The effect of unbound stars on the mass modelling of the Fornax dwarf

TL;DR

This paper examines how the selection of member stars influences mass estimates in dwarf spheroidal galaxies, highlighting the importance of contamination and velocity distribution analysis for accurate modeling.

Contribution

It introduces a method to account for member star selection effects and demonstrates the impact of Milky Way contamination on Fornax galaxy mass modeling.

Findings

Member star selection significantly affects mass estimates.

Including kurtosis improves parameter constraints.

Most contamination in Fornax likely from Milky Way stars.

Abstract

We discuss how different approaches to selecting member stars in kinematic samples of dwarf spheroidal galaxies affect the estimates of their mass and anisotropy of stellar orbits. We demonstrate that the selection of members is an additional source of error compared to the usual uncertainties due to the sampling of velocity moments. As an example we use the kinematic data set for 202 stars in the Fornax dwarf galaxy for which we model the velocity dispersion profile and estimate the mass-to-light ratio and anisotropy assuming that mass follows light. We also show that stronger constraints on these parameters can be obtained if kurtosis of the velocity distribution is included in the analysis. Using the Besancon model of the Milky Way we demonstrate that the majority of contamination in Fornax probably comes from the Milky Way stars.