Co-Evolution vs. Co-existence: The Effect of Accretion Modelling on the Evolution of Black Holes and Host Galaxies

TL;DR

This study investigates how different black hole accretion models influence the co-evolution of black holes and host galaxies, revealing that accretion modeling significantly impacts their evolutionary relationship and the emergence of scaling relations.

Contribution

It introduces viscous disc and gravitational torque-driven accretion models into galaxy simulations, showing these models naturally produce co-existence without feedback, unlike traditional Bondi-Hoyle accretion.

Findings

Co-existence arises naturally with new accretion models.

Bondi-Hoyle accretion shows a two-step growth pattern.

Feedback controls final masses but isn't the main driver of co-evolution.

Abstract

We append two additional black hole (BH) accretion models, namely viscous disc and gravitational torque-driven accretion, into the Numerical Investigation of a Hundred Astrophysical Objects (NIHAO) project of galaxy simulations. We show that these accretion models, characterized by a weaker dependence on the BH mass compared to the commonly used Bondi-Hoyle accretion, naturally create a common evolutionary track (co-existence) between the mass of the BH and the stellar mass of the galaxy, even without any direct coupling via feedback (FB). While FB is indeed required to control the final BH and stellar mass of the galaxies, our results suggest that FB might not be the leading driver of the cosmic co-evolution between these two quantities; in these models, co-evolution is simply determined by the shared central gas supply. Conversely, simulations using Bondi-Hoyle accretion show a two-step evolution, with an early growth of stellar mass followed by exponential growth of the central supermassive black hole (SMBH). Our results show that the modelling of BH accretion (sometimes overlooked) is an extremely important part of BH evolution and can improve our understanding of how scaling relations emerge and evolve, and whether SMBH and stellar mass co-exist or co-evolve through cosmic time.