FORGE'd in FIRE III: The IMF in Quasar Accretion Disks from STARFORGE
arxiv(2024)
摘要
Recently, we demonstrated self-consistent formation of strongly-magnetized
quasar accretion disks (QADs) from cosmological
radiation-magnetohydrodynamic-thermochemical galaxy-star formation simulations,
including the full STARFORGE physics shown previously to produce a reasonable
IMF under typical ISM conditions. Here we study star formation and the stellar
IMF in QADs, on scales from 100 au to 10 pc from the SMBH. We show it is
critical to include physics often previously neglected, including magnetic
fields, radiation, and (proto)stellar feedback. Closer to the SMBH, star
formation is suppressed, but the (rare) stars that do form exhibit top-heavy
IMFs. Stars can form only in special locations (e.g. magnetic field switches)
in the outer QAD. Protostars accrete their natal cores rapidly but then
dynamically decouple from the gas and 'wander,' ceasing accretion on timescales
100 yr. Their jets control initial core accretion, but the ejecta are 'swept
up' into the larger-scale QAD flow without much dynamical effect. The strong
tidal environment strongly suppresses common-core multiplicity. The IMF shape
depends sensitively on un-resolved dynamics of protostellar disks (PSDs), as
the global dynamical times can become incredibly short (< yr) and tidal fields
are incredibly strong, so whether PSDs can efficiently transport angular
momentum or fragment catastrophically at <10 au scales requires novel PSD
simulations to properly address. Most analytic IMF models and analogies with
planet formation in PSDs fail qualitatively to explain the simulation IMFs,
though we discuss a couple of viable models.
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