Beyond the Goldilocks Zone: Identifying Critical Features in Massive Black Hole Formation

Abstract

Most galaxies, including the Milky Way, host a supermassive black hole (SMBH) at the center. These SMBHs can be observed out to high redshifts (z>=6) if the accretion rate is sufficiently large. However, we do not fully understand the mechanism through which these black holes form at early times. The heavy (or direct collapse) seeding mechanism has emerged as a probable contender in which the core of an atomic cooling halo directly collapses into a dense stellar cluster that could host supermassive stars that proceed to form a BH seed of mass ~10^5 M_sun. We use the Renaissance simulations to investigate the properties of 35 DCBH candidate host halos at z=15-24 and compare them to non-candidate halos. We aim to understand what features differentiate halos capable of hosting a DCBH from the general halo population with the use of statistical analysis and machine learning methods. We examine 18 halo, central, and environmental properties. We find that DCBH candidacy is more dependent on a halo's core internal properties than on exterior factors such as Lyman-Werner flux and distance to closest galaxy; our analysis selects density and radial mass influx as the most important features (outside candidacy establishing features). Our results concur with the recent suggestion that DCBH host halos neither need to lie within a "Goldilocks zone" nor have a significant amount of Lyman-Werner flux to suppress cooling. This paper presents insight to the dynamics possibly occurring in potential DCBH host halos and seeks to provide guidance to DCBH subgrid formation models.