Target Selection oF Emission-Line Galaxies in DESI

Motivation

Emission-Line Galaxies (ELGs) form the bulk of the DESI survey. All the ELGs in the DESI survey ought to be in the redshift range $0.6 <z < 1.6$. To ensure the redshift, DESI conducted an imaging survey in $g$, $r$ and $z$ bands called the Legacy Surveys that covers 14,000 deg$^2$. The goal and the challenge is to use the colour information, i.e., $g - r$ vs. $r - z$, to determine which ELGs meet the DESI redshift range and the minimum flux requirement. These procedure is known as target selection.

Three different ELG target selection algorithms were proposed within DESI in 2017. In this project, I conducted a mini DESI-like survey using the Binospec spectrograph at the MMT where I selected ELG targets using these target selection algorithms. I measured the overall redshift quality and success rate of these algorithms and published a catalogue of $1800$ ELG redshifts. Based on my analysis, I proposed a simple modification to one of the target selection algorithms that best meet the DESI requirements. This suggestion has been subsequently implemented in the main DESI survey, which has been operational since Summer 2021.

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