Stellar Velocities in the Carina, Fornax, Sculptor and Sextans dSph Galaxies: Data from the Magellan/MMFS Survey

TL;DR

This study provides extensive spectroscopic data for stars in four dwarf spheroidal galaxies, enabling analysis of their velocities and metallicities to understand galaxy membership and contamination.

Contribution

The paper presents a large dataset of stellar spectra and velocities for four dSph galaxies, with calibrated metallicity indicators and a method for membership probability assessment.

Findings

Over 8,800 spectra obtained from 7,103 stars.

Identification of more than 5,000 galaxy members across the four dSphs.

Calibration of spectral indices as relative metallicity indicators.

Abstract

We present spectroscopic data for individual stars observed from 2004 March through 2008 August as part of our Michigan/MIKE Fiber System (MMFS) survey of four dwarf spheroidal (dSph) galaxies: Carina, Fornax, Sculptor and Sextans. Using MMFS at the Magellan/Clay Telescope at Las Campanas Observatory, we have acquired 8855 spectra from 7103 red giant candidates in these Galactic satellites. We list measurements of each star's line-of-sight velocity (median error +/- 2.1 km/s) and spectral line indices for iron and magnesium absorption features. We use globular cluster spectra to calibrate the indices onto standard [Fe/H] metallicity scales, but comparison of the resulting metallicities with published values suggests that the MMFS indices are best used as indicators of relative, not absolute metallicity. The empirical distributions of velocity and spectral indices also allow us to quantify the amount of contamination by foreground stars. In a companion paper we develop an algorithm that evaluates the membership probability for each star, showing that the present MMFS sample contains more than 5000 dSph members, including 774 Carina members, 2483 Fornax members, 1365 Sculptor members, and 441 Sextans members.