The Keck/DEIMOS Stellar Archive: I. Uniform Velocities and Metallicities for 78 Milky Way Dwarf Galaxies and Globular Clusters

TL;DR

This paper provides a comprehensive, uniform spectroscopic dataset of over 22,000 stars in 78 Milky Way dwarf galaxies and globular clusters, enabling improved measurements of velocities and metallicities for astrophysical research.

Contribution

The paper introduces a homogeneous spectroscopic dataset with a new velocity determination method, enhancing accuracy and precision over previous measurements.

Findings

Velocity error floor of 1.1 km/s established

Metallicity error floor of 0.1 dex determined

Improved internal velocity dispersion measurements by 20-50%

Abstract

We present a homogeneous spectroscopic dataset of 22,339 stars in 78 Milky Way dwarf galaxy satellites and globular clusters. All data were taken with the Keck II telescope and Deep Extragalactic Imaging Multiobject Spectrograph (DEIMOS) spectrograph using the 1200G grating (spectral resolution R~6000). Based on a uniform data reduction of 411 DEIMOS masks, we present a catalog of individual stellar radial velocities, equivalent width-based [Fe/H] metallicities, and membership estimates. The Milky Way satellites range from M_V = 2 to -14 (M* = 10^1.5 to 10^7.5 Msun); the majority of individual stars presented in these systems have magnitudes 17 > r > 22. The data were reduced to 1D spectra using PypeIt, which provides near Poisson statistics-level sky subtraction. Radial velocities were determined via dmost, a forward modeling method first presented here, which combines both synthetic telluric and stellar templates to determine stellar radial velocities. We assess the accuracy and precision our method via comparison to thousands of repeat measurements and literature values. We determine a velocity error floor of 1.1 km/s and a CaII triplet-based metallicity error floor of 0.1 dex. We calculate internal velocity dispersions and compare to literature values, demonstrating 20-50% improved precision over the literature in most cases. In a companion paper, we use our homogeneous catalogs to explore properties of these Milky Way satellites, including previously unpublished measurements in several systems including Bootes II and Draco II. We provide full access to the data catalogs to enable further studies.