GALEX Constraints on AGN Feedback in Early-Type Galaxies

The absence of vigorous star formation in early-type galaxies is a mystery because early-type galaxies do have a copious supply of cold gas. Various heating mechanisms have been put forward to explain this, and AGN feedback is one of the most widely suspected culprits. The GALEX UV telescope detects even a small amount of star formation and allows an estimate of the current and recent star formation. We find that star formation is still common in early-type galaxies with low velocity dispersion where the black hole mass is believed to be small. We compare the star-formation rates of the galaxies with predictions from various semi-analytic models with different feedback prescriptions. We find that the passive behavior of central galaxies in groups and clusters is reproduced by semi-analytic models with AGN feedback. However, the same prescriptions causes satellite (i.e., non-central) galaxies to be quenched as well, much more than observed by GALEX, leading to a “satellite over-quenching problem.”