Robert C. Nichol

Publications (213)558.29 Total impact

• Article: Properties of type Ia supernovae inside rich galaxy clusters

  Henrique S. Xavier, Ravi R. Gupta, Masao Sako, Chris B. D'Andrea, Joshua A. Frieman, Lluis Galbany, Peter M. Garnavich, John Marriner, Robert C. Nichol, Matthew D. Olmstead, Donald P. Schneider, Mathew Smith
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  ABSTRACT: Using the GMBCG galaxy cluster catalogue and SDSS II supernovae data with redshifts measured by the BOSS project, we identified 48 SNe Ia residing in rich galaxy clusters (32 of which had useful host galaxy information) and analysed their properties. While most of their characteristics are consistent with other SNe Ia, their lightcurve stretch distribution is different from SNe Ia in the field. Although this result is consistent with a strong presence of passive host galaxies in our cluster sample, the consistency drops down for the inner parts of the cluster. We found evidences that the cluster environment might intensify the preference of SNe Ia in passive hosts for lower stretch. We also confirm previously known relations between SNe Ia and host properties and report that old passive galaxies host SNe Ia with lower stretch than young passive galaxies. We argue that this result is likely to be responsible for the lower stretch found for SNe Ia in rich clusters.
  04/2013;
• Article: Fitting Methods for Baryon Acoustic Oscillations in the Lyman-{\alpha} Forest Fluctuations in BOSS Data Release 9

  David Kirkby, Daniel Margala, Anže Slosar, Stephen Bailey, Nicolás G. Busca, Timothée Delubac, James Rich, Michael Blomqvist, Joel R. Brownstein, Bill Carithers, [......], Robert C. Nichol, Nathalie Palanque-Delabrouille, Isabelle Pâris, Patrick Petitjean, Graziano Rossi, David J. Schlegel, Donald P. Schneider, Matteo Viel, David H. Weinberg, Christophe Yèche
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  ABSTRACT: We describe fitting methods developed to analyze fluctuations in the Lyman-{\alpha} forest and measure the parameters of baryon acoustic oscillations (BAO). We apply our methods to BOSS Data Release 9. Our method is based on models of the three-dimensional correlation function in physical coordinate space, and includes the effects of redshift-space distortions, anisotropic non-linear broadening, and broadband distortions. We allow for independent scale factors along and perpendicular to the line of sight to minimize the dependence on our assumed fiducial cosmology and to obtain separate measurements of the BAO angular and relative velocity scales. Our fitting software and the input files needed to reproduce our main BOSS Data Release 9 results are publicly available.
  01/2013;
• Article: Measurement of Baryon Acoustic Oscillations in the Lyman-alpha Forest Fluctuations in BOSS Data Release 9

  Anže Slosar, Vid Iršič, David Kirkby, Stephen Bailey, Nicolás G. Busca, Timothée Delubac, James Rich, Vaishali Bhardwaj, Michael Blomqvist, Adam S. Bolton, [......], Yodovina Piškur N. A. Roe, Nicholas P. Ross, Graziano Rossi, David J. Schlegel, Donald P. Schneider, Erin S. Sheldon, Uroš Seljak, Matteo Viel, David H. Weinberg, Christophe Yèche
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  ABSTRACT: We use the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 9 (DR9) to detect and measure the position of the Baryonic Acoustic Oscillation (BAO) feature in the three-dimensional correlation function in the Lyman-alpha forest flux fluctuations at a redshift z=2.4. The feature is clearly detected at significance between 3 and 5 sigma (depending on the broadband model and method of error covariance matrix estimation) and is consistent with predictions of the standard LCDM model. We assess the biases in our method, stability of the error covariance matrix and possible systematic effects. We fit the resulting correlation function with several models that decouple the broadband and acoustic scale information. For an isotropic dilation factor, we measure 100x(alpha_iso-1) = -1.6 ^{+2.0+4.3+7.4}_{-2.0-4.1-6.8} (stat.) +/- 1.0 (syst.) (multiple statistical errors denote 1,2 and 3 sigma confidence limits) with respect to the acoustic scale in the fiducial cosmological model (flat LCDM with Omega_m=0.27, h=0.7). When fitting separately for the radial and transversal dilation factors we find marginalised constraints 100x(alpha_par-1) = -1.3 ^{+3.5+7.6 +12.3}_{-3.3-6.7-10.2} (stat.) +/- 2.0 (syst.) and 100x(alpha_perp-1) = -2.2 ^{+7.4+17}_{-7.1-15} +/- 3.0 (syst.). The dilation factor measurements are significantly correlated with cross-correlation coefficient of ~ -0.55. Errors become significantly non-Gaussian for deviations over 3 standard deviations from best fit value. Because of the data cuts and analysis method, these measurements give tighter constraints than a previous BAO analysis of the BOSS DR9 Lyman-alpha forest sample, providing an important consistency test of the standard cosmological model in a new redshift regime.
  01/2013;
• Article: SYNMAG Photometry: A Fast Tool for Catalog-Level Matched Colors of Extended Sources

