The SDSS-IV extended Baryonic Oscillation Spectroscopic Survey: Luminous Red Galaxy Target Selection

TL;DR

This paper details the selection algorithm for Luminous Red Galaxy targets in the eBOSS survey, achieving high redshift accuracy and low contamination, enabling large-scale structure studies at higher redshifts.

Contribution

The paper introduces an effective target selection algorithm combining SDSS and WISE data, optimized for high-redshift LRGs with low stellar contamination and reliable redshift measurements.

Findings

Approximately 50 LRGs per square degree selected

89% of targets yield secure redshifts

Sample is uniform and suitable for large-scale structure analysis

Abstract

We describe the algorithm used to select the Luminous Red Galaxy (LRG) sample for the extended Baryon Oscillation Spectroscopic Survey (eBOSS) of the Sloan Digital Sky Survey IV (SDSS-IV) using photometric data from both the SDSS and the Wide-Field Infrared Survey Explorer (WISE). LRG targets are required to meet a set of color selection criteria and have z-band and i-band MODEL magnitudes z < 19.95 and 19.9 < i < 21.8, respectively. Our algorithm selects roughly 50 LRG targets per square degree, the great majority of which lie in the redshift range 0.6 < z < 1.0 (median redshift 0.71). We demonstrate that our methods are highly effective at eliminating stellar contamination and lower-redshift galaxies. We perform a number of tests using spectroscopic data from SDSS-III/BOSS to determine the redshift reliability of our target selection and its ability to meet the science requirements of eBOSS. The SDSS spectra are of high enough signal-to-noise ratio that at least 89% of the target sample yields secure redshift measurements. We also present tests of the uniformity and homogeneity of the sample, demonstrating that it should be clean enough for studies of the large-scale structure of the universe at higher redshifts than SDSS-III/BOSS LRGs reached.