Impact of radiation backgrounds on the formation of massive black holes

Abstract

The presence of supermassive black holes (SMBHs) of a few billion solar masses at very high redshift has motivated us to study how these massive objects formed during the first billion years after the Big Bang. The most promising model that has been proposed to explain this is the direct collapse of protogalactic gas clouds. In this scenario, very high accretion rates are needed to form massive objects early on and the suppression of $\mathrm H_2$ cooling is important in regulating the fragmentation. Recent studies have shown that if we use a strong radiation background, the hydrogen molecules are destroyed, favoring the high accretion rates and therefore producing objects of very high mass. In this work we study the impact of UV radiation fields in a primordial gas cloud using the recently coupled code GRADSPH-KROME for the modeling of gravitational collapse including primordial chemistry to explore the fragmentation in AU scales and hence the formation of first SMBHs. We found that to suppress the formation of $\mathrm H_2$ a very high value of $J_{21}$ is required, because of that we conclude that the direct collapse black holes (DCBHs) are very unlikely to be an explanation for the formation of the first SMBHs.