TY - JOUR
T1 - The star formation histories of local group dwarf galaxies. II. Searching for signatures of reionization
AU - Weisz, Daniel R.
AU - Dolphin, Andrew E.
AU - Skillman, Evan D.
AU - Holtzman, Jon
AU - Gilbert, Karoline M.
AU - Dalcanton, Julianne J.
AU - Williams, Benjamin F.
PY - 2014/7/10
Y1 - 2014/7/10
N2 - 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).
AB - 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).
KW - Local Group
KW - dark ages, reionization, first stars
KW - galaxies: dwarf
KW - galaxies: evolution
KW - galaxies: formation
KW - galaxies: stellar content
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U2 - 10.1088/0004-637X/789/2/148
DO - 10.1088/0004-637X/789/2/148
M3 - Article
AN - SCOPUS:84903271747
SN - 0004-637X
VL - 789
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 148
ER -