Journal
ASTROPHYSICAL JOURNAL LETTERS
Volume 790, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/2041-8205/790/2/L17
Keywords
dark matter; galaxies: dwarf; galaxies: halos; galaxies: star formation; galaxies: stellar content
Categories
Funding
- NSF [OIA-112445329745]
- NASA [NNX12AF87G]
- NASA through Hubble Fellowship [HST-HF-51331.01]
- STScI
- Direct For Mathematical & Physical Scien [1229745] Funding Source: National Science Foundation
- Division Of Astronomical Sciences [1229745] Funding Source: National Science Foundation
- Office Of The Director
- Office of Integrative Activities [1124453] Funding Source: National Science Foundation
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On dwarf galaxy scales, the different shapes of the galaxy stellar mass function and the dark halo mass function require a star-formation efficiency (SFE) in these systems that is currently more than 1 dex lower than that of Milky Way-size halos. Here, we argue that this trend may actually be reversed at high redshift. Specifically, by combining the resolved star-formation histories of nearby isolated dwarfs with the simulated mass-growth rates of dark matter halos, we show that the assembly of these systems occurs in two phases: (1) an early, fast halo accretion phase with a rapidly deepening potential well, characterized by a high SFE; and (2) a late, slow halo accretion phase where, perhaps as a consequence of reionization, the SFE is low. Nearby dwarfs have more old stars than predicted by assuming a constant or decreasing SFE with redshift, a behavior that appears to deviate qualitatively from the trends seen among more massive systems. Taken at face value, the data suggest that at sufficiently early epochs, dwarf galaxy halos above the atomic cooling mass limit can be among the most efficient sites of star formation in the universe.
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