Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.2606g&link_type=abstract
American Astronomical Society, AAS Meeting #211, #26.06; Bulletin of the American Astronomical Society, Vol. 39, p.777
Astronomy and Astrophysics
Astronomy
Scientific paper
The SPLASH (Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo) collaboration has obtained spectra using Keck/DEIMOS of several thousand red giant stars in M31's extended stellar halo and its dwarf satellites. Our M31 fields of study span a few tens of degrees on the sky. If the M31 system has a substantial velocity component in the tangent plane (orthogonal to the line of sight to center of M31), this tangential motion imprints a characteristic pattern on the mean radial velocity of stars in these remote fields as a function of their angular distance from M31's center and position angle. We use a combination of photometric and spectroscopic diagnostics to reliably separate red giants in M31 from foreground Milky Way dwarf star contaminants (see Gilbert et al. 2006); this step is critical because M31 red giants are very rare in these remote fields. The resulting radial velocity distribution of field red giants in M31's extended stellar halo and the radial velocity distribution of M31's dwarf satellites are used to place strong constraints on the tangential motion of the M31 subgroup. These constraints are compared to water maser-based proper motion measurements in the M31 satellites M33 and IC10 and to constraints on the motion of the Local Group barycenter derived from remote satellites located near the "zero velocity" surface of the Local Group. Finally, we discuss the implications of these tangential motion measurements on the dynamics of the Local Group.
This research is supported by NSF grant AST-0607852.
Beaton Rachael Lynn
Geha Marla C.
Gilbert Karoline M.
Guhathakurta Puragra
Kalirai Jason S.
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