Kavli Affiliate: Mark Vogelsberger
| First 5 Authors: Jonathan Kho, Jonathan Kho, , ,
| Summary:
The James Webb Space Telescope (JWST) has identified a large population of
supermassive ($10^6$-$10^8~mathrmM_odot$) black holes (BHs) in the early
universe ($z sim 4$-$7$). Current measurements suggest that many of these BHs
exhibit higher BH-to-stellar mass ratios than local populations, opening a new
window into the earliest stages of BH-galaxy coevolution and offering the
potential to place tight constraints on BH seeding and growth in the early
universe. In this work, we use the BRAHMA simulations to investigate the impact
of BH seeding on the $mathrmM_bullet-sigma$ relation. These simulations
adopt heavy $sim10^5~mathrmM_odot$ seeds and systematically varied BH
seeding models, resulting in distinct predictions for seed abundances. We find
that different seed models lead to different normalizations of the
$mathrmM_bullet-sigma$ relation at higher redshifts ($z > 2$) across all
$sigma$, and at low redshift for systems with low $sigma$ ($50~mathrmkm
s^-1 lesssim sigma lesssim 80~mathrmkm s^-1$). The most lenient
seed model also shows negligible evolution in the $mathrmM_bullet-sigma$
relation across redshift, while more restrictive models have substantially
lower normalization on the $mathrmM_bullet-sigma$ relation for high
$sigma$ ($sim 100~mathrmkm s^-1$) at high redshifts, and evolve upward
toward the local relation. We demonstrate that the
$mathrmM_bullet-sigma$ evolution is a direct consequence of
merger-dominated BH growth in low mass galaxies ($lesssim 10^9~M_odot$) and
accretion dominated BH growth in high mass ($gtrsim10^9~M_odot$) galaxies.
Furthermore, the scatter in the $mathrmM_bullet-sigma$ relation is
larger for the more restrictive models due to the inability of many BHs to grow
significantly beyond their seed mass.
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