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25 April 2024 |
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The Extended Star Formation History of the Andromeda Spheroid at 35 Kpc on the Minor Axis | | Thomas M. Brown
; Rachael Beaton
; Masashi Chiba
; Henry C. Ferguson
; Karoline M. Gilbert
; Puragra Guhathakurta
; Masanori Iye
; Jasonjot S. Kalirai
; Andreas Koch
; Yutaka Komiyama
; Steven R. Majewski
; David B. Reitzel
; Alvio Renzini
; R. Michael Rich
; Ed Smith
; Allen V. Sweigart
; Mikito Tanaka
; | | Date: |
19 Aug 2008 | | Abstract: | Using the HST ACS, we have obtained deep optical images reaching well below
the oldest main sequence turnoff in fields on the southeast minor-axis of the
Andromeda Galaxy, 35 kpc from the nucleus. These data probe the star formation
history in the extended halo of Andromeda -- that region beyond 30 kpc that
appears both chemically and morphologically distinct from the metal-rich,
highly-disturbed inner spheroid. The present data, together with our previous
data for fields at 11 and 21 kpc, do not show a simple trend toward older ages
and lower metallicities, as one might expect for populations further removed
from the obvious disturbances of the inner spheroid. Specifically, the mean
ages and [Fe/H] values at 11 kpc, 21 kpc, and 35 kpc are 9.7 Gyr and -0.65,
11.0 Gyr and -0.87, and 10.5 Gyr and -0.98, respectively. In the best-fit model
of the 35 kpc population, one third of the stars are younger than 10 Gyr, while
only ~10% of the stars are truly ancient and metal-poor. The extended halo thus
exhibits clear evidence of its hierarchical assembly, and the contribution from
any classical halo formed via early monolithic collapse must be small. | | Source: | arXiv, 0808.2648 | | Services: | Forum | Review | PDF | Favorites | |
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