David H. Weinberg

University of Colorado, Denver, Colorado, United States

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Publications (351)1290.69 Total impact

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    ABSTRACT: We employ the first two years of data from the near-infrared, high-resolution SDSS-III/APOGEE spectroscopic survey to investigate the distribution of metallicity and alpha-element abundances of stars over a large part of the Milky Way disk. Using a sample of ~10,000 kinematically-unbiased red-clump stars with ~5% distance accuracy as tracers, the [alpha/Fe] vs. [Fe/H] distribution of this sample exhibits a bimodality in [alpha/Fe] at intermediate metallicities, -0.9<[Fe/H]<-0.2, but at higher metallicities ([Fe/H]=+0.2) the two sequences smoothly merge. We investigate the effects of the APOGEE selection function and volume filling fraction and find that these have little qualitative impact on the alpha-element abundance patterns. The described abundance pattern is found throughout the range 5<R<11 kpc and 0<|Z|<2 kpc across the Galaxy. The [alpha/Fe] trend of the high-alpha sequence is surprisingly constant throughout the Galaxy, with little variation from region to region (~10%). Using simple galactic chemical evolution models we derive an average star formation efficiency (SFE) in the high-alpha sequence of ~4.5E-10 1/yr, which is quite close to the nearly-constant value found in molecular-gas-dominated regions of nearby spirals. This result suggests that the early evolution of the Milky Way disk was characterized by stars that shared a similar star formation history and were formed in a well-mixed, turbulent, and molecular-dominated ISM with a gas consumption timescale (1/SFE) of ~2 Gyr. Finally, while the two alpha-element sequences in the inner Galaxy can be explained by a single chemical evolutionary track this cannot hold in the outer Galaxy, requiring instead a mix of two or more populations with distinct enrichment histories.
    09/2014;
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    ABSTRACT: We present the measurements and modelling of the projected and redshift-space clustering of CMASS galaxies in the Sloan Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey Data Release 11. For a volume-limited luminous red galaxy sample in the redshift range of $0.48<z<0.55$, we perform halo occupation distribution modelling of the small- and intermediate-scale ($0.1$--$60h^{-1}{\rm {Mpc}}$) projected and redshift-space two-point correlation functions, with an accurate model built on high resolution $N$-body simulations. To interpret the measured redshift-space distortions, the distribution of galaxy velocities must differ from that of the dark matter inside haloes of $\sim 10^{13}$--$10^{14}h^{-1}{\rm M_{\odot}}$, i.e. the data require the existence of galaxy velocity bias. Most notably, central galaxies on average are not at rest with respect to the core of their host haloes (defined by the inner 25% of particles around the halo potential minimum), but rather move around it with a 1D velocity dispersion of $0.22^{+0.03}_{-0.04}$ times that of the dark matter, implying a spatial offset from the centre at the level of $\lesssim$1% of the halo virial radius. The luminous satellite galaxies move more slowly than the dark matter, with velocities $0.86^{+0.08}_{-0.03}$ times those of the dark matter, which suggests that the velocity and spatial distributions of these satellites cannot both be unbiased. The constraints mainly arise from the Fingers-of-God effect at nonlinear scales and the smoothing to the Kaiser effect in the translinear regime; the robustness of the results is demonstrated by a variety of tests. In addition, no clear evidence is found for a strong luminosity dependence of the velocity bias. We discuss the implications of the existence of galaxy velocity bias for investigations of galaxy formation and cosmology.
