Competitive feedback in galaxy formation

TL;DR

This paper proposes a competitive feedback model between nuclear star clusters and supermassive black holes to explain their different mass correlations with galaxy velocity dispersion, highlighting a mass cutoff mechanism.

Contribution

It introduces a new competitive feedback framework that explains the mass transition between nuclear star clusters and SMBHs in galaxy formation.

Findings

Nuclear star clusters typically have masses below 10^8 Msun.

Supermassive black holes often exceed 10^8 Msun.

The model accounts for the observed mass cutoff and correlation differences.

Abstract

It is now well established that many galaxies have nuclear star clusters (NCs) whose total masses correlate with the velocity dispersion (sigma) of the galaxy spheroid in a very similar way to the well--known supermassive black hole (SMBH) M - sigma relation. Previous theoretical work suggested that both correlations can be explained by a momentum feedback argument. Observations further show that most known NCs have masses < 10^8 Msun, while SMBHs frequently have masses > 10^8 Msun, which remained unexplained in previous work. We suggest here that this changeover reflects a competition between the SMBH and nuclear clusters in the feedback they produce. When one of the massive objects reaches its limiting M-sigma value, it drives the gas away and hence cuts off its own mass and also the mass of the ``competitor''. The latter is then underweight with respect to the expected M-sigma mass (abridged).