The Extended Stellar Halo of the Andromeda Spiral Galaxy and its Dwarf Satellites: Results from the SPLASH Survey

Puragra (Raja) Guhathakurta

Detailed studies of nearby galaxies provide vital clues about their formation and evolutionary history. This fossil record approach is complementary to direct look-back studies of distant galaxies. Our Galaxy and the Andromeda spiral galaxy (M31) have long been cornerstones in the former category. M31 provides an external perspective on a large galaxy similar to our own and yet is close enough to allow detailed studies of individual stars.

I will present results from a large international collaboration: SPLASH - Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo. The SPLASH survey data set includes:

1. Spectroscopy of individual luminous red giant branch stars with Keck and DEIMOS
2. Ground-based wide-field imaging and photometry, most recently with KPNO/Mosaic, CFHT/MegaCam, and Subaru/Suprime-Cam
3. Deep Hubble Space Telescope imaging, including ultradeep imaging reaching below the main-sequence turnoff

Our recent discovery of an extended stellar halo in M31 (R > 150 kpc) shows that most previous studies of its spheroid have been sampling its inner bulge-like spheroidal component, not its halo. In my talk I will touch upon several related topics including: M31's global structure and subcomponents (halo, bulge/central bar, and disk), statistics of substructure, chemical abundance constraints, detailed reconstruction of recent collision events, dwarf satellites as tracers and building blocks of larger galaxies, and empirical constraints on the tangential motion of the M31 system.