Biases in mass estimates of dSph galaxies

TL;DR

This study uses high-resolution simulations to identify how tidal interactions cause biases in mass estimates of dwarf spheroidal galaxies, affecting observational interpretations.

Contribution

It reveals two main effects—tidal tail contamination and non-spherical shapes—that bias mass estimates in dwarf galaxies due to tidal interactions.

Findings

Tidal tails contaminate kinematic samples, inflating velocity dispersion and mass estimates.

Non-spherical stellar distributions cause orientation-dependent mass over- or underestimates.

Tidal stirring transforms stellar disks into spheroids, affecting shape-based mass measurements.

Abstract

Using a high resolution N-body simulation of a two-component dwarf galaxy orbiting in the potential of the Milky Way, we study two effects that lead to significant biases in mass estimates of dwarf spheroidal galaxies. Both are due to the strong tidal interaction of initially disky dwarfs with their host. The tidal stripping of dwarf stars leads to the formation of strong tidal tails that are typically aligned with the line of sight of an observer positioned close to the host center. The stars from the tails contaminate the kinematic samples leading to a velocity dispersion profile increasing with the projected radius and resulting in an overestimate of mass. The tidal stirring of the dwarf leads to the morphological transformation of the initial stellar disk into a bar and then a spheroid. The distribution of stars in the dwarf remains non-spherical for a long time leading to an overestimate of its mass if it is observed along the major axis and an underestimate if it seen in the perpendicular direction.