The Most Massive Black Holes in Small Galaxies

Massive galaxies represent the extreme of galaxy formation and contain the most massive black holes (BH), as reflected in the scaling relations of BH masses with galaxy velocity dispersions (MÔÇô¤â)┬áand luminosities (MÔÇôL). Our spectroscopic survey of 600 nearby galaxies revealed 17 galaxies with extremely high velocity dispersions (indicating BH masses of 10^10 solar masses) and at the same time shockingly small sizes (<2 kpc) and (bulge) luminosities. For one of these galaxies archival HST imaging allowed us to measure an extremely big BH mass of 23 billion solar masses, and confirm it is hosted by a small disk-dominated galaxy of only 90 billion solar masses in stars. This demonstrates that the BH in this system did not co-evolve with its host galaxy the way others are thought to have. It is imperative to go beyond a single anecdotal example to a real sample of galaxies with small bulges and suspected monster black holes. Here we propose to obtain HST imaging of the other 16 galaxies. The WFC3 imaging is required to resolve their small bulge and put accurate constraints (in combination with our spectroscopy) on their black hole mass. A significant sample of compact galaxies with very high black hole masses would be in stark conflict with the popular co-evolution picture and could form the missing link between local galaxies and the quiescent compact nugget galaxies found at z~2.