The Metal-Poor Halo of the Andromeda Spiral Galaxy Jason Kalirai (University of California at Santa Cruz) Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006 The M31 Team: UCSC - Raja Guhathakurta, Karrie Gilbert & Carynn Luine U. Virginia - Steve Majewski, Jamie Ostheimer, & Ricky Patterson UCLA - Michael Rich & David Reitzel UC Berkeley - Michael Cooper Carnegie Obs. - Marla Geha

The Metal-Poor Halo of the Andromeda Spiral Galaxy Outline: 1.) Recap The disparity between M31’s halo and the Milky Way halo. Predictions from simulations of galaxy formation. 2.) A New Synergistic Survey Deep, wide field imaging. Keck/DEIMOS spectroscopy. Ultra-deep HST/ACS imaging. 3.) First Results Clean detection of M31 RGB stars at R > 150 kpc (Gilbert et al. 2006). Surface Brightness: Bulge vs halo of M31 (Guhathakurta et al. 2006). 4.) Metallicity Distribution Functions Bulge vs Halo [  /Fe] Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy Background - Milky Way vs M31 Properties of Milky Way Halo: Age - old, 12 Gyr Chemical composition - metal poor, [Fe/H] = -1.5 Surface brightness profile - power law, R -2 Properties of M31 Halo: Age - both intermediate age and old populations, 6-12 Gyr Chemical composition - metal rich, [Fe/H] = -0.5 Surface brightness profile - de Vaucouleurs, R 1/4 Brown et al. (2003)Durrell, Harris, & Pritchet (2004) Durrell, Harris, & Pritchet (2001) Bellazzini et al. (2003) Pritchet & van den Bergh (1994) Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006 Bulge:

The Metal-Poor Halo of the Andromeda Spiral Galaxy Simulations of Halo Formation Bullock & Johnston (2004) Predictions: 1.) Substructure in halo. 2.) Chemically distinct outer halo. Observational Requirements: 1.) Spatial coverage. 2.) Chemical distribution. 3.) Ages. Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy M31 Data Sets Deep, Wide-Field Imaging: 1.) CFHT / MegaCam 2.) Kitt Peak / Mosaic DDO51 3.) Subaru / SuprimeCam Spectroscopy: 1.) Keck / DEIMOS (also LRIS) 2.) Gemini / GMOS Ultra-Deep, High Resolution Imaging: 1.) HST / ACS (also WFPC2) Faint RGB LF, HB [Fe/H] phot Sub-structure (starcount maps) Kinematics [Fe/H] spec Elimination of foreground dwarfs Ages HB morphology Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy M31 Data Sets Spectroscopy: 1.) Keck / DEIMOS (also LRIS) 2.) Gemini / GMOS Kinematics [Fe/H] spec Elimination of foreground dwarfs Kalirai et al. (2006, ApJ, submitted) Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy M31 star-count map (Ferguson et al. 2002) Kalirai et al. (2006, ApJ, submitted) M31 Data Sets Spectroscopy: 1.) Keck / DEIMOS (also LRIS) 2.) Gemini / GMOS Kinematics [Fe/H] spec Elimination of foreground dwarfs Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy Isolating a clean sample of M31 RGB stars Use probability distribution functions based on 5 photometric/spectroscopic diagnostics to eliminate foreground Milky Way dwarfs. 1.) Radial Velocity 2.)DDO51 photometry 3.) Na I equivalent width 4.) Position in the CMD 5.) [Fe/H] phot vs [Fe/H] spec Gilbert et al. (2006, in prep.) Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

Outer Halo of M kpc Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy Surface Brightness Star-counts in outer fields (R > 60 kpc) well above extrapolation of R 1/4 inner spheroid. Best fit: power law R -2.3 halo. Guhathakurta et al. (2006, Nature, submitted) Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy Kalirai et al. (2006, ApJ, submitted) Chemical Composition Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy Kalirai et al. (2006, ApJ, submitted) Chemical Composition Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy Kalirai et al. (2006, ApJ, submitted) Metallicity Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy Kalirai et al. (2006, ApJ, in prep.) Metallicity Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006 Kalirai et al. (2006, ApJ, submitted)

The Metal-Poor Halo of the Andromeda Spiral Galaxy Chemical Composition Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy Conclusions Discovered M31 RGB stars at R = kpc using Keck/DEIMOS. Surface brightness of stars with R > 30 kpc follows an R -2 power law profile: distinct from inner spheroid. Chemical abundance of outer halo is distinct from inner spheroid. R < 20 kpc [Fe/H] =  0.03 (  = 0.39) R ~ 30 kpc [Fe/H] =  0.06 (  = 0.60) R > 60 kpc [Fe/H] =  0.10 (  = 0.72) [Fe/H] spec =  0.12 (  = 0.85) [Fe/H] phot =  0.11 (  = 0.73) [  /Fe] = +0.3 Future observations - improve statistics in halo and characterize shape. M31 Image from GALEX Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

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

The Metal-Poor Halo of the Andromeda Spiral Galaxy Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy M31 Data Sets Deep, Wide-Field Imaging: 1.) CFHT / MegaCam 2.) Kitt Peak / Mosaic DDO51 3.) Subaru / SuprimeCam Faint RGB LF, HB [Fe/H] phot Sub-structure (starcount maps) M31 star-count map (Ferguson et al. 2002) Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy M31 Data Sets Deep, Wide-Field Imaging: 1.) CFHT / MegaCam 2.) Kitt Peak / Mosaic DDO51 3.) Subaru / SuprimeCam Faint RGB LF, HB [Fe/H] phot Sub-structure (starcount maps) M31 star-count map (Ferguson et al. 2002) Kalirai et al. 2006, in prep Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy M31 Data Sets Deep, Wide-Field Imaging: 1.) CFHT / MegaCam 2.) Kitt Peak / Mosaic DDO51 3.) Subaru / SuprimeCam Faint RGB LF, HB [Fe/H] phot Sub-structure (starcount maps) M31 star-count map (Ferguson et al. 2002) Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy M31 Data Sets Ultra-Deep, High Resolution Imaging: 1.) HST / ACS (also WFPC2) Ages HB morphology Brown et al. (2003) Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy Kalirai et al. (2006, ApJ, submitted) Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006

The Metal-Poor Halo of the Andromeda Spiral Galaxy Simulations of Halo Formation Mouhcine et al. (2006) Predictions: 1.) Substructure in halo. Hubble Fellows Symposium, Baltimore MD April. 20 th, 2006