Kavli Affiliate: Debora Sijacki
| First 5 Authors: Eun-jin Shin, Debora Sijacki, Matthew C. Smith, Martin A. Bourne, Sophie Koudmani
| Summary:
While mounting observational evidence suggests that intermediate mass black
holes (IMBHs) may be important in shaping the properties of dwarf galaxies both
at high redshifts and in the local Universe, our theoretical understanding of
how these IMBHs grow is largely incomplete. To address this, we perform
high-resolution simulations of an isolated dwarf galaxy with a virial mass of
$10^{10}~{rm M}_{odot}$ harbouring a $10^4~{rm M}_{odot}$ IMBH at its
centre at a peak spatial resolution of $lesssim 0.01$ pc. Within the fully
multi-phase interstellar medium (ISM), we incorporate explicit sampling of
stars from the initial mass function, photo-ionization, photoelectric heating,
individual supernovae (SNe), as well as a Shakura-Sunyaev accretion disc model
to track the evolution of BH mass and spin. We find that a nuclear star cluster
(NSC) effectively captures the ISM gas and promotes formation of a
circumnuclear disc (CND) on scales of $lesssim 7$ pc. Simultaneously,
gravitational torques from the NSC reduce CND angular momentum on (sub-)parsec
scales, circularizing the gas onto the $alpha$-accretion disc and promoting
sustained IMBH growth at $sim 0.01$ of the Eddington rate. While in the
innermost regions ($lesssim 0.5$ pc), star formation is highly suppressed, the
CND is susceptible to fragmentation, leading to the formation of massive, young
stars. Interestingly, despite an in-situ SN rate of $0.3~{rm Myr}^{-1}$, the
dense CND persists, sustaining BH accretion and leading to its net spin-up. Our
study demonstrates the complexity of IMBH accretion within a multi-phase ISM,
and paves the way for next-generation studies where IMBH growth in a fully
cosmological context can be captured.
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