Hunting the first Cosmic Giants: formation and detectability of Direct Collapse Black Holes around high-redshift quasars

TL;DR

This study models the formation and potential observability of direct collapse black holes in the early Universe, suggesting they could be detected around high-redshift quasars with JWST, shedding light on SMBH origins.

Contribution

It combines semi-analytic models with N-body simulations to predict the formation and survival of DCBHs in early cosmic structures, providing new insights into their detectability.

Findings

DCBHs can form as early as redshift 22 under certain conditions.

Tens of DCBHs are predicted to exist down to redshift 14.

A significant fraction of early DCBHs survive in satellite galaxies until redshift 7.

Abstract

The rapid emergence of supermassive black holes (SMBHs) in the early Universe poses a challenge to current models of black hole growth. One promising formation pathway is the direct collapse black hole (DCBH) scenario, in which gas in pristine, low-metallicity halos forms supermassive (or quasi-) stars leading to massive black holes seeds under specific environmental conditions. In this work, we investigate the potential host environments of DCBHs by coupling a semi-analytic model tracing BH formation and galaxy co-evolution with high-resolution N-body dark matter merger trees. This allows us to trace the population of DCBHs formed during the hierarchical assembly of a $\sim 10^{12} ~\rm M_\odot$ dark matter halo hosting a bright $10^9 ~\rm M_\odot$ quasar at redshift $z \approx 7$. We find that, when accounting for local fluctuations in the UV radiation field within this early cosmic structure, massive BH seeds can form via direct collapse as early as $z \approx 22$. Even under more stringent conditions for heavy seed formation, tens of DCBHs are predicted to emerge within the simulated overdensity down to $z \sim 14$, at which point metal enrichment of the intergalactic medium inhibits further episodes of direct collapse. A significant fraction of the massive black hole population formed at $z > 14$ is expected to survive in satellite galaxies that do not merge with the central halo down to $z \approx 7$. We show that the existence of such a population of ungrown heavy BH seeds can be probed through deep JWST observations targeting regions surrounding bright high-redshift quasars, and we discuss tailored observational strategies to detect and identify these elusive systems.