Zooming in on supermassive black holes: how resolving their gas cloud
host renders their accretion episodic
Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2018)
Authors:
Ricarda S Beckmann, Julien Devriendt, Adrianne Slyz
Abstract:
Born in rapidly evolving mini-halos during the first billion years of the
Universe, super- massive black holes (SMBH) feed from gas flows spanning many
orders of magnitude, from the cosmic web in which they are embedded to their
event horizon. As such, accretion onto SMBHs constitutes a formidable challenge
to tackle numerically, and currently requires the use of sub-grid models to
handle the flow on small, unresolved scales. In this paper, we study the impact
of resolution on the accretion pattern of SMBHs initially inserted at the heart
of dense galactic gas clouds, using a custom super-Lagrangian refinement scheme
to resolve the black hole (BH) gravitational zone of influence. We find that
once the self-gravitating gas cloud host is sufficiently well re- solved,
accretion onto the BH is driven by the cloud internal structure, independently
of the BH seed mass, provided dynamical friction is present during the early
stages of cloud collapse. For a pristine gas mix of hydrogen and helium, a slim
disc develops around the BH on sub-parsec scales, turning the otherwise chaotic
BH accretion duty cycle into an episodic one, with potentially important
consequences for BH feedback. In the presence of such a nuclear disc, BH mass
growth predominantly occurs when infalling dense clumps trigger disc
instabilities, fuelling intense albeit short-lived gas accretion episodes.
