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26 April 2024 |
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Discovery of an Extended Halo of Metal-poor Stars in the Andromeda Spiral Galaxy | | Puragra Guhathakurta
; James C. Ostheimer
; Karoline M. Gilbert
; R. Michael Rich
; Steven R. Majewski
; Jasonjot S. Kalirai
; David B. Reitzel
; Michael C. Cooper
; Richard J. Patterson
; | | Date: |
8 May 2006 | | Abstract: | We report here on the discovery of an extended halo of metal-poor red giant branch (RGB) stars in the Andromeda spiral galaxy (M31). Our ongoing survey of M31 includes wide-field deep optical images in the intermediate-width DDO51 band and Washington system M and T_2 bands obtained with the Kitt Peak National Observatory 4-m telescope and Mosaic camera. The DDO51 band allows us to screen M31 RGB star candidates from foreground Galactic dwarf star contaminants. The imaging is followed up with spectroscopy using the Keck II 10-m telescope and DEIMOS. A combination of photometric and spectroscopic diagnostics is used to reliably isolate M31 RGB stars; these stars are seen in all of our fields out to a projected distance of 165 kpc from M31’s center. These newly discovered RGB stars represent the hitherto elusive stellar halo of M31. The surface brightness of M31 beyond r > 30 kpc is characterized by a power law, r^{-2.6 +/- 0.3}, distinct from the Se’rsic profile that characterizes its extended bulge. Our data show that M31 is 3-5 times larger than any of its previously mapped spheroidal/disk components. Together, the Galactic and M31 halos span > 1/3 of the distance between them, suggesting that stars occupy a substantial volume fraction of our Local Group, and possibly most galaxy groups. | | Source: | arXiv, astro-ph/0605172 | | Services: | Forum | Review | PDF | Favorites | |
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