    07/2014;
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    ABSTRACT: We report new observations of circumgalactic gas from the COS-Dwarfs survey, a systematic investigation of the gaseous halos around 43 low-mass z $\leq$ 0.1 galaxies using background QSOs observed with the Cosmic Origins Spectrograph. From the projected 1D and 2D distribution of C IV absorption, we find that C IV absorption is detected out to ~ 0.5 R$_{vir}$ of the host galaxies. The C IV absorption strength falls off radially as a power law and beyond 0.5 R$_{vir}$, no C IV absorption is detected above our sensitivity limit of ~ 50-100 m$\AA$. We find a tentative correlation between detected C IV absorption strength and star formation, paralleling the strong correlation seen in highly ionized oxygen for L~L* galaxies by the COS-Halos survey. The data imply a large carbon reservoir in the CGM of these galaxies, corresponding to a minimum carbon mass of $\gtrsim$ 1.2$\times 10^6$ $M_\odot$ out to ~ 110 kpc. This mass is comparable to the carbon mass in the ISM and more than the carbon mass currently in stars of these galaxies. The C IV absorption seen around these sub-L* galaxies can account for almost two-thirds of all $W_r$> 100 m$\AA$ C IV absorption detected at low z. Comparing the C IV covering fraction with hydrodynamical simulations, we find that an energy-driven wind model is consistent with the observations whereas a wind model of constant velocity fails to reproduce the CGM or the galaxy properties.
    06/2014;
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    ABSTRACT: The Sloan Digital Sky Survey III's Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a high-resolution near-infrared spectroscopic survey covering all of the major components of the Galaxy, including the dust-obscured regions of the inner Milky Way disk and bulge. Here we present a sample of 10,352 likely red-clump stars (RC) from the first two years of APOGEE operations, selected based on their position in color-metallicity-surface-gravity-effective-temperature space using a new method calibrated using stellar-evolution models and high-quality asteroseismology data. The narrowness of the RC locus in color-metallicity-luminosity space allows us to assign distances to the stars with an accuracy of 5 to 10%. The sample extends to typical distances of about 3 kpc from the Sun, with some stars out to 8 kpc, and spans a volume of approximately 100 kpc^3 over 5 kpc <~ R <~ 14 kpc, |Z| <~ 2 kpc, and -15 deg <~ Galactocentric azimuth <~ 30 deg. The APOGEE red-clump (APOGEE-RC) catalog contains photometry from 2MASS, reddening estimates, distances, line-of-sight velocities, stellar parameters and elemental abundances determined from the high-resolution APOGEE spectra, and matches to major proper motion catalogs. We determine the survey selection function for this data set and discuss how the RC selection samples the underlying stellar populations. We use this sample to limit any azimuthal variations in the median metallicity within the ~45 degree-wide azimuthal region covered by the current sample to be <= 0.02 dex, which is more than an order of magnitude smaller than the radial metallicity gradient. This result constrains coherent non-axisymmetric flows within a few kpc from the Sun.
    05/2014;
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    ABSTRACT: The Ly$\alpha$ forest flux probability distribution function (PDF) is an established probe of the intergalactic medium (IGM) astrophysics, especially the temperature-density relationship of the IGM. We measure the flux PDF from 3393 Baryon Oscillations Spectroscopic Survey (BOSS) quasars from SDSS Data Release 9, and compare with mock spectra that include careful modeling of the noise, continuum, and astrophysical uncertainties. The BOSS flux PDFs, measured at $\langle z \rangle = [2.3,2.6,3.0]$, are compared with PDFs created from mock spectra drawn from a suite of hydrodynamical simulations that sample the IGM temperature-density relationship, $\gamma$, and temperature at mean-density, $T_0$, where $T(\Delta) = T_0 \Delta^{\gamma-1}$. We find that a significant population of partial Lyman-limit systems with a column-density distribution slope of $\beta_\mathrm{pLLS} \sim -2$ are required to explain the data at the low-flux end of flux PDF, while uncertainties in the mean \lya\ forest transmission affect the high-flux end. After modelling the LLSs and marginalizing over mean-transmission uncertainties, we find that $\gamma=1.6$ best describes the data over our entire redshift range, although constraints on $T_0$ are affected by systematic uncertainties. Isothermal or inverted temperature-density relationships ($\gamma \leq 1$) are disfavored at a significance of over 4$\sigma$.
