Supermassive Black Holes in Bulgeless and Low Mass Galaxies

spitzer20080110-hiresWe now know that supermassive black holes (SMBHs) one million to a few billion times the mass of the sun lurk in the centers of possibly all bulge-dominated galaxies in the local Universe and that their mass is strongly correlated with the galaxy’s bulge mass. These observations have formed the basis of the widely held view that galaxies and their central black holes are fundamentally linked: a link that can most simply be understood if galaxy mergers induce bulge growth and feed the central black hole in concert. While the SMBH and host galaxy properties in the high bulge mass regime have been studied extensively, very little is known about the existence and properties of SMBHs in galaxies with low masses and those with small bulges. This is a significant deficiency since the study of this population allows us to gain an understanding of merger-free pathways to black hole growth. Furthermore, the occupation fraction and properties of SMBHs in galaxies with low masses and in those with no evidence for a bulge provide one of the only observational constraints on the origin and growth efficiency of SMBH seeds, thought to have formed at high redshift. Since SMBHs in massive bulge-dominated galaxies have undergone significant accretion through multiple dynamical interactions over cosmic history, any information on the seed population will not be retained. In contrast, galaxies that lack significant bulges have undergone a more secular evolution and therefore the mass distribution and occupation fraction of SMBHs in these galaxies contains clues about the original seed population, allowing us to discriminate between lower mass seeds formed from stellar remnants or massive seeds formed directly out of dense gas . The study of black holes at the low bulge mass regime is therefore crucial to our understanding of both the origin of SMBHs and their growth and connection to galaxy evolution.

Our group has been carrying out a multi wavelength investigation of bulgeless and low mass galaxies in order to search for and characterize the properties of their SMBHs. The goals of our research are to:

1. Determine the fraction of bulgeless galaxies that host AGNs

2. Determine if the incidence of AGN activity is correlated in any way with the host galaxy’s properties in the absence of a bulge

3. Study the connection between the black hole properties and those of the host galaxies in bulgeless galaxies.

Faculty associated with this research project: Dr. Shobita Satyapal and Dr. Mario Gliozzi