M31’s Dwarf Galaxy Building Blocks Raja Guhathakurta University of California Observatories / University of California Santa Cruz Wed Aug 29, 2007 Ann Arbor, Michigan The Globular Clusters-Dwarf Galaxies Connection workshop

Outline Studying the Building Process in Detail   Reconstruction of a recent collision: giant southern stream, shells, etc   Ongoing tidal disruption of NGC 205: constraining the orbit and properties of the progenitor M31’s Extended Stellar Halo Intrinsic Properties of the Dwarfs Tracers of M31’s Gravitational Potential and Tangential Motion

Karrie Gilbert, Jason Kalirai, Kirsten Howley, Evan Kirby, Ryan Montgomery, Greg Laughlin (UCSC) Mark Fardal (U Mass), Marla Geha (HIA/NRC) Steve Majewski, Rachael Beaton, Jamie Ostheimer, Ricky Patterson, Ricardo Muñoz (U Virginia) David Reitzel, Mike Rich (UCLA), Michael Cooper (UC Berkeley) Arif Babul, Alan McConnachie (U Victoria) James Bullock, Marc Seigar (UC Irvine) Andreea Font (Durham), Kathryn Johnston (Columbia U) Phil Choi (Pomona), Roeland van der Marel (STScI) Collaborators

Dissecting a Recent Collision

Giant Stream and Young Shell System in M31 Giant S Stream NE Shelf W Shelf Fardal et al. (2007, MNRAS) Star-Count Map (Irwin et al. 2005)

Dissecting a Recent Collision in M31 Fardal et al. (2007, MNRAS) Simulation Data The debris and shells from this collision provide a natural explanation of the Brown et al. (2003, 2006, 2007) findings on stellar age / metallicity distributions from ultra-deep HST/ACS studies of the MSTO Gilbert et al. (2007, ApJ, in press)

Properties of Dwarf Galaxy Progenitor of M31’s Giant Stream (work in progress) Fardal et al. (2007, in prep) Ibata et al. (2007, ApJ, subm)

Tidal Disruption of NGC 205

NGC 205 Observations Keck / DEIMOS multislit spectroscopy Integrated light spectra cannont probe beyond effective radius We have targeted individual red giant branch stars Accurate radial velocities for 723 red giant stars in NGC 205 Choi, PG & Johnston (2002, AJ) Geha, PG, Rich & Cooper (2006, AJ)

Keck / DEIMOS Targets

Radius (arcmin) Radial velocity (km/s) NGC 205: Major-axis Velocity Profile Geha, PG, Rich & Cooper (2006, AJ) Howley et al. (in prep) Inner rotation speed: ≈ 10 km/s Radial velocity curve turns over beyond 2.5 r eff (≈ r tidal ) Velocity turnover is coincident with radius at which isophotal twisting starts to occur Dynamical modelling using a genetic algorithm indicates that NGC 205 is approaching from the NW, on a highly radial orbit, likely on an unbound orbit on its first close passage. Observations can be reproduced with a dynamically hot, but rotating progenitor.

M31 ’ s Extended Stellar Halo

165 kpc Majewski/Ostheimer KPNO 4-m/MOSAIC DDO51 filter Remote Outer Halo of M31 Ostheimer (2002, PhD thesis) Beaton et al. (in prep) Kalirai et al. (2006a)

We use probability distribution functions based on five photometric / spectroscopic diagnostics to eliminate foreground Milky Way dwarf stars. We plan use five more diagnostics in the near future. (1) Radial Velocity (2) DDO51 photometry (3) Na I equivalent width (4) Position in the CMD (5) [Fe/H] phot vs [Fe/H] spec (6–7) K I line strengths (8–10) TiO band strengths Gilbert et al. (2006, ApJ) Isolating a clean sample of M31 RGB stars

Counts of spectroscopically confirmed M31 RGB stars in outer fields (R = 30 to 150 kpc) lie well above extrapolation of Sersic-law inner spheroid; Best fit: R -2 power law halo PG et al. (2005, astro-ph/ ) PG et al. (2007, ApJ, in prep) Surface Brightness Profile of M31

Dwarf Satellite Tracers

Dwarf Spheroidal Building Blocks Keck/DEIMOS studies of And I, II, and III Kalirai et al. (2007, ApJ, in prep)

Dwarf Spheroidal Building Blocks The discovery of an M31 dSph satellite with extreme orbital properties: And XIV ! — Majewski et al. (2007, ApJL, submitted; astro-ph/ ) — Geha et al. (in prep)

The Metal-Poor Halo of the Andromeda Spiral Galaxy M31 Image from GALEX Feb. 7 th, 2006 Local Group Cosmology, Aspen CO Size of M31 halo!

Tangential Motion of the M31 System The large angular size of the M31 halo implies that the mean tangential motion of the system (parent galaxy + dwarf satellites) should be apparent in the distribution of line-of-sight velocities

Tangential Motion of the M31 System van der Marel & PG (2007, ApJ, in prep) Using Dwarf Satellite Dynamics

Summary Reconstructing M31’s giant southern stream   Single event  stream, 3 shells, minor axis features   Strong constraint on M31 potential   Stream asymmetry requires rotating progenitor   Need radial metallicity gradient in the progenitor Ongoing tidal disruption of dE NGC 205   Unbound orbits, first-time infall favored   Need dynamically hot progenitor with some rotation Tangential motion of the M31 subgroup   Extended stellar halo kinematics   Extended population of dwarf satellites / star clusters