The SLUGGS survey: Probing the supermassive black hole connection with bulges and haloes using red and blue globular cluster systems

TL;DR

This study investigates the relationship between supermassive black hole masses and globular cluster system velocity dispersions to understand whether bulges or halos primarily influence black hole growth, using an improved galaxy sample and color-based GC analysis.

Contribution

It provides an updated analysis of the M_BH - sigma_GC relation, exploring color-based GC differences and the impact of radial velocity dispersion gradients, with new predictions for additional galaxies.

Findings

M_BH correlates with total GC system velocity dispersion, but less strongly than previous studies suggested.

No significant difference in the M_BH - sigma_GC relation between barred and non-barred or core and non-core galaxies.

Hints that red GC velocity dispersion may better correlate with M_BH, but data is inconclusive due to low statistics.

Abstract

Understanding whether the bulge or the halo provides the primary link to the growth of supermassive black holes has strong implications for galaxy evolution and supermassive black hole formation itself. In this paper, we approach this issue by investigating extragalactic globular cluster (GC) systems, which can be used to probe the physics of both the bulge and the halo of the host galaxy. We study the relation between the supermassive black hole masses M_BH and the globular cluster system velocity dispersions sigma_GC using an updated and improved sample of 21 galaxies. We exploit the dichotomy of globular cluster system colours, to test if the blue and red globular clusters correlate differently with black hole mass. This may be expected if they trace the potentially different formation history of the halo and of the bulge of the host galaxy respectively. We find that M_BH correlates with the total GC system velocity dispersion, although not as strongly as claimed by recent work of Sadoun & Colin. We also examine the M_BH - sigma_GC relation for barred/bar-less and core/non-core galaxies, finding no significant difference, and for the first time we quantify the impact of radial gradients in the GC system velocity dispersion profile on the M_BH - sigma_GC relation. We additionally predict M_BH in 13 galaxies, including dwarf elliptical galaxies and the cD galaxy NGC 3311. We conclude that our current results cannot discriminate between the bulge/halo scenario. Although there is a hint that the red GC velocity dispersion might correlate better with M_BH than the blue GC velocity dispersion, the number statistics are still too low to be certain.