The Formation of Quasars in Low‐Luminosity Hosts via Galaxy Harassment

We have simulated disk galaxies undergoing continual bombardment by othergalaxies in a rich cluster. "Galaxy harassment" leads to dramatic evolution ofsmaller disk galaxies and provides an extremely effective mechanism to fuel acentral quasar. Within a few billion years after a small disk galaxy enters thecluster environment, up to 90% of its gas can be driven into the inner 500 pc.Up to half of the mass can be transferred in a burst lasting just 100-200 Myr.This transport of gas to the center of galaxy is far more efficient than anymechanism proposed before. Galaxy harassment was first proposed to explain thedisturbed blue galaxies in clusters seen in clusters at ($z \gsim 0.3$), the"Butcher-Oemler effect". Quasars at the same reshifts lie in more clusteredenvironments than those at lower redshift. Recent HST observations find thatroughly half of all observed quasar host galaxiess are fainter than \l*, withmany of these less luminous hosts occuring at redshifts $z \gsim 0.3$. Weexamine 5 quasars that are claimed to have low luminosity hosts and find that 3are in rich clusters of galaxies, the fourth may be in a cluster but theevidence for this is marginal. The environment of the fifth has not beenstudied.Comment: Final version, to be published in the Ap.J. 1998, video edition with the "Galaxy Harassment" movi