The Clustering of Luminous Red Galaxies in the Sloan Digital Sky Survey Imaging Data

TL;DR

This work demonstrates that a large, photometrically redshifted galaxy sample can yield a precise 3D real-space power spectrum, enabling robust cosmological inferences from a purely imaging survey. By carefully calibrating photometry, selecting luminous red galaxies with well-characterized redshift distributions, and stacking eight angular power spectra, the authors detect large-scale power and baryon acoustic oscillations, constrain $\Omega_M$ to ~0.30 and $\Omega_b/\Omega_M$ to ~0.18, and measure a 6.5% distance to $z=0.5$. The analysis also shows that photometric surveys can provide competitive cosmological constraints and that BAO features in galaxy clustering serve as a useful standard ruler, with results consistent with CMB-derived parameters. This work paves the way for future wide-field imaging surveys to contribute meaningfully to dark energy studies and large-scale structure physics.

Abstract

We present the 3D real space clustering power spectrum of a sample of \~600,000 luminous red galaxies (LRGs) measured by the Sloan Digital Sky Survey (SDSS), using photometric redshifts. This sample of galaxies ranges from redshift z=0.2 to 0.6 over 3,528 deg^2 of the sky, probing a volume of 1.5 (Gpc/h)^3, making it the largest volume ever used for galaxy clustering measurements. We measure the angular clustering power spectrum in eight redshift slices and combine these into a high precision 3D real space power spectrum from k=0.005 (h/Mpc) to k=1 (h/Mpc). We detect power on gigaparsec scales, beyond the turnover in the matter power spectrum, 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 sigma confidence level. 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 Ω_M = 0.30 \pm 0.03, and Ω_b/Ω_M = 0.18 \pm 0.04, The detection of baryonic oscillations also allows us to measure the comoving distance to z=0.5; we find a best fit distance of 1.73 \pm 0.12 Gpc, corresponding to a 6.5% error on the distance. These results demonstrate the ability to make precise clustering measurements with photometric surveys (abridged).

Figures (27)

• Figure 1: A model spectrum of an elliptical galaxy, taken from Bruzual & Charlot (2003MNRAS.344.1000B), shown at three redshifts. The model assumes a single burst of star formation 11 Gyr ago and solar metallicity; the effect of evolution is not shown for simplicity. Also overplotted are the response functions (including atmospheric absorption) for the five SDSS filters. The break in the spectrum at 4000 Å, and its migration through the SDSS filters is clearly seen.
• Figure 2: The top panel shows simulated $g-r$ and $r-i$ colours of an early-type galaxy as a function of redshift. The spectrum used to generate the track is the same as in Fig. \ref{['fig:lrg_spectrum']}, but evolved in redshift. Also shown are the colour cuts for Cut I (dashed, black) and Cut II galaxies (solid, blue). The lower panel shows the colours $c_{||}$ (diamonds, black) and $d_{\perp}$ (triangles, red), as a function of redshift. Also shown are fiducial redshift boundaries for Cut I (0.2 -- 0.4) and Cut II (0.4 -- 0.6). Note that the range in $g-r$ is identical to the range in $1+z$.
• Figure 3: The angular selection function of the LRGs with the "Northern Celestial Cap" (black) and the "Equatorial Cap" (blue) shown. The lightly shaded (green) region of the Equatorial cap ($b < 45^{\circ}$, shown as a dashed line) is excluded because of possible stellar contamination. The gaps in the selection function are due to missing data and exclusion around bright stars. Also shown is the Galactic equator (solid line).
• Figure 4: (Top) The photometric redshift distribution of the LRG sample. (Bottom) The deconvolved selection functions for photometric redshift slices with $\Delta z=0.05$ from $z=0.2$ to $z=0.6$. The dotted lines are the mean redshifts of each of the slices.
• Figure 5: The average number of LRGs per resolution 6 HEALPix pixel (approximately $1\,{\rm deg}^{2}$ in area) as a function of Galactic latitude, for the two disjoint caps. The contours are 16%, 50% and 84%. There is some evidence for stellar contamination (see text for more details) at low Galactic latitudes in the Equatorial Cap; excising the region $b < 45^{\circ}$ removes the problematic regions.