The internal kinematics of dwarf spheroidal galaxies

TL;DR

This paper surveys the kinematic status of Local Group dwarf spheroidal galaxies, arguing they are dark matter dominated at all radii and are essential tests for dark matter and galaxy formation in a cosmological context. It reviews velocity-dispersion measurements from large stellar samples and discusses dynamical modelling approaches, including Jeans-based mass estimators, under virial equilibrium. The analysis indicates inner halos with shallow central slopes and, across several dSphs, a possible common halo mass around four times ten to the seven solar masses, with masses within observable radii of three to eight times ten to the seven solar masses. The work highlights uncertainties from outer light and kinematic profiles, tidal effects, and the potential role of MOND, and outlines observational and modelling directions for the future.

Abstract

The status of kinematic observations in Local Group dwarf spheroidal galaxies (dSphs) is reviewed. Various approaches to the dynamical modelling of these data are discussed and some general features of dSph dark matter haloes based on simple mass models are presented.

Figures (5)

• Figure 1: Velocity dispersion profiles for the Draco, Ursa Minor and Sextans dSphs (Kleyna et al. 2004; Wilkinson et al. 2004).
• Figure 2: Line of sight velocity versus projected radius for the Ursa Minor data set of Wilkinson et al. (2004), including some non-members. The horizontal lines indicate the 3$\sigma$ velocity cuts used to determine membership. See text for a discussion.
• Figure 3: Surface brightness and velocity dispersion profiles of Draco (Wilkinson et al. 2004). Solid curves show the assumed smooth profiles used in the analysis presented here.
• Figure 4: Circular speed curves (left) and density profiles (right) for four Milky Way dSphs, derived using Jeans equations. From top to bottom the curves show the results for Ursa Minor, Draco, Carina and Sextans. Also shown at the top of each plot are the expected curves for an $r^{-1}$ density distribution. See text for a detailed discussion.
• Figure 5: Mass to light ratios versus absolute magnitudes for Local Group dwarf galaxies. Masses for Phoenix, LeoI, LeoII and Sculptor are taken from Mateo et al. (1998); the mass of AndII is taken from Côté et al. (1999). Recent mass estimates for the remaining dSphs are taken from the sources on these dSphs cited in the main text. See text for a discussion.