Preliminary Target Selection for the DESI Emission Line Galaxy (ELG) Sample

TL;DR

This paper details a preliminary method for selecting Emission Line Galaxy targets for DESI, aiming to optimize redshift measurements crucial for understanding cosmic expansion and structure growth.

Contribution

It introduces a specific color and magnitude-based selection method for ELGs, validated with existing photometric and spectroscopic data, to improve target efficiency for DESI.

Findings

ELG target density estimated at ~2400 per square degree.

Approximately 65% of ELGs will have reliable redshifts within 0.6<z<1.6.

Selection method validated with HSC/PDR2 and DEEP2 data.

Abstract

DESI will precisely constrain cosmic expansion and the growth of structure by collecting $\sim$35 million redshifts across $\sim$80% of cosmic history and one third of the sky to study Baryon Acoustic Oscillations (BAO) and Redshift Space Distortions (RSD). We present a preliminary target selection for an Emission Line Galaxy (ELG) sample, which will comprise about half of all DESI tracers. The selection consists of a $g$-band magnitude cut and a $(g-r)$ vs. $(r-z)$ color box, which we validate using HSC/PDR2 photometric redshifts and DEEP2 spectroscopy. The ELG target density should be $\sim$2400 deg$^{-2}$, with $\sim$65% of ELG redshifts reliably within a redshift range of $0.6<z<1.6$. ELG targeting for DESI will be finalized during a `Survey Validation' phase.