  Kevin Bundy, David W. Hogg, Tim D. Higgs, Robert C. Nichol, Naoki Yasuda, Karen L. Masters, Dustin Lang, David A. Wake
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  ABSTRACT: Obtaining reliable, matched photometry for galaxies imaged by different observatories represents a key challenge in the era of wide-field surveys spanning more than several hundred square degrees. Methods such as flux fitting, profile fitting, and PSF homogenization followed by matched-aperture photometry are all computationally expensive. We present an alternative solution called "synthetic aperture photometry" that exploits galaxy profile fits in one band to efficiently model the observed, PSF-convolved light profile in other bands and predict the flux in arbitrarily sized apertures. Because aperture magnitudes are the most widely tabulated flux measurements in survey catalogs, producing synthetic aperture magnitudes (SYNMAGs) enables very fast matched photometry at the catalog level, without reprocessing imaging data. We make our code public and apply it to obtain matched photometry between SDSS ugriz and UKIDSS YJHK imaging, recovering red-sequence colors and photometric redshifts with a scatter and accuracy as good as if not better than FWHM-homogenized photometry from the GAMA Survey. Finally, we list some specific measurements that upcoming surveys could make available to facilitate and ease the use of SYNMAGs.
  01/2013;
• Article: The Fundamental Metallicity Relation Reduces Type Ia SN Hubble Residuals More Than Host Mass Alone

  Brian T. Hayden, Ravi R. Gupta, Peter M. Garnavich, Filippo Mannucci, Robert C. Nichol, Masao Sako
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  ABSTRACT: Type Ia Supernova Hubble residuals have been shown to correlate with host galaxy mass, imposing a major obstacle for their use in measuring dark energy properties. Here, we calibrate the fundamental metallicity relation (FMR) of Mannucci et al. (2010) for host mass and star formation rates measured from broad-band colors alone. We apply the FMR to the large number of hosts from the SDSS-II sample of Gupta et al. (2011) and find that the scatter in the Hubble residuals is significantly reduced when compared with using only stellar mass (or the mass-metallicity relation) as a fit parameter. Our calibration of the FMR is restricted to only star-forming galaxies and in the Hubble residual calculation we include only hosts with log(SFR) > -2. Our results strongly suggest that metallicity is the underlying source of the correlation between Hubble residuals and host galaxy mass. Since the FMR is nearly constant between z = 2 and the present, use of the FMR along with light curve width and color should provide a robust distance measurement method that minimizes systematic errors.
  12/2012;
• Article: MegaMorph - multi-wavelength measurement of galaxy structure: complete S\'ersic profile information from modern surveys

  Boris Häußler, Steven P. Bamford, Marina Vika, Alex L. Rojas, Marco Barden, Lee S. Kelvin, Mehmet Alpaslan, Aaron S. G. Robotham, Simon P. Driver, I. K. Baldry, Sarah Brough, Andrew M. Hopkins, Jochen Liske, Robert C. Nichol, Cristina. C. Popescu, Richard J. Tuffs
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  ABSTRACT: In this paper, we demonstrate a new method for fitting galaxy profiles which makes use of the full multi-wavelength data provided by modern large optical-near-infrared imaging surveys. We present a new version of GALAPAGOS, which utilises a recently-developed multi-wavelength version of GALFIT, and enables the automated measurement of wavelength dependent S\'ersic profile parameters for very large samples of galaxies. Our new technique is extensively tested to assess the reliability of both pieces of software, GALFIT and GALAPAGOS on both real ugrizY JHK imaging data from the GAMA survey and simulated data made to the same specifications. We find that fitting galaxy light profiles with multi-wavelength data increases the stability and accuracy of the measured parameters, and hence produces more complete and meaningful multi-wavelength photometry than has been available previously. The improvement is particularly significant for magnitudes in low S/N bands and for structural parameters like half-light radius re and S\'ersic index n for which a prior is used by constraining these parameters to a polynomial as a function of wavelength. This allows the fitting routines to push the magnitude of galaxies for which sensible values can be derived to fainter limits. The technique utilises a smooth transition of galaxy parameters with wavelength, creating more physically meaningful transitions than single-band fitting and allows accurate interpolation between passbands, perfect for derivation of rest-frame values.
  12/2012;
• Article: Cosmology with Photometrically-Classified Type Ia Supernovae from the SDSS-II Supernova Survey

