Authors: Julio Chaname, Marla Geha, & Roeland van der Marel
The three dwarf elliptical (dE) galaxies of the Local Group constitute our best chance to learn about the total mass distributions and internal dynamics of this type of objects. As a class, dE's may constitute the bright extension of the more ubiquituous dwarf spheroidals, the most dark matter dominated objects we know of, and thus it is important to determine whether there are any connections. However, kinematically speaking, they have not been studied in enough detail yet, and most of the current constraints on the dark matter content of dE's come from members of galaxy clusters. Moreover, all of these are restricted to mass-to-light ratio measurements made at small galactocentric radii, thus being possibly more indicative of the characteristics of their stellar populations than of their true dark matter halos, which are most effectively probed by discrete kinematic tracers at large radii. We will present results from our ongoing study of the internal dynamics of NGC 147 and NGC 185, dE satellites of Andromeda showing no apparent signs of tidal interaction with their giant host. The data are comprised of recent Keck DEIMOS radial velocity measurements of hundreds of red giants out to 10 effective radii in the two galaxies, and we will show preliminary results of our orbit-based dynamical modeling, specifically aimed to take advantage of the discrete nature of the data as well as to avoid oversimplifying assumptions on the form of the stellar distribution function and the degree of (an)isotropy of the orbits. The combination of our state-of-the-art models and data will soon provide the strongest constraints to date on the dark halos of dE galaxies.
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