Extrapolating SMBH correlations down the mass scale: the case for IMBHs in globular clusters

Abstract

Empirical evidence for both stellar mass black holes (M (aEuro cent)< 10(2) M (aS (TM))) and supermassive black holes (SMBHs, M (aEuro cent)> 10(5) M (aS (TM))) is well established. Moreover, every galaxy with a bulge appears to host a SMBH, whose mass is correlated with the bulge mass, and even more strongly with the central stellar velocity dispersion sigma (c) , the M (aEuro cent)-sigma relation. On the other hand, evidence for "intermediate-mass" black holes (IMBHs, with masses in the range 100-10(5) M (aS (TM))) is relatively sparse, with only a few mass measurements reported in globular clusters (GCs), dwarf galaxies and low-mass AGNs. We explore the question of whether globular clusters extend the M (aEuro cent)-sigma relationship for galaxies to lower black hole masses and find that available data for globular clusters are consistent with the extrapolation of this relationship. We use this extrapolated M (aEuro cent)-sigma relationship to predict the putative black hole masses of those globular clusters where existence of central IMBH was proposed. We discuss how globular clusters can be used as a constraint on theories making specific predictions for the low-mass end of the M (aEuro cent)-sigma relation.