Satellite dwarf galaxies in a hierarchical universe: Infall histories, group preprocessing, and reionization
- TAPIR, California Institute of Technology, Pasadena, CA 91125 (United States)
- Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)
- Center for Cosmology, Department of Physics and Astronomy, University of California, Irvine, CA 92697 (United States)
In the Local Group (LG), almost all satellite dwarf galaxies that are within the virial radius of the Milky Way (MW) and Andromeda (M31) exhibit strong environmental influence. The orbital histories of these satellites provide the key to understanding the role of the MW/M31 halo, lower-mass groups, and cosmic reionization on the evolution of dwarf galaxies. We examine the virial-infall histories of satellites with M{sub star}=10{sup 3−9} M{sub ⊙} using the Exploring the Local Volume in Simulations suite of cosmological zoom-in dissipationless simulations of 48 MW/M31-like halos. Satellites at z = 0 fell into the MW/M31 halos typically 5−8 Gyr ago at z=0.5−1. However, they first fell into any host halo typically 7−10 Gyr ago at z=0.7−1.5. This difference arises because many satellites experienced “group preprocessing” in another host halo, typically of M{sub vir}∼10{sup 10−12} M{sub ⊙}, before falling into the MW/M31 halos. Satellites with lower mass and/or those closer to the MW/M31 fell in earlier and are more likely to have experienced group preprocessing; half of all satellites with M{sub star}<10{sup 6} M{sub ⊙} were preprocessed in a group. Infalling groups also drive most satellite–satellite mergers within the MW/M31 halos. Finally, none of the surviving satellites at z = 0 were within the virial radius of their MW/M31 halo during reionization (z>6), and only <4% were satellites of any other host halo during reionization. Thus, effects of cosmic reionization versus host-halo environment on the formation histories of surviving dwarf galaxies in the LG occurred at distinct epochs, separated typically by 2−4 Gyr, so they are separable theoretically and, in principle, observationally.
- OSTI ID:
- 22882967
- Journal Information:
- Astrophysical Journal, Vol. 807, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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