# Slowing down of cosmic growth of supermassive black holes: Theoretical prediction of the Eddington ratio distribution

## TL;DR

This paper uses a semi-analytic model to study the evolution of supermassive black holes' growth rates across cosmic time, revealing a decline in high Eddington ratio activity from high to low redshift.

## Contribution

It provides a theoretical prediction of the Eddington ratio distribution of supermassive black holes over a wide redshift range, highlighting the slowdown in their cosmic growth.

## Key findings

- High redshift black holes more likely to exceed Eddington limit
- Super-Eddington growth more common in less massive black holes
- Sample selection affects observed Eddington ratio distributions

## Abstract

We show the Eddington ratio distributions of supermassive black holes at a wide redshift range (0 < z < 8) obtained with a semi-analytic model of galaxy formation. The distribution is broadly consistent with observational estimates at low redshift. We find that the growth rate of black holes at higher redshift is more likely to exceed the Eddington limit because the typical gas fraction of the host galaxies is higher at higher redshift. We also find that the super- Eddington growth is more common for less massive supermassive black holes, supporting an idea that supermassive black holes have been formed via super-Eddington accretion. These results indicate the "slowing down" of cosmic growth of supermassive black holes: the growth of supermassive black holes with a higher Eddington ratio peaks at higher redshift. We also show the effect of the sample selection on the shape of the Eddington ratio distribution functions and find that shallower observations will miss active galactic nuclei with not only the smaller but also higher Eddington ratios.