  Heather Campbell, Chris B. D'Andrea, Robert C. Nichol, Masao Sako, Mathew Smith, Hubert Lampeitl, Matthew D. Olmstead, Bruce Bassett, Rahul Biswas, Peter Brown, [......], Steve Kuhlmann, Martin Kunz, John Marriner, Ramon Miquel, Michael Richmond, Adam Riess, Donald P. Schneider, Jesper Sollerman, Matt Taylor, Gong-Bo Zhao
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  ABSTRACT: We present the cosmological analysis of 752 photometrically-classified Type Ia Supernovae (SNe Ia) obtained from the full Sloan Digital Sky Survey II (SDSS-II) Supernova (SN) Survey, supplemented with host-galaxy spectroscopy from the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). Our photometric-classification method is based on the SN typing technique of Sako et al. (2011), aided by host galaxy redshifts (0.05<z<0.55). SNANA simulations of our methodology estimate that we have a SN Ia typing efficiency of 70.8%, with only 3.9% contamination from core-collapse (non-Ia) SNe. We demonstrate that this level of contamination has no effect on our cosmological constraints. We quantify and correct for our selection effects (e.g., Malmquist bias) using simulations. When fitting to a flat LambdaCDM cosmological model, we find that our photometric sample alone gives omega_m=0.24+0.07-0.05 (statistical errors only). If we relax the constraint on flatness, then our sample provides competitive joint statistical constraints on omega_m and omega_lambda, comparable to those derived from the spectroscopically-confirmed three-year Supernova Legacy Survey (SNLS3). Using only our data, the statistics-only result favors an accelerating universe at 99.96% confidence. Assuming a constant wCDM cosmological model, and combining with H0, CMB and LRG data, we obtain w=-0.96+0.10-0.10, omega_m=0.29+0.02-0.02 and omega_k=0.00+0.03-0.02 (statistical errors only), which is competitive with similar spectroscopically confirmed SNe Ia analyses. Overall this comparison is re-assuring, considering the lower redshift leverage of the SDSS-II SN sample (z<0.55) and the lack of spectroscopic confirmation used herein. These results demonstrate the potential of photometrically-classified SNe Ia samples in improving cosmological constraints.
  11/2012;
• Article: The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: the low redshift sample

  John K. Parejko, Tomomi Sunayama, Nikhil Padmanabhan, David A. Wake, Andreas A. Berlind, Dmitry Bizyaev, Michael Blanton, Adam S. Bolton, Frank van den Bosch, Jon Brinkmann, [......], Ramin Skibba, Jeremy Tinker, Rita Tojeiro, Benjamin A. Weaver, Andrew Wetzel, Martin White, David H. Weinberg, Daniel Thomas, Idit Zehavi, Zheng Zheng
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  ABSTRACT: We report on the small scale (0.5<r<40h^-1 Mpc) clustering of 78895 massive (M*~10^11.3M_sun) galaxies at 0.2<z<0.4 from the first two years of data from the Baryon Oscillation Spectroscopic Survey (BOSS), to be released as part of SDSS Data Release 9 (DR9). We describe the sample selection, basic properties of the galaxies, and caveats for working with the data. We calculate the real- and redshift-space two-point correlation functions of these galaxies, fit these measurements using Halo Occupation Distribution (HOD) modeling within dark matter cosmological simulations, and estimate the errors using mock catalogs. These galaxies lie in massive halos, with a mean halo mass of 5.2x10^13 h^-1 M_sun, a large scale bias of ~2.0, and a satellite fraction of 12+/-2%. Thus, these galaxies occupy halos with average masses in between those of the higher redshift BOSS CMASS sample and the original SDSS I/II LRG sample.
  11/2012;
• Article: Baryon Acoustic Oscillations in the Ly-\alpha\ forest of BOSS quasars

