The X–shooter/ALMA Sample of Quasars in the Epoch of Reionization. II. Black Hole Masses, Eddington Ratios, and the Formation of the First Quasars

Abstract

We present measurements of black hole masses and Eddington ratios (λ Edd) for a sample of 38 bright (M 1450 < −24.4 mag) quasars at 5.8 ≲ z ≲ 7.5, derived from Very Large Telescope/X–shooter near–IR spectroscopy of their broad C iv and Mg ii emission lines. The black hole masses (on average, M BH ∼ 4.6 × 109 M ⊙) and accretion rates (0.1 ≲ λ Edd ≲ 1.0) are broadly consistent with that of similarly luminous 0.3 ≲ z ≲ 2.3 quasars, but there is evidence for a mild increase in the Eddington ratio above z ≳ 6. Combined with deep Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [C II] 158 μm line from the host galaxies and VLT/MUSE investigations of the extended Lyα halos, this study provides fundamental clues to models of the formation and growth of the first massive galaxies and black holes. Compared to local scaling relations, z ≳ 5.7 black holes appear to be over-massive relative to their hosts, with accretion properties that do not change with host galaxy morphologies. Assuming that the kinematics of the T ∼ 104 K gas, traced by the extended Lyα halos, are dominated by the gravitational potential of the dark matter halo, we observe a similar relation between black hole mass and circular velocity as reported for z ∼ 0 galaxies. These results paint a picture where the first supermassive black holes reside in massive halos at z ≳ 6 and lead the first stages of galaxy formation by rapidly growing in mass with a duty cycle of order unity. The duty cycle needs to drastically drop toward lower redshifts, while the host galaxies continue forming stars at a rate of hundreds of solar masses per year, sustained by the large reservoirs of cool gas surrounding them.

The Assembly of Black Hole Mass and Luminosity Functions of High-redshift Quasars via Multiple Accretion Episodes

“…For illustration purposes, we scale the normalization of the ERDFs with the luminosity cuts, multiplied by a factor of 5 and 30, respectively. The Eddington ratio for the whole sample follows a Schechter shape with a majority of inactive quasars, while the observed Eddington ratio is biased toward higher values and the distribution results in a lognormal shape, consistent with that of the brightest quasars at z ∼ 6 (e.g., Willott et al 2010b;Shen et al 2019;Yang et al 2021;Farina et al 2022). The lognormal shape still holds with the lower luminosity cut, but a lower luminosity threshold allows us to unveil more hidden quasars with low Eddington ratios.…”

A SPectroscopic Survey of Biased Halos in the Reionization Era (ASPIRE): A First Look at the Rest-frame Optical Spectra of z > 6.5 Quasars Using JWST

“…Observations of luminous z  6.5 quasars have revealed the existence of supermassive black holes (SMBHs) and their massive host galaxies in the reionization epoch. The measurements of high-redshift quasar BH masses suggest that 10 8-9 solar-mass SMBHs existed as early as 700 million yr after the Big Bang, challenging models of early SMBH growth and BH seed formation (e.g., Bañados et al 2018;Yang et al 2020;Wang et al 2021;Yang et al 2021;Farina et al 2022). Measuring BH masses accurately is the key step required to characterize the growth and evolution of early SMBHs.…”

“…Thus, the measurements of SMBHs in quasars at z > 4 are mainly based on broad emission lines in the rest-frame UV (e.g., C IV λ1549 and Mg II λ2800). The Mg IIbased BH mass estimators are widely used for the measurements of reionization-era SMBHs (e.g., Shen et al 2019;Yang et al 2021;Farina et al 2022). However, the study of quasar BH masses at low redshift via RM and the comparison between multiple single-epoch BH mass estimators have established the Hβ line as the most reliable tracer among quasar UV/optical emission lines (e.g., Shen 2013; Wang et al 2020).…”

Splitting the lentils: Clues to galaxy/black hole coevolution from the discovery of offset relations for non-dusty versus dusty (wet-merger-built) lenticular galaxies in theMbh–M*,spheroid andMbh–M*,galaxy diagrams

“…Studies of CO and other molecules, such as hydrogen cyanide (HCN), in the discs of high-z galaxies offer exciting pathways to witness further the growth of black holes and the metamorphosis of their host galaxies (e.g. Riechers 2007;Kakkad et al 2017;Farina et al 2022;Tripodi et al 2022, and references therein). Awareness of the morphology-dependent black hole scaling relations will be necessary for the comparison with local galaxies and interpretation.…”