The role of gas fragmentation during the formation of supermassive black holes

Abstract

We have performed cosmological hydrodynamic simulations to study the effect of fragmentation on the SMBH seed mass in the direct collapse formation scenario. We considered different background UV intensities, host halo spin, and halo merger histories. Our simulations in low-spin halos, in the presence of a strong UV background are consistent with the Direct Collapse Black Hole model, in which a single massive object $\sim 10^5$ M${}_{\odot }$ is formed in the center of a proto-galaxy. While in our simulations under the presence of a low UV background, we find fragmentation and the formation of various minor seeds. These fragments have masses of 10${}^3$ - 10${}^4$ M${}_{\odot }$. These values are 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. In one of our simulations, we observed gas fragmentation even in the presence of a strong UV intensity. Said structure arose in a dark matter halo that formed after various merger episodes, and the one with the highest spin value. The final mass obtained was $\sim 10^5$ M${}_{\odot }$ in this run. From these results, we conclude that fragmentation in fact produces less massive objects, however, they are still prone to merge. In simulations that formed many fragments, they all approach the most massive one with time. We see no uniqueness in the strength of the UV intensity value required to achieve a DCBH, since it depends in other factors like the system dynamics in our cases.

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