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K. M. Gilbert (UCSC), R. M. Rich, D. B. Reitzel (UCLA), J. S. Kalirai, P. Guhathakurta (UCSC), M. C. Cooper (UC Berkeley), S. R. Majewski (UVa)
We present radial velocities for a large sample of red giant branch (RGB) stars in the Andromeda spiral galaxy (M31) based on Keck/DEIMOS spectroscopy. The stars are drawn from several fields on the SE minor axis of M31 ranging between R=10-30 kpc in projected distance from the center of the galaxy. This region appears to be dominated by the ``bulge-like'' metal-rich spheroid of M31. In particular, we focus on a field that has recently been studied using very deep HST/ACS imaging (Brown et al. 2003, 2005). In this field, Brown et al. found that stars more metal rich than [Fe/H]>-0.5 dex have ages in the range of 6-10 Gyr. We analyze the dynamical properties of the M31 RGB sample and conclude that the intermediate-age population in this field does not arise in a single coherent cold stream, in contrast to fields that intercept the giant southern stream. More distant outer halo fields in M31 may be increasingly dominated by coherent structures, none of which appear to be prominent in the deep HST field.
This research was supported by grants from the NSF and NASA/STScI.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.