Kavli Affiliate: Kohei Inayoshi
| First 5 Authors: Kohei Inayoshi, , , ,
| Summary:
The James Webb Space Telescope has detected massive black holes (BHs) with
masses of $sim 10^{6-8}~M_odot$ within the first billion years of the
universe. One of the remarkable findings is the identification of "Little Red
Dots" (LRDs), a unique class of active galactic nuclei (AGNs) with distinct
characteristics representing a key phase in the formation and growth of early
BHs. Here, we analyze the occurrence rate of LRDs, which emerge around
redshifts $z sim 6-8$ and sharply decline at $z < 4$. We find that this trend
follows a log-normal distribution, commonly observed in phenomena driven by
stochastic and random factors. We propose a hypothesis that the first one or
two AGN events associated with newly-formed seed BHs are observed as LRDs and
their unique features fade in the subsequent episodes. This naturally explains
the cosmic evolution of AGN abundance over $0 < z < 5$, which follows $propto
(1+z)^{-5/2}$ due to the cumulative effect of recurring AGN activity. The
unique characteristics of LRDs are likely linked to the dense gas environments
around the seed BHs, which create strong absorption features in the broad-line
emission and enable super-Eddington accretion bursts, ultimately yielding the
observed overmassive nature of BHs compared to the local relationship.
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