The Role of Gas Fragmentation During the Formation of Supermassive Black Holes

Abstract

Abstract We perform cosmological hydrodynamic simulations to study the effect of gas fragmentation on the formation of supermassive black hole seeds in the context of Direct Collapse. Our setup considers different UV background intensities, host halo spins, and halo merger histories. We observe that our low-spin halos are consistent with the Direct Collapse model when they are irradiated by a UV background of J 21 = 10,000. In these cases, a single massive object ∼105 M ⊙ is formed in the center of the halo. On the other hand, in our simulations irradiated by a UV background of J 21 = 10, we see fragmentation and the formation of various less massive seeds. These fragments have masses of 103–104 M ⊙. These values are still significant if we consider the potential mergers between them and the fact that these minor objects are formed earlier in cosmic time compared to the massive single seeds. Moreover, in one of our simulations, we observe gas fragmentation even in the presence of a strong UV intensity. This structure arises in a dark matter halo that forms after various merger episodes, becoming the structure with the highest spin value. The final black hole seed mass is ∼105 M ⊙ for this run. From these results, we conclude that fragmentation produces less massive objects; however, they are still prone to merge. In simulations that form many fragments, they all approach the most massive one as the simulations evolve. We see no uniqueness in the strength of the UV intensity value required to form a DCBH since it depends on other factors like the system dynamics in our cases.