On the uniqueness of kinematical signatures of intermediate-mass black holes in globular clusters

TL;DR

This paper investigates whether the kinematic signatures used to detect intermediate-mass black holes in globular clusters are unique, highlighting the degeneracy with pressure anisotropy and its implications for IMBH identification.

Contribution

It demonstrates that considering anisotropic models can explain the velocity dispersion profile without requiring an IMBH, challenging previous assumptions about detection signatures.

Findings

Anisotropic models can mimic IMBH signatures in velocity dispersion profiles.

Models without IMBHs do not show a central cusp in velocity dispersion.

Pressure anisotropy can partially explain observed kinematic features.

Abstract

Finding an intermediate-mass black hole (IMBH) in a globular cluster (GC), or proving its absence, is a crucial ingredient in our understanding of galaxy formation and evolution. The challenge is to identify a unique signature of an IMBH that cannot be accounted for by other processes. Observational claims of IMBH detection are often based on analyses of the kinematics of stars, such as a rise in the velocity dispersion profile towards the centre. In this contribution we discuss the degeneracy between this IMBH signal and pressure anisotropy in the GC. We show that that by considering anisotropic models it is possible to partially explain the innermost shape of the projected velocity dispersion profile, even though models that do not account for an IMBH do not exhibit a cusp in the centre.