    05/2014;
  • 04/2014;
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    ABSTRACT: We examine the statistics of the low-redshift Lyman-alpha forest from smoothed particle hydrodynamic simulations in light of recent improvements in the estimated evolution of the cosmic ultraviolet background (UVB) and recent observations from the Cosmic Origins Spectrograph (COS). We find that the value of the metagalactic photoionization rate required by our simulations to match the observed properties of the low-redshift Lyman-alpha forest is a factor of 5 larger than the value predicted by state-of-the art models for the evolution of this quantity. This mismatch results in the mean flux decrement of the Lyman-alpha forest being underpredicted by at least a factor of 2 (a 10-sigma discrepancy with observations) and a column density distribution of Lyman-alpha forest absorbers systematically and significantly elevated compared to observations over nearly two decades in column density. We examine potential resolutions to this mismatch and find that either conventional sources of ionizing photons (galaxies and quasars) must be significantly elevated relative to current observational estimates or our theoretical understanding of the low-redshift universe is in need of substantial revision.
    The Astrophysical Journal Letters 04/2014; 789(2). · 6.35 Impact Factor
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    ABSTRACT: We report a detection of the baryon acoustic oscillation (BAO) feature in the flux-correlation function of the Ly{\alpha} forest of high-redshift quasars with a statistical significance of five standard deviations. The study uses 137,562 quasars in the redshift range $2.1\le z \le 3.5$ from the Data Release 11 (DR11) of the Baryon Oscillation Spectroscopic Survey (BOSS) of SDSS-III. This sample contains three times the number of quasars used in previous studies. The measured position of the BAO peak determines the angular distance, $D_A(z=2.34)$ and expansion rate, $H(z=2.34)$, both on a scale set by the sound horizon at the drag epoch, $r_d$. We find $D_A/r_d=11.28\pm0.65(1\sigma)^{+2.8}_{-1.2}(2\sigma)$ and $D_H/r_d=9.18\pm0.28(1\sigma)\pm0.6(2\sigma)$ where $D_H=c/H$. The optimal combination, $\sim D_H^{0.7}D_A^{0.3}/r_d$ is determined with a precision of $\sim2\%$. For the value $r_d=147.4~{\rm Mpc}$, consistent with the CMB power spectrum measured by Planck, we find $D_A(z=2.34)=1662\pm96(1\sigma)~{\rm Mpc}$ and $H(z=2.34)=222\pm7(1\sigma)~{\rm km\,s^{-1}Mpc^{-1}}$. Tests with mock catalogs and variations of our analysis procedure have revealed no systematic uncertainties comparable to our statistical errors. Our results agree with the previously reported BAO measurement at the same redshift using the quasar-Ly{\alpha} forest cross-correlation. The auto-correlation and cross-correlation approaches are complementary because of the quite different impact of redshift-space distortion on the two measurements. The combined constraints from the two correlation functions imply values of $D_A/r_d$ and $D_H/r_d$ that are, respectively, 7% low and 7% high compared to the predictions of a flat $\Lambda$CDM cosmological model with the best-fit Planck parameters. With our estimated statistical errors, the significance of this discrepancy is $\approx 2.5\sigma$.
    04/2014;
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    ABSTRACT: We examine the star formation histories (SFHs) of galaxies in smoothed particle hydrodynamics (SPH) simulations, compare them to parametric models that are commonly used in fitting observed galaxy spectral energy distributions, and examine the efficacy of these parametric models as practical tools for recovering the physical parameters of galaxies. The commonly used tau-model, with SFR ~ exp(-t/tau), provides a poor match to the SFH of our SPH galaxies, with a mismatch between early and late star formation that leads to systematic errors in predicting colours and stellar mass-to-light ratios. A one-parameter lin-exp model, with SFR ~ t*exp(-t/tau), is much more successful on average, but it fails to match the late-time behavior of the bluest, most actively star-forming galaxies and the passive, "red and dead" galaxies. We introduce a 4-parameter model, which transitions from lin-exp to a linear ramp after a transition time, which describes our simulated galaxies very well. We test the ability of these parametrised models to recover (at z=0, 0.5, and 1) the stellar mass-to-light ratios, specific star formation rates, and stellar population ages from the galaxy colours, computed from the full SPH star formation histories using the FSPS code of Conroy et al. (2009). Fits with tau-models systematically overestimate M/L by ~ 0.2 dex, overestimate population ages by ~ 1-2 Gyr, and underestimate sSFR by ~ 0.05 dex. Fits with lin-exp are less biased on average, but the 4-parameter model yields the best results for the full range of galaxies. Marginalizing over the free parameters of the 4-parameter model leads to slightly larger statistical errors than 1-parameter fits but essentially removes all systematic biases, so this is our recommended procedure for fitting real galaxies.