  Nicolás G. Busca, Timothée Delubac, James Rich, Stephen Bailey, Andreu Font-Ribera, David Kirkby, J. -M. Le Goff, Matthew M. Pieri, Anze Slosar, Éric Aubourg, [......], Erin S. Sheldon, Audrey Simmons, Stephanie Snedden, Jeremy L. Tinker, Matteo Viel, Benjamin A. Weaver, David H. Weinberg, Martin White, Christophe Yèche, Donald G. York
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  ABSTRACT: We report a detection of the baryon acoustic oscillation (BAO) feature in the three-dimensional correlation function of the transmitted flux fraction in the \Lya forest of high-redshift quasars. The study uses 48,640 quasars in the redshift range $2.1\le z \le 3.5$ from the Baryon Oscillation Spectroscopic Survey (BOSS) of the third generation of the Sloan Digital Sky Survey (SDSS-III). At a mean redshift $z=2.3$, we measure the monopole and quadrupole components of the correlation function for separations in the range $20\hMpc<r<200\hMpc$. A peak in the correlation function is seen at a separation equal to $(1.01\pm0.03)$ times the distance expected for the BAO peak within a concordance $\Lambda$CDM cosmology. This first detection of the BAO peak at high redshift, when the universe was strongly matter dominated, results in constraints on the angular diameter distance $\da$ and the expansion rate $H$ at $z=2.3$ that, combined with priors on $H_0$ and the baryon density, require the existence of dark energy. Combined with constraints derived from Cosmic Microwave Background (CMB) observations, this result implies $H(z=2.3)=(224\pm8){\rm km\,s^{-1}Mpc^{-1}}$, indicating that the time derivative of the cosmological scale parameter $\dot{a}=H(z=2.3)/(1+z)$ is significantly greater than that measured with BAO at $z\sim0.5$. This demonstrates that the expansion was decelerating in the range $0.7<z<2.3$, as expected from the matter domination during this epoch. Combined with measurements of $H_0$, one sees the pattern of deceleration followed by acceleration characteristic of a dark-energy dominated universe.
  11/2012;
• Article: SNe Ia host galaxy properties from Sloan Digital Sky Survey-II spectroscopy

  Jonas Johansson, Daniel Thomas, Janine Pforr, Claudia Maraston, Robert C. Nichol, Mathew Smith, Hubert Lampeitl, Alessandra Beifiori, Ravi R. Gupta, Donald P. Schneider
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  ABSTRACT: We study the stellar populations of SNe Ia host galaxies using SDSS-II spectroscopy. We focus on the relationships of SNe Ia properties with stellar velocity dispersion and the stellar population parameters age, metallicity and element abundance ratios derived by fitting absorption line indices to stellar population models. We concentrate on a sub-sample of 84 SNe Ia from the SDSS-II Supernova Survey. In agreement with previous findings, we find that SALT2 stretch factor values show the strongest dependence on stellar population age. Hence, SNe Ia peak-luminosity is closely related to the age of the stellar progenitor systems, where more luminous SNe Ia appear in younger stellar populations. We find no statistically significant trends in the Hubble residual with any of the stellar population parameters studied, including age and metallicity contrary to the literature, as well as with stellar velocity dispersion. Moreover, we find that the method of stellar mass derivation is affecting the Hubble residual-mass relationship when lower number statistics are used. We extend the sample to also include SNe Ia with available SDSS host galaxy photometry only. For this larger sample (247 objects) the reported Hubble residual-mass relation is strongly dependent on the stellar mass range studied and behaves as a step function. In the high mass regime, probed by our host spectroscopy sample, the relation between Hubble residual and stellar mass is flat. Below a stellar mass of ~2x10^10 Msun, i.e. close to the evolutionary transition mass of low-redshift galaxies reported in the literature, the trend changes dramatically such that lower mass galaxies possess lower luminosity SNe Ia after light-curve corrections. This non-linear behaviour of the Hubble residual-mass relationship should be accounted for when using stellar mass as a further parameter for minimising the Hubble residuals.
  11/2012;
• Article: Reconstructing gravity beyond the local universe with peculiar velocities

  Russell Johnston, David Bacon, Luis F. A. Teodoro, Robert C. Nichol, Michael S. Warren, Catherine Cress
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  ABSTRACT: We study a maximum probability approach to reconstructing spatial maps of the Newtonian gravitational potential, \Psi, from peculiar velocities of galaxies at redshifts beyond z~0.1, where peculiar velocities have been measured from distance indicators (DI) such as the Tully-Fisher relation. With the large statistical uncertainties associated with DIs (of the order ~20% in distance), our reconstruction method aims to recover the underlying true peculiar velocity field with sufficient precision to be used as a cosmological probe of gravity, by reducing these statistical errors with the use of two physically motivated filtering prior terms. The first constructs an estimate of the velocity field derived from the galaxy over-density, \delta_g, and the second makes use of the matter linear density power spectrum P(k). Through the use of N-body simulations we demonstrate that, with measurements with a suitably high signal-to-noise, we can successfully reconstruct the velocity and gravitational potential field out to z~0.3. This will prove useful for future tests of gravity, as these relatively deep maps are complementary to weak lensing maps at the same redshift.
  10/2012;
• Article: The Multi-Object, Fiber-Fed Spectrographs for SDSS and the Baryon Oscillation Spectroscopic Survey

