paper

The ACS LCID project. V. The Star Formation History of the Dwarf Galaxy \objectname[]{LGS-3}: Clues for Cosmic Reionization and Feedback

arXiv:1101.5762 · doi:10.1088/0004-637X/730/1/14

Abstract

We present an analysis of the star formation history (SFH) of the transition-type (dIrr/dSph) Local Group galaxy \objectname[]{LGS-3} (Pisces) based on deep photometry obtained with the {\it Advanced Camera for Surveys} onboard the {\it Hubble Space Telescope}. Our analysis shows that the SFH of \objectname[]{LGS-3} is dominated by a main episode Gyr ago with a duration of 1.4 Gyr which formed of the stars. Subsequently, \objectname[]{LGS-3} continued forming stars until the present, although at a much lower rate. The lack of early chemical enrichment is in contrast to that observed in the isolated dSph galaxies of comparable luminosity, implying that the dSphs were more massive and subjected to more tidal stripping. We compare the SFH of \objectname[]{LGS-3} with expectations from cosmological models. Most or all the star formation was produced in \objectname[]{LGS-3} after the reionization epoch, assumed to be completed at or Gyr ago. The total mass of the galaxy is estimated to be between 2 and M, corresponding to circular velocities between 28 km\ s to 36 km\ s. These values are close to but somewhat above the limit of 30 km\ s below which the UV background is expected to prevent any star formation after reionization. Feedback from SNe associated with the initial episode of star formation (mechanical luminosity from SNe erg s) is probably inadequate to completely blow away the gas. However, the combined effects of SN feedback and UV background heating might be expected to completely halt star formation at the reionization epoch for the low mass of \objectname[]{LGS-3}; this suggests that self-shielding is important to the early evolution of galaxies in this mass range.

accepted to be published at ApJ

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