    04/2014;
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    ABSTRACT: We analyze the physical conditions of the cool (T ~ 10^4 K) circumgalactic medium (CGM) using the COS-Halos suite of gas column density measurements taken along 38 quasar sightlines passing within 160 kpc of L ~ L* galaxies at z~0.2. These data are well described by simple photoionization models, with the gas highly ionized (n_HII/n_H > 99%) by the extragalactic ultraviolet background (EUVB). Scaling by estimates for the virial radius, R_vir, we show that the ionization state (tracked by the dimensionless ionization parameter, U) increases with distance from the host galaxy. This correlation has a power-law form of U = (0.006 +/- 0.003)(R/R_vir)^(0.8 +/- 0.3), with significant scatter. The ionization parameters imply a decreasing volume density profile n_ H = 10^(-4.2 +/- 0.25) (R/R_vir)^(-0.8 +/-0.3). Our derived gas volume densities are several orders of magnitude lower than predictions from standard two-phase models with a cool medium in pressure equilibrium with a hot, diffuse medium. Applying the ionization corrections to the HI column densities, we estimate a lower limit to the cool gas mass M_ CGMcool > 6.5 x 10^10 M_sun for the volume within R < R_vir. Allowing for an additional warm, OVI-traced phase, the CGM accounts for *at least* half of the baryons purported to be missing from galaxy dark matter halos.
    The Astrophysical Journal 03/2014; 792(1). · 6.73 Impact Factor
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    ABSTRACT: We analyze the dynamical evolution of stellar age cohorts, groups of stars with similar formation times, to determine the detailed structure formation history of the cosmological simulation of the formation of a disk galaxy similar to the Milky Way (the “Eris” simulation). There is a remarkably smooth correlation between structure and stellar age at z = 0, going from spheroidal distributions for the oldest stars to long, thin disks for the youngest populations. We find the velocity dispersion of a cohort increases monotonically with age. The smooth relationships between stellar age, structure, and dynamics seen at z = 0, which agree nicely with the observed properties of mono-abundance populations in the Milky Way, are largely established by the disk formation process. Stars continuously form as the initially spheroidal gas reservoir cools and contracts, increasing its rotational support and becomingly progressively longer and vertically thinner. Thus, the stellar disk forms “inside-out” radially and “upside-down” vertically.
    02/2014;
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    ABSTRACT: The past three decades have seen prodigious advances in astronomy and astrophysics. Beginning with the exploration of our solar system and continuing through the pioneering Explorers and Great Observatories of today, NASA missions have made essential contributions to these advances. This roadmap presents a science-driven 30-year vision for the future of NASA Astrophysics that builds on these achievements to address some of our most ancient and fundamental questions: Are we alone? How did we get here? How does the universe work? The search for the answers constitutes the Enduring Quests of this roadmap. Building on the priorities identified in New Worlds, New Horizons, we envision future science investigations laid out in three Eras, with each representing roughly ten years of mission development in a given field. The immediate Near-Term Era covers ongoing NASA-led activities and planned missions. This will be followed by the missions of the Formative Era, which will build on the preceding technological developments and scientific discoveries, with remarkable capabilities that will enable breakthroughs across the landscape of astrophysics. These will then lay the foundations for the Daring Visions of the Visionary Era: missions and explorations that will take us deep into unchartered scientific and technological terrain. The roadmap outlined herein will require the vision and wherewithal to undertake highly ambitious programs over the next 30 years. The discoveries that emerge will inspire generations of citizen scientists young and old, and inspire all of humanity for decades to come.
