Phase Space Models of the Dwarf Spheroidal Galaxies

TL;DR

This paper develops new phase-space models for dwarf spheroidal galaxies using isotropic, lowered isothermal distributions, showing they fit observed data well and yield consistent mass estimates across different dark matter profiles.

Contribution

The paper introduces physically motivated phase-space models for dSphs that reconcile observed velocity dispersions with various dark matter halo profiles, demonstrating robustness of mass estimates.

Findings

Models reproduce observed half-light radii and velocity dispersions.

Mass estimates are similar across cored and cusped dark matter profiles.

Most massive dSphs are the most luminous, like Sagittarius and Fornax.

Abstract

This paper introduces new phase-space models of dwarf spheroidal galaxies (dSphs). The stellar component has an isotropic, lowered isothermal (or King) distribution function. A physical basis for the isotropization of stellar velocities is given by tidal stirring, whilst the isothermality of the distribution function guarantees the observed flatness of the velocity dispersion profile in the inner parts. Our models reproduce the data on the half-light radius and line of sight central velocity dispersion of the dSphs. We show that different dark halo profiles -- whether cored or cusped -- lead to very similar mass estimates within one particular radius, namely 1.7 half-light radii. Deviations between mass measures due to different density profiles are substantially smaller than the uncertainties propagated by the observational errors. We produce a mass measure for each of the Milky Way dSphs and find that the two most massive are the most luminous, namely Sagittarius (~ 2.8 x 10^8 solar masses) and Fornax (~ 1.3 x 10^8 solar masses). The least massive of the Milky Way satellites are Willman 1 (~ 4 x 10^5 solar masses) and Segue 1 (~ 6 x 10^5 solar masses).