Luminous Red Galaxies: Selection and classification by combining optical and infrared photometry

TL;DR

This paper introduces a novel method combining optical and infrared photometry to efficiently select high-redshift Luminous Red Galaxies with minimal stellar contamination, enhancing galaxy survey capabilities.

Contribution

The paper presents a new combined photometric selection technique for LRGs at z > 0.6, optimized using multi-region testing and applied to major galaxy surveys.

Findings

Efficient high-redshift LRG selection with minimal stellar contamination.

Method successfully applied to SDSS-III/BOSS and SDSS-IV/eBOSS surveys.

Adaptable approach for future surveys like DESI.

Abstract

We describe a new method of combining optical and infrared photometry to select Luminous Red Galaxies (LRGs) at redshifts $z > 0.6$. We explore this technique using a combination of optical photometry from CFHTLS and HST, infrared photometry from the WISE satellite, and spectroscopic or photometric redshifts from the DEEP2 Galaxy Redshift Survey or COSMOS. We present a variety of methods for testing the success of our selection, and present methods for optimization given a set of rest-frame color and redshift requirements. We have tested this selection in two different regions of the sky, the COSMOS and Extended Groth Strip (EGS) fields, to reduce the effect of cosmic/sample variance. We have used these methods to assemble large samples of LRGs for two different ancillary programs as a part of the SDSS-III/ BOSS spectroscopic survey. This technique is now being used to select $\sim$600,000 LRG targets for SDSS-IV/eBOSS, which began observations in Fall 2014, and will be adapted for the proposed DESI survey. We have found these methods can select high-redshift LRGs efficiently with minimal stellar contamination; this is extremely difficult to achieve with selections that rely on optical photometry alone.