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

TL;DR

This paper investigates whether the established galaxy M-sigma relation extends to globular clusters, suggesting they may host intermediate-mass black holes and providing insights into black hole formation at lower mass scales.

Contribution

It demonstrates that the galaxy M-sigma relation can be extrapolated to globular clusters, supporting the potential presence of IMBHs in these systems.

Findings

Globular cluster data align with the extrapolated M-sigma relation.

Predicted black hole masses in globular clusters support the IMBH hypothesis.

Globular clusters can constrain theories of low-mass black hole formation.

Abstract

Empirical evidence for both stellar mass black holes M_bh<10^2 M_sun) and supermassive black holes (SMBHs, M_bh>10^5 M_sun) 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-sigma' relation. On the other hand, evidence for "intermediate-mass" black holes (IMBHs, with masses in the range 1^2 - 10^5 M_sun) 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-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-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-sigma relation.