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

Abstract

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

Dark Energy Survey Year 3 results: A 2.7% measurement of baryon acoustic oscillation distance scale at redshift 0.835

“…We start by applying the same color cut as in Y1 to the Gold sample to select red galaxies. Despite the changes in photometry from Y1 and Y3, the color selection still isolates galaxies at z > 0.5, as attested in [38]. The primary selection includes the aforementioned color cut, a magnitude cut as a function of photometric redshift z photo (to remove fainter galaxies at lower redshifts), and the redshift range.…”

“…The sample covers 4108.47 deg 2 , almost three times larger than the Y1 sample, and comprises 7,031,993 galaxies in the redshift range 0.6 < z < 1.1, up to a magnitude limit of i < 22.3ðAB; 10σ). Full details about the sample selection and characterization is found in [38], here we summarize the main properties.…”

“…In this paper, a new determination of the BAO scale is presented. The measurement uses the imaging data from DES Y3, described in [37], to measure the angular diameter distance to red galaxies that have been specially selected [38] with photometric redshifts 0.6 < z photo < 1.1. DES has imaged a 5; 000 deg 2 footprint of the Southern Hemisphere using five passbands, grizY, collecting the properties of over 300 million galaxies.…”

“…The measurement we present is supported by a series of companion papers. In [38] we present all the details of the selection of the galaxy sample, that was optimized for z > 0.6 BAO measurements, the tests of its basic properties, the mitigation of observational systematic effects, and the photometric redshift validations, extending what was done in [39]. In [40] we describe the mock catalogs we have developed to test the measurement methods.…”

Validating galaxy clustering models with Fixed & Paired and Matched-ICs simulations: application to Primordial Non-Gaussianities

“…Avila et al 2020;Alam et al 2021;Rossi et al 2021), understand the impact of observational systematic effects (e.g. Rosell et al 2022;Spinelli et al 2022) or to compute covariance matrices (e.g. Manera et al 2013;Avila et al 2018;Zhao et al 2021).…”