Misc,
Black hole formation and growth with non-Gaussian primordial density perturbations
(2015)cite arxiv:1507.05971Comment: 11 pages, 10 figures, submitted to MNRAS.
Abstract
Quasars powered by massive black holes (BHs) with mass estimates above a
billion solar masses have been identified at redshift 6 and beyond. The
existence of such BHs requires almost continuous growth at the Eddington limit
for their whole lifetime, of order of one billion years. In this paper, we
explore the possibility that positively skewed scale-dependent non-Gaussian
primordial fluctuations may ease the assembly of massive BHs. In particular,
they produce more low-mass halos at high redshift, thus altering the production
of metals and ultra-violet flux, believed to be important factors in BH
formation. Additionally, a higher number of progenitors and of nearly
equal-mass halo mergers would boost the mass increase provided by BH-BH mergers
and merger-driven accretion. We use a set of two cosmological simulations, with
either Gaussian or scale-dependent non-Gaussian primordial fluctuations to
perform a proof-of-concept experiment to estimate how BH formation and growth
are altered. We estimate the BH number density and the fraction of halos where
BHs form, for both simulations and for two popular scenarios of BH formation
(remnants of the first generation of stars and direct collapse in the absence
of metals and molecular hydrogen). We find that the fractions of halos where
BHs form are almost identical, but that non-Gaussian primordial perturbations
increase the total number density of BHs for the both BH formation scenarios.
We also evolve BHs using merger trees extracted from the simulations and find
that non-Gaussianities increase both the BH masses and the number of the most
massive BHs.
