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The SPLASH Survey: Kinematics of Andromeda's Inner Spheroid | | Claire E. Dorman
; Puragra Guhathakurta
; Mark A. Fardal
; Dustin Lang
; Marla C. Geha
; Kirsten M. Howley
; Jason S. Kalirai
; James S. Bullock
; Jean-Charles Cuillandre
; Julianne J. Dalcanton
; Karoline M. Gilbert
; Anil C. Seth
; Erik J. Tollerud
; Benjamin F. Williams
; Basilio Yniguez
; | | Date: |
19 Apr 2012 | | Abstract: | The combination of large size, high stellar density, high metallicity, and
Sersic surface brightness profile of the spheroidal component of the Andromeda
galaxy (M31) within R_proj ~ 20 kpc suggest that it is unlike any subcomponent
of the Milky Way. In this work we capitalize on our proximity to and external
view of M31 to probe the kinematical properties of this "inner spheroid." We
employ a Markov chain Monte Carlo (MCMC) analysis of resolved stellar
kinematics from Keck/DEIMOS spectra of 5651 red giant branch stars to
disentangle M31’s inner spheroid from its stellar disk. We measure the mean
velocity and dispersion of the spheroid in each of five spatial bins after
accounting for a locally cold stellar disk as well as the Giant Southern Stream
and associated tidal debris. For the first time, we detect significant spheroid
rotation (v_rot ~ 50 km/s) beyond R_proj ~ 5 kpc. The velocity dispersion
decreases from about 140 km/s at R_proj = 7 kpc to 120 km/s at R_proj = 14 kpc,
consistent to 2 sigma with existing measurements and models. We calculate the
probability that a given star is a member of the spheroid and find that the
spheroid has a significant presence throughout the spatial extent of our
sample. Lastly, we show that the flattening of the spheroid is due to velocity
anisotropy in addition to rotation. Though this suggests that the inner
spheroid of M31 more closely resembles an elliptical galaxy than a typical
spiral galaxy bulge, it should be cautioned that our measurements are much
farther out (2 - 14 r_eff) than for the comparison samples. | | Source: | arXiv, 1204.4455 | | Services: | Forum | Review | PDF | Favorites | |
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