Dark Energy Survey Year 3 results: galaxy sample for BAO measurement

ABSTRACT In this paper, we present and validate the galaxy sample used for analysis of baryon acoustic oscillation (BAO) signal in Dark Energy Survey (DES) Y3 data. The definition is based on a colour redshift-dependent magnitude cut optimized to select galaxies at redshifts higher than 0.5, while ensuring high-quality determination. covers ${\sim }\, 4100$ deg2to depth i = 22.3 (AB) 10?. It contains 7031 993 redshift range from $z$ 0.6 1.1, with mean effective 0.835. Redshifts are estimated machine learning algorithm dnf, validated using VIPERS PDR2 sample. We find bias $z_{\mathrm{bias}} {\sim 0.01$ uncertainty, units 1 + $z$, $\sigma _{68} 0.03$. evaluate population sample, showing it mostly built upon Elliptical Sbc types. Furthermore, low level stellar contamination $\lesssim 4{{\ \rm per\ cent}}$. method mitigate effect spurious clustering coming observing conditions other large-scale systematics. apply BAO calculate weights that get robust estimate signal. This paper one series dedicated DES Y3. companion papers, mock catalogues calibrate angular diameter distance constraints obtained through fitting scale.