AAS 201st Meeting, January, 2003
Session 14. Galaxy - Contents
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[14.13] Keck Spectroscopy of Red Giants in the M31 dSph Satellites: Dynamics

L. Pittroff (MPI for Extraterrestrial Physics, Germany), P. Guhathakurta, S. Datta (UCO/Lick Obs, UCSC), E. Grebel (MPI for Astronomy, Germany), S. Vogt (UCO/Lick Obs, UCSC)

The recent discovery of three dwarf spheroidal (dSph) satellites at large projected distances (several 100 kpc) from M31 has provided new dynamical tracers of the extended dark matter halo of the parent galaxy. Radial velocities are measured for five M31 dSphs using the Keck 10-meter telescope and the Low Resolution Imaging Spectrometer (see Datta et al. companion poster for details of the observations) and the High Resolution Echelle Spectrometer (HIRES). Line-of-sight distances are estimated from measurements of the tip of the red giant branch. These data, in conjunction with available data on other dynamical tracers, indicate that M31 may be less massive than the Milky Way (Evans et al. 2000). A plot is presented showing the lower limit to the enclosed mass of M31 as a function of radius based on a ``minimum circular velocity'' assumption for the tracers. We speculate on the basis of this diagram that LGS3 is near the apocenter of a plunging orbit around M31.

In contrast to other low luminosity hot stellar systems such as globular clusters, dwarf ellipticals, and low luminosity ellipticals which contain little or no dark matter within their optical extent, dSph galaxies appear to be dark-matter-dominated. Thus, dSphs are good test beds for studying the properties of small dark matter halos. We apply a new multi-slit echelle spectroscopy technique to 21 red giant candidates in the M31 satellite Cas dSph (And VII) using Keck/HIRES. The radial velocities measured from these data have an rms spread of about 9 km/s. Dynamical modelling of these data is in progress to determine the M/L ratio.

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