  Stephen Smee, James E. Gunn, Alan Uomoto, Natalie Roe, David Schlegel, Constance M. Rockosi, Michael A. Carr, French Leger, Kyle S. Dawson, Matthew D. Olmstead, [......], Walter Siegmund, Audrey Simmons, D. Smith, Stephanie Snedden, Donald P. Schneider, Michael Strauss, Mark SubbaRao, Christy Tremonti, Patrick Waddell, Donald G. York
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  ABSTRACT: We present the design and performance of the multi-object fiber spectrographs for the Sloan Digital Sky Survey (SDSS) and their upgrade for the Baryon Oscillation Spectroscopic Survey (BOSS). Originally commissioned in Fall 1999 on the 2.5-m aperture Sloan Telescope at Apache Point Observatory, the spectrographs produced more than 1.5 million spectra for the SDSS and SDSS-II surveys, enabling a wide variety of Galactic and extra-galactic science including the first observation of baryon acoustic oscillations in 2005. The spectrographs were upgraded in 2009 and are currently in use for BOSS, the flagship survey of the third-generation SDSS-III project. BOSS will measure redshifts of 1.35 million massive galaxies to redshift 0.7 and Lyman-$\alpha$ absorption of 160,000 high redshift quasars over 10,000 square degrees of sky, making percent level measurements of the absolute cosmic distance scale of the Universe and placing tight constraints on the equation of state of dark energy. The twin multi-object fiber spectrographs utilize a simple optical layout with reflective collimators, all-refractive cameras, gratings, and state-of-the-art CCD detectors to produce hundreds of spectra simultaneously in two channels over a bandpass covering the near ultraviolet to the near infrared, with a resolving power R = \lambda/FWHM ~ 2000. Building on proven heritage, the spectrographs were upgraded for BOSS with volume-phase holographic gratings and modern CCD detectors, improving the peak throughput by nearly a factor of two, extending the bandpass to cover 360 < \lambda < 1000 nm, and increasing the number of fibers from 640 to 1000 per exposure. In this paper we describe the original SDSS spectrograph design and the upgrades implemented for BOSS, and document the predicted and measured performances.
  08/2012;
• Article: The Clustering of Galaxies in SDSS-III DR9 Baryon OscillationSpectroscopic Survey: Constraints on Primordial Non-Gaussianity

  Ashley J. Ross, Will J. Percival, Aurelio Carnero, Gong-bo Zhao, Marc Manera, Alvise Raccanelli, Eric Aubourg, Dmitry Bizyaev, Howard Brewington, J. Brinkmann, [......], Donald P. Schneider, Hee-Jong Seo, Alaina Sheldon, Audrey Simmons, Stephanie Snedden, Molly E. C. Swanson, Daniel Thomas, Jeremy L. Tinker, Rita Tojeiro, Idit Zehavi
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  ABSTRACT: We analyze the density field of 264,283 galaxies observed by the Sloan Digital Sky Survey (SDSS)-III Baryon Oscillation Spectroscopic Survey (BOSS) and included in the SDSS data release nine (DR9). In total, the SDSS DR9 BOSS data includes spectroscopic redshifts for over 400,000 galaxies spread over a footprint of more than 3,000 deg^2. We measure the power spectrum of these galaxies with redshifts 0.43 < z < 0.7 in order to constrain the amount of local non-Gaussianity, f_NL,local, in the primordial density field, paying particular attention to the impact of systematic uncertainties. The BOSS galaxy density field is systematically affected by the local stellar density and this influences the ability to accurately measure f_NL,local. In the absence of any correction, we find (erroneously) that the probability that f_NL,local is greater than zero, P(f_NL,local >0), is 99.5%. After quantifying and correcting for the systematic bias and including the added uncertainty, we find -45 < f_NL,local < 195 at 95% confidence, and P(f_NL,local >0) = 91.0%. A more conservative approach assumes that we have only learned the k-dependence of the systematic bias and allows any amplitude for the systematic correction; we find that the systematic effect is not fully degenerate with that of f_NL,local, and we determine that -82 < f_NL,local < 178 (at 95% confidence) and P(f_NL,local >0) = 68%. This analysis demonstrates the importance of accounting for the impact of Galactic foregrounds on f_NL,local measurements. We outline the methods that account for these systematic biases and uncertainties. We expect our methods to yield robust constraints on f_NL,local for both our own and future large-scale-structure investigations.
  Monthly Notices of the Royal Astronomical Society 08/2012; 428(2). · 4.90 Impact Factor
• Source

