"SPECIAL SEMINAR: Ongoing star formation in red sequence early-type galaxies - the UV perspective"

ABSTRACT:

"Ongoing star formation in red sequence early-type galaxies - the UV perspective"

Early-type galaxies are generally considered to be old and passive systems, having no current star formation (SF). In this talk I show how UV observations have revealed that a significant fraction of field galaxies on the red sequence exhibit moderate levels of galaxy-scale SF, up to a solar mass per year. What is the origin of the gas that gives rise to SF? Is the SF episodic, related to merging events, or continuous? Our HST and ground-based observations of a sample of low redshift UV-excess early types shows that the extended SF is only found in galaxies with old disks (S0s), but not in true ellipticals, regardless of the galaxy mass. The dichotomy suggests that SF quenching may have different effectiveness in the two Hubble types. Regular morphology of young stars in our sample is indicative of long-lived low-level accretion of gas from the IGM. Minor gas-rich mergers do not appear to be the dominant drivers of SF in early types. These new observations point towards a picture in which significant fraction of field S0s continue to grow their outer disks, while ellipticals remain truly passive.

 

---