What do observations tell us about the highest-redshift supermassive black holes?

Abstract

I review the current understanding of some key properties of the earliest growing supermassive black holes (SMBHs), as determined from the most up-to-date observations of z ≲ 5 quasars. This includes their accretion rates and growth history, their host galaxies, and the large-scale environments that enabled their emergence less than a billion years after the Big Bang. The available multi-wavelength data show that these SMBHs are consistent with Eddington-limited, radiatively efficient accretion that had to proceed almost continuously since very early epochs. ALMA observations of the hosts’ ISM reveal gas-rich, well developed galaxies, with a wide range of SFRs that may exceed ∼1000 Mȯyr−1. Moreover, ALMA uncovers a high fraction of companion, interacting galaxies, separated by < 100 kpc (projected). This supports the idea that the first generation of high-mass, luminous SMBHs grew in over-dense environments, and that major mergers may be important drivers for rapid SMBH and host galaxy growth. Current X-ray surveys cannot access the lower-mass, supposedly more abundant counterparts of these rare z ≳ 5 massive quasars, which should be able to elucidate the earliest stages of BH formation and growth. Such lower-mass nuclear BHs will be the prime targets of the deepest surveys planned for the next generation of facilities, such as the upcoming Athena mission and the future Lynx mission concept.

SMBH seeds from dissipative dark matter

“…SMBHs seeded and decoupled at higher redshift can populate the low-mass end of the SMBH mass function. Quasar surveys and theoretical modelling indicate that the number density of luminous high redshift quasars with M BH 10 9 M and L bol 10 46 erg/s is 10 119,120], which sets a lower limit of the abundance of underlying SMBH population. 2 The predictions here are consistent with this limit.…”

Past, Present, and Future of the Scaling Relations of Galaxies and Active Galactic Nuclei

“…There are intriguing caveats with the interpretation of a rapid black hole growth. First, very massive seed black holes need to be formed at z ≈ 20 to account for masses ∼ 10 9 M ⊙ observed at redshift z ≳ 4 ( (Volonteri, 2010;Trakhtenbrot, 2020), and references therein). Second, BH masses (unlike the masses of galaxies!)…”

Supermassive Black Holes from Bose-Einstein Condensed Dark Matter—Or Black and Dark Separation by Angular Momentum

“…This limiting mass M K is called the Kaup mass, and the exact value M K = 0.633 m 2 P /m is derived from numerical calculations based on general relativity [30]. This mass is far smaller than the popular limiting mass for Baryons m 3 P /m 2 . However, this Kaup mass sets the lower bound of the BH formed from bosonic DM.…”

“…Recent observations have revealed a tremendous number of supermassive black holes (SMBH) of mass 10 6 -10 10 M in the wide range of redshift up to z ≈ 7.642 [1][2][3]. SMBH seems to be a common astronomical species everywhere in the Universe from the very early stage.…”