부산대학교 도서관

We report preliminary results of a project to homogeneously measure star formation histories for the majority of Local Group dwarf galaxies, based on archival WFPC2 observations. For the dwarf spheroidal and elliptical galaxies, we find that the more luminous systems all show extended star formation episodes, while the less luminous systems typically formed most of their stars over ten Gyr ago. Irregular galaxies show no comparable trend. We find that a galaxy's classification as an irregular or spheroidal is entirely explained by its star formation within the past Gyr or less. Several elliptical/spheroidal systems actively formed stars within the past two Gyr, and would have been indistinguishable from present-day irregulars if observed two Gyr ago.
Comment: 30 pages; Invited Review at the meeting "Resolved Stellar Populations", held in Cancun, Mexico, 18-22 April 2005; paper with full resolution figures available at http://purcell.as.arizona.edu/pubs/cancun.ps.gz