Overview of the DESI Milky Way Survey

TL;DR

The DESI Milky Way Survey aims to observe around seven million stars over five years to enhance understanding of Galactic structure and stellar evolution, utilizing advanced pipelines for precise measurements.

Contribution

This paper introduces the DESI MWS project, detailing its target selection, data pipelines, and initial validation results, marking a significant step in Galactic surveys.

Findings

Radial velocities measured to ~1 km/s accuracy.

Stellar parameters with ~0.2 dex [Fe/H] accuracy.

Good agreement with mock catalogs and previous surveys.

Abstract

We describe the Milky Way Survey (MWS) that will be undertaken with the Dark Energy Spectroscopic Instrument (DESI) on the Mayall 4m telescope at the Kitt Peak National Observatory. Over the next 5 yr DESI MWS will observe approximately seven million stars at Galactic latitudes |b|>20 degrees, with an inclusive target selection scheme focused on the thick disk and stellar halo. MWS will also include several high-completeness samples of rare stellar types, including white dwarfs, low-mass stars within 100pc of the Sun, and horizontal branch stars. We summarize the potential of DESI to advance understanding of Galactic structure and stellar evolution. We introduce the final definitions of the main MWS target classes and estimate the number of stars in each class that will be observed. We describe our pipelines for deriving radial velocities, atmospheric parameters, and chemical abundances. We use ~500,000 spectra of unique stellar targets from the DESI Survey Validation program (SV) to demonstrate that our pipelines can measure radial velocities to ~1 km/s and [Fe/H] accurate to ~0.2 dex for typical stars in our main sample. We find the stellar parameter distributions from ~100 sq. deg of SV observations with >90% completeness on our main sample are in good agreement with expectations from mock catalogs and previous surveys.