods to search for and remove this contamination if they are to achieve their promise.
    Monthly Notices of the Royal Astronomical Society 02/2006; 367(2):611 - 626. · 5.52 Impact Factor
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    ABSTRACT: Only seven radio-quiet isolated neutron stars (INSs) emitting thermal X rays are known, a sample that has yet to definitively address such fundamental issues as the equation of state of degenerate neutron matter. We describe a selection algorithm based on a cross-correlation of the ROSAT All-Sky Survey (RASS) and the Sloan Digital Sky Survey (SDSS) that identifies X-ray error circles devoid of plausible optical counterparts to the SDSS g~22 magnitudes limit. We quantitatively characterize these error circles as optically blank; they may host INSs or other similarly exotic X-ray sources such as radio-quiet BL Lacs, obscured AGN, etc. Our search is an order of magnitude more selective than previous searches for optically blank RASS error circles, and excludes the 99.9% of error circles that contain more common X-ray-emitting subclasses. We find 11 candidates, nine of which are new. While our search is designed to find the best INS candidates and not to produce a complete list of INSs in the RASS, it is reassuring that our number of candidates is consistent with predictions from INS population models. Further X-ray observations will obtain pinpoint positions and determine whether these sources are entirely optically blank at g~22, supporting the presence of likely isolated neutron stars and perhaps enabling detailed follow-up studies of neutron star physics.
    The Astronomical Journal 12/2005; · 4.97 Impact Factor

Publication Stats

2k Citations
146.39 Total Impact Points

Institutions

  • 2010
    • Lawrence Berkeley National Laboratory
      • Physics Division
      Berkeley, California, United States
  • 2006
    • Abdus Salam International Centre for Theoretical Physics
      Trst, Friuli Venezia Giulia, Italy
    • University of Texas at Dallas
      • Physics
      Dallas, TX, United States
  • 2005
    • University of Pennsylvania
      • Department of Physics and Astronomy
      Philadelphia, PA, United States
    • Pennsylvania State University
      • Department of Astronomy and Astrophysics
      University Park, Maryland, United States
  • 2004
    • The University of Tokyo
      • Institute for Cosmic Ray Research
      Edo, Tōkyō, Japan