Evolution of Field Dwarf Galaxies with GEMS
  We present a study of the evolution of late-type field dwarfs over the last ~ 1.9 Gyr, based on HST ACS observations carried out as part of the GEMS survey. This study is amongst the first to probe the evolution of dwarfs over such a large timescale. The comparison of structural properties, particularly size and scale length, indicates that the dwarfs in the redshift range z ~ 0.01 to 0.15 (look-back times up to 1.9 Gyr) are more extended than local dwarfs. We argue that this difference is due to the star formation activity becoming more centrally concentrated in late-type dwarfs over the last ~ 1.9 Gyr. We discuss several possible causes for this evolution. We also find a lack of blue compact dwarfs in the GEMS sample and interpret this as indicative of the fact that strong, centrally concentrated star formation is a feature of evolved dwarfs that are entering their final stages of evolution. 
Fabio D. Barazza (STScI), Shardha Jogee (University of Texas)