The large-scale structure of the halo of the Andromeda Galaxy Part I: global stellar density, morphology and metallicity properties

Дата и время публикации : 2013-11-22T21:00:04Z

Авторы публикации и институты :
Rodrigo A. Ibata
Geraint F. Lewis
Alan W. McConnachie
Nicolas F. Martin
Michael J. Irwin
Annette M. N. Ferguson
Arif Babul
Edouard J. Bernard
Scott C. Chapman
Michelle Collins
Mark Fardal
A. D. Mackey
Julio Navarro
Jorge Penarrubia
R. Michael Rich
Nial Tanvir
Lawrence Widro

Ссылка на журнал-издание: Ссылка на журнал-издание не найдена
Коментарии к cтатье: 21 pages, 17 figures, accepted for publication in the Astrophysical Journal
Первичная категория: astro-ph.GA

Все категории : astro-ph.GA, astro-ph.CO

Краткий обзор статьи: We present an analysis of the large-scale structure of the halo of the Andromeda galaxy, based on the Pan-Andromeda Archeological Survey (PAndAS), currently the most complete map of resolved stellar populations in any galactic halo. Despite copious substructure, the global halo populations follow closely power law profiles that become steeper with increasing metallicity. We divide the sample into stream-like populations and a smooth halo component. Fitting a three-dimensional halo model reveals that the most metal-poor populations ([Fe/H]<-1.7) are distributed approximately spherically (slightly prolate with ellipticity c/a=1.09+/-0.03), with only a relatively small fraction (42%) residing in discernible stream-like structures. The sphericity of the ancient smooth component strongly hints that the dark matter halo is also approximately spherical. More metal-rich populations contain higher fractions of stars in streams (86% for [Fe/H]>-0.6). The space density of the smooth metal-poor component has a global power-law slope of -3.08+/-0.07, and a non-parametric fit shows that the slope remains nearly constant from 30kpc to 300kpc. The total stellar mass in the halo at distances beyond 2 degrees is 1.1×10^10 Solar masses, while that of the smooth component is 3×10^9 Solar masses. Extrapolating into the inner galaxy, the total stellar mass of the smooth halo is plausibly 8×10^9 Solar masses. We detect a substantial metallicity gradient, which declines from [Fe/H]=-0.7 at R=30kpc to [Fe/H]=-1.5 at R=150kpc for the full sample, with the smooth halo being 0.2dex more metal poor than the full sample at each radius. While qualitatively in-line with expectations from cosmological simulations, these observations are of great importance as they provide a prototype template that such simulations must now be able to reproduce in quantitative detail.

Category: Physics