The Surface Brightness Profile of the Bulge and Halo of the Andromeda Spiral Galaxy (M31) from R = 10 to 165 kiloparsecs

Details The Surface Brightness Profile of the Bulge and Halo of the Andromeda Spiral Galaxy (M31) from R = 10 to 165 kiloparsecs The Surface Brightness Profile of the Bulge and Halo of the Andromeda Spiral Galaxy (M31) from R = 10 to 165 kiloparsecs

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20917701g&link_type=abstract

2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #177.01; Bulletin of the American Astronomical Society,

Astronomy and Astrophysics

Astronomy

Scientific paper

Understanding the formation of galaxies and their structural subcomponents is a key goal of modern cosmology. Large spiral galaxies like our own consist of a flattened rotating disk, a centrally concentrated bulge whose density decreases exponentially with increasing radius, and an extended halo whose density scales as an inverse power law in radius. Our internal vantage point is disadvantageous for investigating the structure of our own Galaxy. By contrast, the Andromeda spiral galaxy (M31), the Milky Ways neighbour, offers us a global external perspective and yet is close enough for individual stars to be resolved. Over several decades, structural studies of M31 have generally concluded that its outer spheroid is an extension of its inner bulge, displaying the characteristic exponential cut-off out to a distance of about 20 kpc from the center, and/or that its halo is undetected or absent. We report here on the discovery of a halo of red giant stars in M31 extending beyond a radius of 150 kpc. Our finding shows that previous studies of the spheroid of M31 spanning the last few decades have been sampling its extended bulge instead of the pristine metal-poor halo. Characterizing the dynamics, metallicity, substructure, and age of M31's halo will provide unique tests of galaxy formation theories.
This research was supported by funds from the NSF and NASA/STScI.

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