    01/2014;
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    ABSTRACT: We investigate the luminosity and colour dependence of clustering of CMASS galaxies in the Sloan Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey Tenth Data Release. The halo occupation distribution framework is adopted to model the projected two-point correlation function measurements on small and intermediate scales (from $0.02$ to $60\,h^{-1}{\rm {Mpc}}$) and to interpret the observed trends and infer the connection of galaxies to dark matter halos. We find that luminous red galaxies reside in massive halos of mass $M{\sim}10^{13}$--$10^{14}\,h^{-1}{\rm M_\odot}$ and more luminous galaxies are more clustered and hosted by more massive halos. The strong small-scale clustering requires a fraction of these galaxies to be satellites in massive halos, with the fraction at the level of 5--8 per cent and decreasing with luminosity. The characteristic mass of a halo hosting on average one satellite galaxy above a luminosity threshold is about a factor $8.7$ larger than that of a halo hosting a central galaxy above the same threshold. At a fixed luminosity, progressively redder galaxies are more strongly clustered on small scales, which can be explained by having a larger fraction of these galaxies in the form of satellites in massive halos. Our clustering measurements on scales below $0.4\,h^{-1}{\rm {Mpc}}$ allow us to study the small-scale spatial distribution of satellites inside halos. While the clustering of luminosity-threshold samples can be well described by a Navarro-Frenk-White (NFW) profile, that of the reddest galaxies prefers a steeper or more concentrated profile. Finally, we also use galaxy samples of constant number density at different redshifts to study the evolution of luminous galaxies, and find the clustering to be consistent with passive evolution in the redshift range of $0.5 \lesssim z \lesssim 0.6$.
    01/2014;
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    ABSTRACT: The puzzle of disk galaxy formation, and the formation of the Milky Way itself, remains unsolved. We analyze the present-day structure and assembly history of a high resolution hydrodynamic simulation of the formation of a Milky Way-like disk galaxy, from the ``Eris'' simulation suite, dissecting it into cohorts of stars formed at different epochs of cosmic history. The oldest disk cohorts form in structures that are radially compact and relatively thick, while subsequent cohorts form in progressively larger, thinner, colder configurations from gas with increasing levels of rotational support. The disk thus forms ``inside-out'' in a radial sense and ``upside-down'' in a vertical sense. While secular heating and radial migration may influence the final state of each age cohort, the dynamics of each co-eval population generically exhibit only minor evolution since formation. This assembly history is largely responsible for the galaxy's present-day correlations of stellar age with spatial and kinematic structure, which themselves are a good qualitative match to the observed correlations for mono-abundance stellar populations in the Milky Way.
    01/2014;
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    ABSTRACT: We present the cosmic distance scale as measured from the detection of the baryon acoustic oscillations (BAO) in the clustering of galaxies from the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). Our analysis of the Data Release 11 sample uses 1.15 million massive galaxies with spectroscopic redshifts spanning redshift 0.15 to 0.70 and covering 8500 square degrees. We find strong detections of the acoustic peak signature in two redshift bins centered at z=0.32 and z=0.57; in the upper redshift, the detection significance exceeds 8-sigma. These detections produce a robust measurement of the cosmic distance scale at these redshifts, including a 1% measurement of the distance to z=0.57. We discuss the cosmological implications of the measurements, including combinations with cosmic microwave background anisotropy data sets.
    01/2014;
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    ABSTRACT: Voids are the large, underdense regions in the cosmic web. While they are obviously useful cosmological probes, due to their intimate connection to the growth of structure, they are also interesting places to study astrophysics such as neutrino mass and primordial magnetic fields. I will present the latest work to identify voids in galaxy redshift surveys, how they connect to underdensities in dark matter, and the first results in exploiting their properties (sizes, shapes, interior contents) for scientific gain.
