Photometric Redshifts and Stellar Masses for Galaxies from the DESI Legacy Imaging Surveys

Abstract

We present new Galactic reddening maps of the high Galactic latitude sky using DESI imaging and spectroscopy. We directly measure the reddening of 2.6 million stars by comparing the observed stellar colors in g − r and r − z from DESI imaging with the synthetic colors derived from DESI spectra from the first two years of the survey. The reddening in the two colors is on average consistent with the Fitzpatrick (1999) extinction curve with R V = 3.1. We find that our reddening maps differ significantly from the commonly used Schlegel et al. (1998) (SFD) reddening map (by up to 80 mmag in E(B − V )), and we attribute most of this difference to systematic errors in the SFD map. To validate the reddening map, we select a galaxy sample with extinction correction based on our reddening map, and this yields significantly better uniformity than the SFD extinction correction. Finally, we discuss the potential systematic errors in the DESI reddening measurements, including the photometric calibration errors that are the limiting factor on our accuracy. The E(g − r) and E(g − r) maps presented in this work, and for convenience their corresponding E(B − V ) maps with SFD calibration, are publicly available.

The Evolutionary Map of the Universe pilot survey

“…An apparent overdensity of galaxies visible in both DES and WISE is embedded in the faint southern emission. However, there is no cataloged cluster near this location, and we found photometric redshifts (Zou et al 2019) for only three galaxies within the source confines that would be consistent with the quasar redshift, so there is no evidence for a cluster.…”

“…There is no major spectroscopic redshift survey covering the EMU-PS field, but a large number of photometric redshifts are available from Bilicki et al (2016) (using their 'main' catalogue), and from Zou et al (2019;, and we also include those in the catalogue. Throughout the rest of this paper, redshifts given without a citation refer to these redshifts used in the EMU-PS catalogue.…”

“…From a preliminary visual inspection of the EMU-PS area, biased towards sources of larger angular size and featuring a radio nucleus, we found ∼120 GRGs larger than 1 Mpc and a similar number with sizes between 0.7 and 1 Mpc. We visually crossidentified these with the DES images and catalogues (Abbott et al 2018) and estimated linear sizes based on photometric redshifts (Bilicki et al 2016;Drlica-Wagner et al 2018;Zou et al 2019). The number of GRGs in EMU-PS is likely to increase with a more thorough visual inspection, the results of which will be reported by Andernach et al (in prep.…”

“…Asterisked rows are shown for information but are not used in the subsequent selection step. Photometric redshifts are taken fromZou et al (2019),Zou et al (2020), andBilicki et al (2016).…”

Radio observations of the merging galaxy cluster system Abell 3391-Abell 3395

“…9. Photometric redshifts were taken from Bilicki et al (2016) and from Zou et al (2019). We measured the flux densities, S , of the GRGs listed in Table 4 within a region marking the 2σ contour line using the local rms for σ.…”