Defining the DESI Bright Galaxy Survey target selection

Abstract

This thesis aims to cover the steps taken for the selection of the input galaxy catalogue for the Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey (BGS) using the photometric Legacy Surveys. The BGS is a redshift survey of bright galaxies that will be performed using the DESI 5,000 fibre spectrograph on the 4m Mayall telescope in at Kitt Peak, Arizona. Our galaxy selection implements a new way to perform star galaxy separation using the Gaia photometry. The purity of our sample is assessed with previous galaxy surveys GAMA and the SDSS Main Galaxy Sample, and with the MXXL light-cone mock catalogue through clustering measurements. The robustness of the BGS selection criteria are assessed by quantifying the dependence of the target galaxy density on imaging and other properties. Systematic correlations are found with amplitudes of less than 5 per cent. This work also presents the first results from the Survey Validation (SV) stage of DESI. Using the SV data we were able to assess our BGS selection and tune it to achieve a high redshift success rate. The final catalogue includes nearly 30 Million galaxies for a 14,000 deg2 area that covers the North and South Galactic Caps.