  Available from: Sebastian E. Nuza

  Article: The Baryon Oscillation Spectroscopic Survey of SDSS-III

  Kyle S. Dawson, David J. Schlegel, Christopher P. Ahn, Scott F. Anderson, Éric Aubourg, Stephen Bailey, Robert H. Barkhouser, Julian E. Bautista, Alessandra Beifiori, Andreas A. Berlind, [......], Benjamin A. Weaver, David H. Weinberg, Benjamin J. Weiner, Andrew A. West, Martin White, W. M. Wood-Vasey, Christophe Yeche, Idit Zehavi, Gong-Bo Zhao, Zheng Zheng
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  ABSTRACT: The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the scale of baryon acoustic oscillations (BAO) in the clustering of matter over a larger volume than the combined efforts of all previous spectroscopic surveys of large scale structure. BOSS uses 1.5 million luminous galaxies as faint as i=19.9 over 10,000 square degrees to measure BAO to redshifts z<0.7. Observations of neutral hydrogen in the Lyman alpha forest in more than 150,000 quasar spectra (g<22) will constrain BAO over the redshift range 2.15<z<3.5. Early results from BOSS include the first detection of the large-scale three-dimensional clustering of the Lyman alpha forest and a strong detection from the Data Release 9 data set of the BAO in the clustering of massive galaxies at an effective redshift z = 0.57. We project that BOSS will yield measurements of the angular diameter distance D_A to an accuracy of 1.0% at redshifts z=0.3 and z=0.57 and measurements of H(z) to 1.8% and 1.7% at the same redshifts. Forecasts for Lyman alpha forest constraints predict a measurement of an overall dilation factor that scales the highly degenerate D_A(z) and H^{-1}(z) parameters to an accuracy of 1.9% at z~2.5 when the survey is complete. Here, we provide an overview of the selection of spectroscopic targets, planning of observations, and analysis of data and data quality of BOSS.
  07/2012;
• Article: The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey

  SDSS-III Collaboration: Christopher P. Ahn, Rachael Alexandroff, Carlos Allende Prieto, Scott F. Anderson, Timothy Anderton, Brett H. Andrews, Éric Aubourg Stephen Bailey, Rory Barnes, Julian Bautista, Timothy C. Beers, [......], Brian Yanny, Christophe Yèche, Donald G. York, O. Zamora, Gail Zasowski, Idit Zehavi, Gong-Bo Zhao, Zheng Zheng, Guangtun Zhu, Joel C. Zinn
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  ABSTRACT: The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar spectra, along with the data presented in previous data releases. These spectra were obtained with the new BOSS spectrograph and were taken between 2009 December and 2011 July. In addition, the stellar parameters pipeline, which determines radial velocities, surface temperatures, surface gravities, and metallicities of stars, has been updated and refined with improvements in temperature estimates for stars with T_eff<5000 K and in metallicity estimates for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars presented in DR8, including stars from SDSS-I and II, as well as those observed as part of the SDSS-III Sloan Extension for Galactic Understanding and Exploration-2 (SEGUE-2). The astrometry error introduced in the DR8 imaging catalogs has been corrected in the DR9 data products. The next data release for SDSS-III will be in Summer 2013, which will present the first data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) along with another year of data from BOSS, followed by the final SDSS-III data release in December 2014.
  07/2012;
• Article: The clustering of galaxies in the SDSS-III Baryon OscillationSpectroscopic Survey: Analysis of potential systematics

  Ashley J. Ross, Will J. Percival, Ariel G. Sanchez, Lado Samushia, Shirley Ho, Eyal Kazin, Marc Manera, Beth Reid, Martin White, Rita Tojeiro, [......], Antonio J. Cuesta, Elena Malanushenko, Viktor Malanushenko, Daniel Oravetz, John Parejko, Kaike Pan, Donald P. Schneider Alaina Shelden, Audrey Simmons, Stephanie Snedden, Gong-bo Zhao
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  ABSTRACT: We analyze the density field of galaxies observed by the Sloan Digital Sky Survey (SDSS)-III Baryon Oscillation Spectroscopic Survey (BOSS) included in the SDSS Data Release Nine (DR9). DR9 includes spectroscopic redshifts for over 400,000 galaxies spread over a footprint of 3,275 deg^2. We identify, characterize, and mitigate the impact of sources of systematic uncertainty on large-scale clustering measurements, both for angular moments of the redshift-space correlation function and the spherically averaged power spectrum, P(k), in order to ensure that robust cosmological constraints will be obtained from these data. A correlation between the projected density of stars and the higher redshift (0.43 < z < 0.7) galaxy sample (the `CMASS' sample) due to imaging systematics imparts a systematic error that is larger than the statistical error of the clustering measurements at scales s > 120h^-1Mpc or k < 0.01hMpc^-1. We find that these errors can be ameliorated by weighting galaxies based on their surface brightness and the local stellar density. We use mock galaxy catalogs that simulate the CMASS selection function to determine that randomly selecting galaxy redshifts in order to simulate the radial selection function of a random sample imparts the least systematic error on correlation function measurements and that this systematic error is negligible for the spherically averaged correlation function. The methods we recommend for the calculation of clustering measurements using the CMASS sample are adopted in companion papers that locate the position of the baryon acoustic oscillation feature (Anderson et al. 2012), constrain cosmological models using the full shape of the correlation function (Sanchez et al. 2012), and measure the rate of structure growth (Reid et al. 2012). (abridged)
  Monthly Notices of the Royal Astronomical Society 07/2012; 424(1). · 4.90 Impact Factor
• Article: Stellar masses of SDSS-III BOSS galaxies at z~0.5 and constraints to galaxy formation models

