The masses of Local Group dwarf spheroidal galaxies: The death of the universal mass profile

TL;DR

This study challenges the idea of a universal mass profile for dwarf spheroidal galaxies by analyzing a larger sample from both the Milky Way and Andromeda, revealing significant discrepancies and the influence of tidal effects.

Contribution

It provides new evidence that dwarf spheroidal galaxies do not all follow a universal mass profile, especially when considering larger, more diverse samples including Andromeda dSphs.

Findings

Universal mass profile does not fit all dSphs well.

Milky Way and Andromeda dSphs show marginally different profiles.

Outliers with large radii and low velocity dispersions likely affected by tidal interactions.

Abstract

We investigate the claim that all dwarf spheroidal galaxies (dSphs) reside within halos that share a common, universal mass profile as has been derived for dSphs of the Galaxy. By folding in kinematic information for 25 Andromeda dSphs, more than doubling the previous sample size, we find that a singular mass profile can not be found to fit all the observations well. Further, the best-fit dark matter density profile measured for solely the Milky Way dSphs is marginally discrepant (at just beyond the 1 sigma level) with that of the Andromeda dSphs, where a profile with lower maximum circular velocity, and hence mass, is preferred. The agreement is significantly better when three extreme Andromeda outliers, And XIX, XXI and XXV, all of which have large half-light radii (>600pc) and low velocity dispersions (sigma_v < 5km/s) are omitted from the sample. We argue that the unusual properties of these outliers are likely caused by tidal interactions with the host galaxy.