Star Formation History of Elliptical Galaxies from Low-Redshift Evidence

Abstract

Star formation in elliptical galaxies (Es) was and is mostly dominated by mergers and accretions with many suggestive examples seen among local galaxies. Present day star formation in Es is easily measurable in two thirds of Es and appears bursty in character. Direct age determinations from integrated light indicate real age scatter. If one assumes the oldest-looking galaxies are a Hubble time old, the light weighted mean ages of the rest spread to 0.5 of a Hubble time, with scatterlings at very young ages. Larger Es and Es in clusters have less age scatter than smaller or field Es. The size trend is clear. The environment trend needs to be rechecked with better data even though it agrees with high redshift field/cluster results.