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The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: galaxy clustering measurements in the low redshift sample of Data Release 11

Rita Tojeiro, Ashley J. Ross, Angela Burden, Lado Samushia, Marc Manera, Will J. Percival, Florian Beutler, Antonio J. Cuesta, Kyle Dawson, Daniel J. Eisenstein, Shirley Ho, Cullan Howett, Cameron K. McBride, Francisco Montesano, John K. Parejko, Beth Reid, Ariel G. Sánchez, David J. Schlegel, Donald P. Schneider, Jeremy L. Tinker, Mariana Vargas Magaña, Martin White

TL;DR

This study delivers the first robust large-scale clustering measurements for SDSS-III BOSS DR11 LOWZ at a mean redshift of $\langle z\rangle\approx0.32$, using 313,780 galaxies across 7,341 deg$^2$. By reconstructing the density field and analyzing both the power spectrum $P(k)$ and correlation function $\xi(s)$, the authors extract an isotropic BAO dilation parameter $\alpha = 1.018\pm0.020$, corresponding to a distance measure $D_V(z)$ with tight constraints when combined with DR11 DR11-LOWZ and DR12 CMASS results. Thorough systematic tests show the sample is robust to photometric offsets and observational systematics, with north-south tensions attributable to calibration or sample variance and not to the BAO signal itself. Reconstruction yields substantial improvements in BAO precision (up to ~85% in $\xi(s)$ and ~59% in $P(k)$), and the DR11 LOWZ results are consistent with DR10 while providing the most precise intermediate-redshift distance constraint when paired with CMASS, enhancing cosmological parameter constraints. The work demonstrates the reliability of LOWZ BAO measurements and their value for constraining the expansion history of the Universe.

Abstract

We present the distance measurement to z = 0.32 using the 11th data release of the Sloan Digital Sky Survey-III Baryon Acoustic Oscillation Survey (BOSS). We use 313,780 galaxies of the low-redshift (LOWZ) sample over 7,341 square-degrees to compute $D_V = (1264 \pm 25)(r_d/r_{d,fid})$ - a sub 2% measurement - using the baryon acoustic feature measured in the galaxy two-point correlation function and power-spectrum. We compare our results to those obtained in DR10. We study observational systematics in the LOWZ sample and quantify potential effects due to photometric offsets between the northern and southern Galactic caps. We find the sample to be robust to all systematic effects found to impact on the targeting of higher-redshift BOSS galaxies, and that the observed north-south tensions can be explained by either limitations in photometric calibration or by sample variance, and have no impact on our final result. Our measurement, combined with the baryonic acoustic scale at z = 0.57, is used in Anderson et al. (2013a) to constrain cosmological parameters.

The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: galaxy clustering measurements in the low redshift sample of Data Release 11

TL;DR

This study delivers the first robust large-scale clustering measurements for SDSS-III BOSS DR11 LOWZ at a mean redshift of , using 313,780 galaxies across 7,341 deg. By reconstructing the density field and analyzing both the power spectrum and correlation function , the authors extract an isotropic BAO dilation parameter , corresponding to a distance measure with tight constraints when combined with DR11 DR11-LOWZ and DR12 CMASS results. Thorough systematic tests show the sample is robust to photometric offsets and observational systematics, with north-south tensions attributable to calibration or sample variance and not to the BAO signal itself. Reconstruction yields substantial improvements in BAO precision (up to ~85% in and ~59% in ), and the DR11 LOWZ results are consistent with DR10 while providing the most precise intermediate-redshift distance constraint when paired with CMASS, enhancing cosmological parameter constraints. The work demonstrates the reliability of LOWZ BAO measurements and their value for constraining the expansion history of the Universe.

Abstract

We present the distance measurement to z = 0.32 using the 11th data release of the Sloan Digital Sky Survey-III Baryon Acoustic Oscillation Survey (BOSS). We use 313,780 galaxies of the low-redshift (LOWZ) sample over 7,341 square-degrees to compute - a sub 2% measurement - using the baryon acoustic feature measured in the galaxy two-point correlation function and power-spectrum. We compare our results to those obtained in DR10. We study observational systematics in the LOWZ sample and quantify potential effects due to photometric offsets between the northern and southern Galactic caps. We find the sample to be robust to all systematic effects found to impact on the targeting of higher-redshift BOSS galaxies, and that the observed north-south tensions can be explained by either limitations in photometric calibration or by sample variance, and have no impact on our final result. Our measurement, combined with the baryonic acoustic scale at z = 0.57, is used in Anderson et al. (2013a) to constrain cosmological parameters.

Paper Structure

This paper contains 27 sections, 19 equations, 12 figures, 5 tables.

Table of Contents

  1. Introduction
  2. Data
  3. Target selection
  4. Galaxy catalogues
  5. Random catalogues
  6. Checking for systematic effects
  7. Observational effects on targets
  8. Photometric offsets
  9. Number density
  10. Colours
  11. Clustering
  12. Fluctuations with Right Ascension
  13. Analysis
  14. Reconstruction
  15. Power-spectrum
  16. ...and 12 more sections

Figures (12)

  • Figure 1: The expected number density of BOSS and SDSS-II LRG targets as a function of redshift. The number densities shown here are corrected for missing targets due to close pairs, redshift failures and completeness - see Table \ref{['tab:sample_summary']} for details.
  • Figure 2: Survey footprint in equatorial coordinates. DR10 on the two left panels and DR11 on the two right panels (North and South galactic caps in the top and bottom panels, respectively). The color code shows the completeness of each sector.
  • Figure 3: Bottom panel: Fluctuations of on-sky angular target density in the NGC as a function of angular stellar density. The coloured symbols show this relationship for LOWZ targets within three $i_{fib2}$ bins, and the thick black line represents the relationship as measured on the whole LOWZ sample. Error bars show Poisson errors. Unlike what is observed for the fainter CMASS sample (see RossEtAl12), we see no coherent trend of target density with stellar density. Top panel: Distribution of LOWZ targets according to angular stellar density.
  • Figure 4: Fluctuations of on-sky angular target density for the NGC (red lines), SGC (blue lines) and their combination (purple circles), as a function of angular stellar density, $r$-band extinction, $i$-band sky background, airmass in the $i$ band, and seeing in the $i$ band, from left to right. No significant trends are apparent.
  • Figure 5: Weighted galaxy number density for LOWZ galaxies as a function of redshift for the NGC and SGC (solid lines, lower and upper respectively). The dashed line is the expected number density in the SGC once colour offsets between the two galactic caps, as reported in SchlaflyEtAl11, are taken into consideration. The tension between the two galactic caps is significantly alleviated, but it remains unusual at a $3\sigma$ level - see text for details.
  • ...and 7 more figures