The star formation histories of local group dwarf galaxies. II. Searching for signatures of reionization

Daniel R. Weisz, Andrew E. Dolphin, Evan D. Skillman, Jon Holtzman, Karoline M. Gilbert, Julianne J. Dalcanton, Benjamin F. Williams

Research output: Contribution to journalArticlepeer-review

138 Scopus citations


We search for signatures of reionization in the star formation histories (SFHs) of 38 Local Group dwarf galaxies (104 < M* < 109 M). The SFHs are derived from color-magnitude diagrams using archival Hubble Space Telescope/Wide Field Planetary Camera 2 imaging. Only five quenched galaxies (And V, And VI, And XIII, Leo IV, and Hercules) are consistent with forming the bulk of their stars before reionization, when full uncertainties are considered. Observations of 13 of the predicted "true fossils" identified by Bovill & Ricotti show that only two (Hercules and Leo IV) indicate star formation quenched by reionization. However, both are within the virial radius of the Milky Way and evidence of tidal disturbance complicates this interpretation. We argue that the late-time gas capture scenario posited by Ricotti for the low mass, gas-rich, and star-forming fossil candidate Leo T is observationally indistinguishable from simple gas retention. Given the ambiguity between environmental effects and reionization, the best reionization fossil candidates are quenched low mass field galaxies (e.g., KKR 25).

Original languageEnglish (US)
Article number148
JournalAstrophysical Journal
Issue number2
StatePublished - Jul 10 2014


  • Local Group
  • dark ages, reionization, first stars
  • galaxies: dwarf
  • galaxies: evolution
  • galaxies: formation
  • galaxies: stellar content


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