Tailored mass estimators for Milky Way dwarf Spheroidals

TL;DR

This paper develops flexible mass estimators for Milky Way dwarf spheroidal galaxies by accounting for uncertainties in stellar density profiles, revealing large potential systematic errors in traditional dynamical mass estimates and their scaling relations.

Contribution

It introduces a method to incorporate shape uncertainties of stellar profiles into mass estimates, improving the accuracy of dynamical inferences for dSph galaxies.

Findings

Standard mass estimators can be off by factors of 10 due to profile shape assumptions.

Accounting for uncertainties alters the observed dynamical scaling relations.

Structural diversity in dSphs leads to significant systematic errors in mass estimates.

Abstract

Assuming spherical symmetry and dynamical equilibrium within a given gravitational potential, a dwarf spheroidal (dSph) galaxy's globally averaged stellar velocity dispersion depends entirely on the shape of its stellar density profile. Thus, the dynamical inference of a dSph's gravitational potential is necessarily sensitive to assumptions about that shape. Relaxing standard assumptions, we fit flexible stellar density models to observations of the Milky Way's known dSph satellites. Considering various choices for the density profile shape and spatial extent of a host dark matter halo, we use the virial theorem to propagate observational uncertainties about the shapes of the inferred dSph stellar density profiles to uncertainties in the inferred dynamical masses. We find that the observed structural diversity of the Milky Way dSph population implies a large range of potential systematic errors (up to factors of 10) associated with standard dynamical mass estimators. We show that accounting for these observational and systematic uncertainties can significantly alter the appearance and behavior of dSph dynamical scaling relations, including enclosed dynamical mass vs. stellar mass and the Radial Acceleration Relation.