Detection of Ongoing, Low-Level Star Formation in Nearby Ellipticals

Small amounts of star formation in early-type galaxies are suggested by several results: surprisingly young ages from optical line index dating, cooling X-ray gas, and mid-IR dust emission. Low levels of star formation have previously been difficult to detect, but using UV imaging from the Hubble Space Telescope's Wide Field Camera 3 (WFC3), we have identified individual young stars and star clusters in four nearby ellipticals by their UV colors and magnitudes. Ongoing, low-level star formation is detected in all four galaxies, including three ellipticals that have previously exhibited potential signposts of star forming conditions (NGC 4636, NGC 4697, and NGC 4374), and our "control” galaxy, the typical "red and dead" elliptical NGC 3379. The detected current star formation rates in our closest targets, where the census of young stars and clusters is reasonably complete, are between 3E-5 and 8E-5 M⊙/yr.