An HST/ACS View of the Inhomogeneous Outer Halo of M31
Date
2009-03-19Author
Richardson, J. C.
Ferguson, A. M. N.
Mackey, A. D.
Irwin, M. J.
Chapman, S. C.
Huxor, A.
Ibata, R. A.
Lewis, G. F.
Tanvir, N. R.
Metadata
Show full item recordAbstract
We present a high precision photometric view of the stellar populations in the outer halo of M31, using data taken with the Hubble Space Telescope Advanced Camera for Surveys (HST/ACS). We analyse the field populations adjacent to 11 luminous globular clusters which sample the galactocentric radial range 18 = -0.6 to -1.0 dex and considerable metallicity dispersions of 0.2 to 0.3 dex (assuming a 10 Gyr population and scaled-Solar abundances). The average metallicity over the range 30 - 60 kpc is [Fe/H] = -0.8 +/- 0.14 dex, with no evidence for a significant radial gradient. Metal-poor stars ([Fe/H] <= -1.3) typically account for < 10-20 % of the population in each field, irrespective of radius. Assuming our fields are unbiased probes of the dominant stellar populations in these parts, we find that the M31 outer halo remains considerably more metal-rich than that of the Milky Way out to at least 60 kpc.
Citation
Richardson, J. C., A. M. N. Ferguson, A. D. Mackey, M. J. Irwin, et al. 2009. "An HST/ACS View of the Inhomogeneous Outer Halo of M31." Monthly Notices of the Royal Astronomical Society 396:1842.