%0 Generic %1 weisz2014formation %A Weisz, Daniel R. %A Dolphin, Andrew E. %A Skillman, Evan D. %A Holtzman, Jon %A Gilbert, Karoline M. %A Dalcanton, Julianne J. %A Williams, Benjamin F. %D 2014 %K dwarf formation galaxy group histories local star %T The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations %U http://arxiv.org/abs/1404.7144 %X We present uniformly measured star formation histories (SFHs) of 40 Local Group dwarf galaxies based on color-magnitude diagram (CMD) analysis from archival Hubble Space Telescope imaging. We demonstrate that accurate SFHs can be recovered from CMDs that do not reach the oldest main sequence turn-off (MSTO), but emphasize that the oldest MSTO is critical for precisely constraining the earliest epochs of star formation. We find that: (1) the average lifetime SFHs of dwarf spheroidals (dSphs) can be approximated by an exponentially declining SFH with $\tau$ $\sim$ 5 Gyr; (2) lower luminosity dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the average SFHs of dwarf irregulars (dIrrs), transition dwarfs (dTrans), and dwarf ellipticals (dEs) can be approximated by the combination of an exponentially declining SFH ($\tau$ $\sim$ 3-4 Gyr) for lookback ages $>$ 10-12 Gyr ago and a constant SFH thereafter; (4) the observed fraction of stellar mass formed prior to z=2 ranges considerably (80\% for galaxies with M $<$ 10$^5$ M$_ødot$ to 30\% for galaxies with M$>$10$^7$ M$_ødot$) and is largely explained by environment; (5) the distinction between ültra-faint" and "classical" dSphs is arbitrary; (6) LG dIrrs formed a significantly higher fraction of stellar mass prior to z=2 than the SDSS galaxies from Leiter 2012 and the SFHs from the abundance matching models of Behroozi et al. 2013. This may indicate higher than expected star-formation efficiencies at early times in low mass galaxies. Finally, we provide all the SFHs in tabulated electronic format for use by the community.

@misc{weisz2014formation, abstract = {We present uniformly measured star formation histories (SFHs) of 40 Local Group dwarf galaxies based on color-magnitude diagram (CMD) analysis from archival Hubble Space Telescope imaging. We demonstrate that accurate SFHs can be recovered from CMDs that do not reach the oldest main sequence turn-off (MSTO), but emphasize that the oldest MSTO is critical for precisely constraining the earliest epochs of star formation. We find that: (1) the average lifetime SFHs of dwarf spheroidals (dSphs) can be approximated by an exponentially declining SFH with $\tau$ $\sim$ 5 Gyr; (2) lower luminosity dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the average SFHs of dwarf irregulars (dIrrs), transition dwarfs (dTrans), and dwarf ellipticals (dEs) can be approximated by the combination of an exponentially declining SFH ($\tau$ $\sim$ 3-4 Gyr) for lookback ages $>$ 10-12 Gyr ago and a constant SFH thereafter; (4) the observed fraction of stellar mass formed prior to z=2 ranges considerably (80\% for galaxies with M $<$ 10$^5$ M$_{\odot}$ to 30\% for galaxies with M$>$10$^7$ M$_{\odot}$) and is largely explained by environment; (5) the distinction between "ultra-faint" and "classical" dSphs is arbitrary; (6) LG dIrrs formed a significantly higher fraction of stellar mass prior to z=2 than the SDSS galaxies from Leiter 2012 and the SFHs from the abundance matching models of Behroozi et al. 2013. This may indicate higher than expected star-formation efficiencies at early times in low mass galaxies. Finally, we provide all the SFHs in tabulated electronic format for use by the community.}, added-at = {2014-04-30T07:58:52.000+0200}, author = {Weisz, Daniel R. and Dolphin, Andrew E. and Skillman, Evan D. and Holtzman, Jon and Gilbert, Karoline M. and Dalcanton, Julianne J. and Williams, Benjamin F.}, biburl = {https://www.bibsonomy.org/bibtex/2be8d6c4dd2e2361d8c17e2e24c076f9c/miki}, description = {[1404.7144] The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations}, interhash = {3ba5d89dc749c8ff76d7d069f04a41ef}, intrahash = {be8d6c4dd2e2361d8c17e2e24c076f9c}, keywords = {dwarf formation galaxy group histories local star}, note = {cite arxiv:1404.7144Comment: 26 pages, 13 figures. Accepted for publication in ApJS. All photometric data and star formation histories are electronically available from the following websites: http://astronomy.nmsu.edu/logphot (photometry) and http://people.ucsc.edu/~drweisz (star formation histories)}, timestamp = {2014-04-30T07:58:52.000+0200}, title = {The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations}, url = {http://arxiv.org/abs/1404.7144}, year = 2014 }