    01/2014;
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    ABSTRACT: I will present the first results mapping the 2-D distribution of circumgalactic gas around nearby dwarf galaxies from the COS-Dwarfs survey. COS-Dwarfs survey uses HST/COS spectroscopy to probe the halos of low redshift galaxies with luminosities L = (0.02 - 0.3)L*, stellar masses (M* ) = 10(8-10) Msun, up to impact parameters of 150 kpc. Using sensitive UV absorption-line measurements of the multiphase gas diagnostics such as Lyα, CII/IV, Si II/III/IV I will present the radial and azimuthal distribution of such gas around these galaxies. I will also show how the absorption strengths vary with host galaxy color, mass, star formation rate, orientation, and how they compare with that of the L* galaxies probed by our related COS-Halos survey. In particular, I will present the dependence of CIV absorption on specific star formation rate (sSFR) and a total mass estimate for carbon around these dwarf galaxies.
    01/2014;
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    Michael J. Mortonson, David H. Weinberg, Martin White
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    ABSTRACT: The accelerating expansion of the universe is the most surprising cosmological discovery in many decades. In this short review, we briefly summarize theories for the origin of cosmic acceleration and the observational methods being used to test these theories. We then discuss the current observational state of the field, with constraints from the cosmic microwave background (CMB), baryon acoustic oscillations (BAO), Type Ia supernovae (SN), direct measurements of the Hubble constant ($H_0$), and measurements of galaxy and matter clustering. Assuming a flat universe and dark energy with a constant equation-of-state parameter $w = P/\rho$, the combination of Planck CMB temperature anisotropies, WMAP CMB polarization, the Union2.1 SN compilation, and a compilation of BAO measurements yields $w = -1.10^{+0.08}_{-0.07}$, consistent with a cosmological constant ($w=-1$). However, with these constraints the cosmological constant model predicts a value of $H_0$ that is lower than several of the leading recent estimates, and it predicts a parameter combination $\sigma_8(\Omega_m)^{0.5}$ that is higher than many estimates from weak gravitational lensing, galaxy clusters, and redshift-space distortions. Individually these tensions are only significant at the ~$2\sigma$ level, but they arise in multiple data sets with independent statistics and distinct sources of systematic uncertainty. The tensions are stronger with Planck CMB data than they were with WMAP because of the smaller statistical errors and the higher central value of $\Omega_m.$ With the improved measurements expected from the next generation of data sets, these tensions may diminish, or they may sharpen in a way that points towards a more complete physical understanding of cosmic acceleration.
    12/2013;
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    ABSTRACT: How do observed voids relate to the underlying dark matter distribution? To examine the spatial distribution of dark matter contained within voids identified in galaxy surveys, we apply Halo Occupation Distribution models representing sparsely and densely sampled galaxy surveys to a high-resolution N-body simulation. We compare these galaxy voids to voids found in the halo distribution, low-resolution dark matter, and high-resolution dark matter. We find that voids at all scales in densely sampled surveys - and medium- to large-scale voids in sparse surveys - trace the same underdensities as dark matter, but they are larger in radius by ~20%, they have somewhat shallower density profiles, and they have centers offset by ~0.4Rv rms. However, in void-to-void comparison we find that shape estimators are less robust to sampling, and the largest voids in sparsely sampled surveys suffer fragmentation at their edges. We find that voids in galaxy surveys always correspond to underdensities in the dark matter, though the centers may be offset. When this offset is taken into account, we recover almost identical radial density profiles between galaxies and dark matter. All mock catalogs used in this work are available at http://www.cosmicvoids.net.
    11/2013; 438(4).