  Claudia Maraston, Janine Pforr, Bruno M. Henriques, Daniel Thomas, David Wake, Joel R. Brownstein, Diego Capozzi, Kevin Bundy, Ramin A. Skibba, Alessandra Beifiori, [......], Donald G. York, Dmitry Bizyaev, Howard Brewington, Elena Malanushenko, Viktor Malanushenko, Stephanie Snedden, Daniel Oravetz, Kaike Pan, Alaina Shelden, Audrey Simmons
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  ABSTRACT: We calculate stellar masses for ~400,000 massive luminous galaxies at redshift ~0.2-0.7 using the first two years of data from the Baryon Oscillation Spectroscopic Survey (BOSS). Stellar masses are obtained by fitting model spectral energy distributions to u,g,r,i,z magnitudes. Accurate BOSS spectroscopic redshifts are used to constrain the fits. We find that the distribution of stellar masses in BOSS is narrow (Delta log M ~0.5 dex) and peaks at about log M/M_sun ~ 11.3 (for a Kroupa initial stellar mass function), and that the mass sampling is uniform over the redshift range 0.2 to 0.6, in agreement with the intended BOSS target selection. The galaxy masses probed by BOSS extend over ~ 10^{12} M_{sun}, providing unprecedented measurements of the high-mass end of the galaxy mass function. We find that the galaxy number density above ~ 2.5 10^{11} M_{sun} agrees with previous determinations within 2sigma, but there is a slight offset towards lower number densities in BOSS. This alleviates a tension between the z < 0.1 and the high-redshift mass function. We perform a comparison with semi-analytic galaxy formation models tailored to the BOSS target selection and volume, in order to contain incompleteness. The abundance of massive galaxies in the models compare well with the BOSS data. However, no evolution is detected from redshift ~ 0.6 to 0 in the data, whereas the abundance of massive galaxies in the models increases to redshift zero. BOSS data display colour-magnitude (mass) relations similar to those found in the local Universe, where the most massive galaxies are the reddest. On the other hand, the model colours do not display a dependence on stellar mass, span a narrower range and are typically bluer than the observations. We argue that the lack of a colour-mass relation in the models is mostly due to metallicity, which is too low in the models.
  07/2012;
• Article: The Clustering of Galaxies in the SDSS-III DR9 Baryon Oscillation Spectroscopic Survey: Testing Deviations from $\Lambda$ and General Relativity using anisotropic clustering of galaxies

  Lado Samushia, Beth A. Reid, Martin White, Will J. Percival, Antonio J. Cuesta, Lucas Lombriser, Marc Manera, Robert C. Nichol, Donald P. Schneider, Dmitry Bizyaev, [......], Viktor Malanushenko, Daniel Oravetz, Kaike Pan, Audrey Simmons, Alaina Shelden, Stephanie Snedden, Jeremy L. Tinker, Benjamin A. Weaver, Donald G. York, Gong-Bo Zhao
  [show abstract] [hide abstract]
  ABSTRACT: We use the joint measurement of geometry and growth from anisotropic galaxy clustering in the Baryon Oscillation Spectroscopic Survey Data Release 9 CMASS sample reported by Reid et al. to constrain dark energy properties and possible deviations from the General Relativity. Assuming GR and taking a prior on the linear matter power spectrum at high redshift from the cosmic microwave background (CMB), anisotropic clustering of the CMASS DR9 galaxies alone constrains $\Omega_{\rm m} = 0.308 \pm 0.022$ and $100\Omega_{\rm k} = 5.9 \pm 4.8$ for $w = -1$, or $w = -0.91 \pm 0.12$ for $\Omega_k = 0$. When combined with the full CMB likelihood, the addition of the anisotropic clustering measurements to the spherically-averaged BAO location increases the constraining power on dark energy by a factor of 4 in a flat CDM cosmology with constant dark energy equation of state $w$ (giving $w = -0.87 \pm 0.05$). This impressive gain depends on our measurement of both the growth of structure and Alcock-Paczynski effect, and is not realised when marginalising over the amplitude of redshift space distortions. Combining with both the CMB and Supernovae Type Ia (SNeIa), we find $\Omega_{\rm m} = 0.281 \pm 0.014$ and $1000\Omega_{\rm k}=-9.2\pm5.0$ for $w = -1$, or $w_0 = -1.13 \pm 0.12$ and $w_{\rm a}=0.65 \pm 0.36$ assuming $\Omega_k = 0$. Finally, when a $\Lambda$CDM background expansion is assumed, the combination of our estimate of the growth rate with previous growth measurements provides tight constraints on the parameters describing possible deviations from GR giving $\gamma = 0.64 \pm 0.05$. For one parameter extensions of the flat $\Lambda$CDM model, we find a $\sim 2\sigma$ preference either for $w > -1$ or slower growth than in GR. However, the data is fully consistent with the concordance model, and the evidence for these additional parameters is weaker than $2\sigma$.
  06/2012;
• Article: Galaxy Zoo: Quantifying Morphological Indicators of Galaxy Interaction

