Velocity Dispersion Profiles of Seven Dwarf Spheroidal Galaxies

TL;DR

This study provides detailed stellar velocity dispersion profiles for seven dwarf spheroidal galaxies, revealing flat profiles indicative of dark matter halos and estimating their masses within specific radii.

Contribution

It presents the largest kinematic data set for these galaxies and models their dark matter halos using NFW profiles, offering new insights into their mass distribution.

Findings

Velocity dispersions are approximately 10 km/s and flat with radius.

Dark matter halos fit NFW profiles with virial masses around 10^8-10^9 solar masses.

Mass within 600 pc ranges from 2 to 7 x 10^7 solar masses.

Abstract

We present stellar velocity dispersion profiles for seven Milky Way dwarf spheroidal (dSph) satellite galaxies. We have measured 8394 line-of-sight velocities (+/- 2.5 km/s) for 6804 stars from high-resolution spectra obtained at the Magellan and MMT telescopes. We combine these new data with previously published velocities to obtain the largest available kinematic samples, which include more than 5500 dSph members. All the measured dSphs have stellar velocity dispersion of order 10 km/s that remains approximately constant with distance from the dSph center, out to and in some cases beyond the radius at which the mean surface brightness falls to the background level. Assuming dSphs reside within dark matter halos characterized by the NFW density profile, we obtain reasonable fits to the empirical velocity dispersion profiles. These fits imply that, among the seven dSphs, M_vir ~ 10^[8-9] M_sun. The mass enclosed at a radius of 600 pc, the region common to all data sets, ranges from (2-7) x 10^7 M_sun .