Kavli Affiliate: Mark Vogelsberger
| First 5 Authors: Aklant K. Bhowmick, Laura Blecha, Paul Torrey, Luke Zoltan Kelley, Rainer Weinberger
| Summary:
The first "seeds" of supermassive black holes (BH) can range from
$sim10^2-10^6~M_{odot}$. However, the lowest mass seeds ($lesssim10^3
M_{odot}$) are inaccessible to most cosmological simulations due to resolution
limitations. We present our new BRAHMA suite of cosmological simulations that
uses a novel flexible seeding approach to represent low mass seeds. Our suite
consists of two types of boxes that model $sim10^3~M_{odot}$ seeds using two
distinct but mutually consistent seeding prescriptions at different simulation
resolutions. First, we have the highest resolution $[9~mathrm{Mpc}]^3$
(BRAHMA-9-D3) boxes that directly resolve $sim10^3~M_{odot}$ seeds and place
them within halos with dense and metal poor gas. Second, we have
lower-resolution and larger-volume $[18~mathrm{Mpc}]^3$ (BRAHMA-18-E4) and
$sim[36~mathrm{Mpc}]^3$ (BRAHMA-36-E5) boxes that seed their smallest
resolvable $sim10^4~&~10^5~mathrm{M_{odot}}$ BH descendants using new
stochastic seeding prescriptions calibrated using the BRAHMA-9-D3 results. The
three boxes together probe BHs between $sim10^3-10^7 M_{odot}$ at $z>7$ and
we predict their key observables. The variation in the AGN luminosity functions
is small (factors of $sim2-3$) at the anticipated detection limits of
potential future X-ray facilities ($sim10^{43} mathrm{ergs~s^{-1}}$ at
$zsim7$). Our simulations predict BHs $sim10-100$ times heavier than
expectations from local $M_*$ vs $M_{bh}$ relations, consistent with several
JWST-detected AGN. For different seed models, our simulations merge BH binaries
at $sim1-15~mathrm{kpc}$, with rates of $sim200-2000$ per year for
$gtrsim10^3 M_{odot}$ BHs, $sim6-60$ per year for $gtrsim10^4~M_{odot}$
BHs, and up to $sim10$ per year amongst $gtrsim10^5 M_{odot}$ BHs. These
results suggest that the LISA mission has promising prospects for constraining
seed models.
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