A dormant, overmassive black hole in the early Universe

Kavli Affiliate: Roberto Maiolino

| First 5 Authors: Ignas JuodĹžbalis, Roberto Maiolino, William M. Baker, Sandro Tacchella, Jan Scholtz

| Summary:

Recent observations have found a large number of supermassive black holes
already in place in the first few hundred million years after Big Bang. The
channels of formation and growth of these early, massive black holes are not
clear, with scenarios ranging from heavy seeds to light seeds experiencing
bursts of high accretion rate. Here we present the detection, from the JADES
survey, of broad Halpha emission in a galaxy at z=6.68, which traces a black
hole with mass of ~ 4 * 10^8 Msun and accreting at a rate of only 0.02 times
the Eddington limit. The host galaxy has low star formation rate (~ 1 Msun/yr,
a factor of 3 below the star forming main sequence). The black hole to stellar
mass ratio is ~ 0.4, i.e. about 1,000 times above the local relation, while the
system is closer to the local relations in terms of dynamical mass and velocity
dispersion of the host galaxy. This object is most likely the tip of the
iceberg of a much larger population of dormant black holes around the epoch of
reionisation. Its properties are consistent with scenarios in which short
bursts of super-Eddington accretion have resulted in black hole overgrowth and
massive gas expulsion from the accretion disk; in between bursts, black holes
spend most of their life in a dormant state.

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