Stellar reddening map from DESI imaging and spectroscopy

TL;DR

This paper introduces new Galactic dust reddening maps using DESI data, revealing significant differences from previous maps and demonstrating improved extinction correction accuracy for extragalactic studies.

Contribution

It provides the first high-latitude reddening maps based on DESI stellar data, highlighting systematic differences from the SFD map and validating improved extinction corrections.

Findings

Reddening maps differ from SFD by up to 80 mmag in E(B-V).

Reddening measurements are consistent with Fitzpatrick extinction curve.

Extinction correction using these maps improves galaxy sample uniformity.

Abstract

We present new Galactic dust 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 $R_\mathrm{V}=3.1$. 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 $E(r-z)$ maps presented in this work, and for convenience their corresponding $E(B-V)$ maps with SFD calibration, are publicly available.