  Kevin R. V. Casteels, Steven P. Bamford, Ramin A. Skibba, Karen L. Masters, Chris J. Lintott, William C. Keel, Kevin Schawinski, Robert C. Nichol, Arfon M. Smith
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  ABSTRACT: We use Galaxy Zoo 2 visual classifications to study the morphological signatures of interaction between similar-mass galaxy pairs in the Sloan Digital Sky Survey. We find that many observable features correlate with projected pair separation; not only obvious indicators of merging, disturbance and tidal tails, but also more regular features, such as spiral arms and bars. These trends are robustly quantified, using a control sample to account for observational biases, producing measurements of the strength and separation scale of various morphological responses to pair interaction. For example, we find that the presence of spiral features is enhanced at scales < 70 h^-1 kpc, probably due to both increased star formation and the formation of tidal tails. On the other hand, the likelihood of identifying a bar decreases significantly in pairs with separations < 30 h^-1 kpc, suggesting that bars are suppressed by close interactions between galaxies of similar mass. We go on to show how morphological indicators of physical interactions provide a way of significantly refining standard estimates for the frequency of close pair interactions, based on velocity offset and projected separation. The presence of loosely wound spiral arms is found to be a particularly reliable signal of an interaction, for projected pair separations up to ~100 h^-1 kpc. We use this indicator to demonstrate our method, constraining the fraction of low-redshift galaxies in truly interacting pairs, with M_* > 10^9.5 M_Sun and mass ratio < 4, to be between 0.4 - 2.7 per cent.
  06/2012;
• Source

  Available from: Lluís Galbany

  Article: Type Ia Supernova Properties as a Function of the Distance to the Host Galaxy in the SDSS-II SN Survey

  Lluis Galbany, Ramon Miquel, Linda Ostman, Peter J. Brown, David Cinabro, Chris B. D'Andrea, Joshua Frieman, Saurabh W. Jha, John Marriner, Robert C. Nichol, [......], Jesper Sollerman, Kaike Pan, Stephanie Snedden, Dmitry Bizyaev, Howard Brewington, Elena Malanushenko, Viktor Malanushenko, Dan Oravetz, Audrey Simmons, Alaina Shelden
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  ABSTRACT: We use type-Ia supernovae (SNe Ia) discovered by the SDSS-II SN Survey to search for dependencies between SN Ia properties and the projected distance to the host galaxy center, using the distance as a proxy for local galaxy properties (local star-formation rate, local metallicity, etc.). The sample consists of almost 200 spectroscopically or photometrically confirmed SNe Ia at redshifts below 0.25. The sample is split into two groups depending on the morphology of the host galaxy. We fit light-curves using both MLCS2k2 and SALT2, and determine color (AV, c) and light-curve shape (delta, x1) parameters for each SN Ia, as well as its residual in the Hubble diagram. We then correlate these parameters with both the physical and the normalized distances to the center of the host galaxy and look for trends in the mean values and scatters of these parameters with increasing distance. The most significant (at the 4-sigma level) finding is that the average fitted AV from MLCS2k2 and c from SALT2 decrease with the projected distance for SNe Ia in spiral galaxies. We also find indications that SNe in elliptical galaxies tend to have narrower light-curves if they explode at larger distances, although this may be due to selection effects in our sample. We do not find strong correlations between the residuals of the distance moduli with respect to the Hubble flow and the galactocentric distances, which indicates a limited correlation between SN magnitudes after standardization and local host metallicity.
  06/2012;