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    ABSTRACT: The Sloan Digital Sky Survey has surveyed 14,555 square degrees of the sky, and delivered over a trillion pixels of imaging data. We present the large-scale clustering of 1.6 million quasars between $z=0.5$ and $z=2.5$ that have been classified from this imaging, representing the highest density of quasars ever studied for clustering measurements. This data-set spans $\sim$ 11,000 square degrees and probes a volume of $80 h^{-3}$ Gpc$^3$ --- the largest volume ever probed by clustering measurements. In principle, such a large volume and high density of tracers should facilitate high-precision cosmological constraints. We measure the angular clustering of photometrically classified quasars using an optimal quadratic estimator in four redshift slices with an accuracy of $\sim 25\%$ over a bin width of $\delta_l \sim 10-15$ on scales corresponding to matter-radiation equality and larger ($\ell \sim 2-30$). Observational systematics can strongly bias clustering measurements on large scales, which can mimic cosmologically relevant signals such as deviations from Gaussianity in the spectrum of primordial perturbations. We account for systematics by employing a new method recently proposed by Agarwal et al. (2013) to the clustering of photometrically classified quasars. By carefully applying our methodology to mitigate known observational systematics, and removing angular bins that are contaminated by unknown systematics, we obtain constraints on local primordial non-Gaussianity of $f_{\rm NL} = 2^{+65}_{-66}$ (1$\sigma$ error) when we combine the quasar data with the photometric LRG sample of Ross et al. (2011) and Ho et al. (2012). The removal of unknown systematics is important since many angular scales of the quasar data are highly contaminated. [Abridged]
    11/2013;

Publication Stats

15k Citations
1,290.69 Total Impact Points

Institutions

  • 2014
    • University of Colorado
      Denver, Colorado, United States
  • 1970–2014
    • The Ohio State University
      • • Department of Astronomy
      • • Center for Cosmology and Astoparticle Physics
      Columbus, Ohio, United States
  • 2013
    • Vanderbilt University
      • Department of Physics and Astronomy
      Nashville, Michigan, United States
  • 2011–2013
    • Lawrence Berkeley National Laboratory
      • Physics Division
      Berkeley, California, United States
  • 2010–2013
    • Pennsylvania State University
      • Department of Astronomy and Astrophysics
      University Park, Maryland, United States
    • University of California, Santa Barbara
      • Department of Physics
      Santa Barbara, CA, United States
  • 2012
    • University of Utah
      • Department of Physics and Astronomy
      Salt Lake City, Utah, United States
    • Cea Leti
      Grenoble, Rhône-Alpes, France
    • University of Virginia
      • Department of Astronomy
      Charlottesville, Virginia, United States
  • 2009
    • Michigan State University
      • Center for the Study of Cosmic Evolution
      East Lansing, Michigan, United States
  • 2008
    • The University of Tokyo
      • Institute for Cosmic Ray Research
      Edo, Tōkyō, Japan
  • 2007
    • The University of Edinburgh
      • Institute for Astronomy (IfA)
      Edinburgh, Scotland, United Kingdom
    • Institut d'astrophysique de Paris
      Lutetia Parisorum, Île-de-France, France
  • 1990–2006
    • Princeton University
      • Department of Astrophysical Sciences
      Princeton, New Jersey, United States
  • 2002–2004
    • University of Chicago
      • Department of Astronomy and Astrophysics
      Chicago, Illinois, United States
    • Max Planck Institute for Astronomy
      Heidelburg, Baden-Württemberg, Germany
  • 2003
    • Max Planck Institute for Astrophysics
      Arching, Bavaria, Germany
  • 1998–2002
    • University of Massachusetts Amherst
      • Department of Astronomy
      Amherst Center, Massachusetts, United States
    • Harvard University
      • Department of Astronomy
      Cambridge, Massachusetts, United States
  • 2001
    • California Institute of Technology
      • Department of Astronomy
      Pasadena, California, United States
  • 1997
    • University of California, Santa Cruz
      • Department of Astronomy and Astrophysics
      Santa Cruz, California, United States
  • 1995
    • University of Washington Seattle
      • Department of Astronomy
      Seattle, Washington, United States
    • Durham University
      • Department of Physics
      Durham, ENG, United Kingdom
  • 1994
    • Institute for Advanced Study
      Princeton Junction, New Jersey, United States
  • 1992
    • University of California, Berkeley
      • Department of Astronomy
      Berkeley, CA, United States
  • 1991
    • Columbia University
      New York City, New York, United States