On the Connection between Supermassive Black Holes and Galaxy Growth in the Reionization Epoch

Abstract

The correlation between the mass of supermassive black holes (SMBHs;  BH ) and their host galaxies (  ⋆ ) in the reionization epoch provides valuable constraints on their early growth. High-redshift quasars typically have an  BH /  ⋆ ratio significantly elevated in comparison to the local value. However, the degree to which this apparent offset is driven by observational biases is unclear for the most distant quasars. To address this issue, we model the sample selection and measurement biases for a compilation of 20 quasars at z ∼ 6 with host properties based on ALMA observations. We find that the observed distribution of quasars in the  BH –  ⋆ plane can be reproduced by assuming that the underlying SMBH population at z ∼ 6 follows the relationship in the local universe. However, a positive or even a negative evolution in  BH /  ⋆ can also explain the data, depending on whether the intrinsic scatter evolves and on the strength of various systematic uncertainties. To break these degeneracies, an improvement in the accuracy of mass measurements and an expansion of the current sample to lower  BH limits are needed. Furthermore, assuming a radiative efficiency of 0.1 and quasar duty cycles estimated from the active SMBH fraction, significant outliers in  BH /  ⋆ tend to move toward the local relation given their instantaneous BH growth rate and star formation rate. This may provide evidence for a self-regulated SMBH–galaxy coevolution scenario that is in place at z ∼ 6, with active galactic nucleus feedback being a possible driver.

Supercritical Growth Pathway to Overmassive Black Holes at Cosmic Dawn: Coevolution with Massive Quasar Hosts

“…However, those quasars represent the tip of the iceberg of the high-z BH population found in shallow surveys (e.g., SDSS) rather than the underlying populations detected in deeper surveys (e.g., Subaru Hyper Suprime-Cam (HSC); Matsuoka et al 2016;Onoue et al 2019;Izumi et al 2021). The mass ratio for the bulk population inferred from current observations seems consistent with the local value within errors owing to the intrinsic scatter and the strength of various systematic uncertainties (Li et al 2022). Further improvements of the mass measurements and exploration of less luminous quasars are required to better understand the physical origin of the BHgalaxy coevolution.…”

Quasar Luminosity Function at z = 7

“…The similar epoch of turnover (i.e., to accelerating decline toward the highest redshifts) at different luminosities may indicate that the density evolution is governed by different physics from that drives the downsizing at lower redshifts. Comparison of the present LF measurements with theoretical models (e.g., Kroupaet al 2020;Li et al 2022;Oogi et al 2022) will be a subject of future papers.…”

TRINITY II: The Luminosity-dependent Bias of the Supermassive Black Hole Mass--Galaxy Mass Relation for Bright Quasars at $z=6$

“…In this work, we examine the systematic bias in the observed M • -M * relation for luminosity-limited quasar samples, as well as contributions to the z = 6 quasar bolometric luminosity function from SMBHs at different offsets relative to the z = 6 M • -M * relation. Compared to previous studies like Li et al (2022) that adopt empirically determined Eddington ratio distributions and intrinsic M • -M * relations at z = 0, we make inferences based on the joint SMBH mass-Eddington ratio distributions at different redshifts from TRINITY, which are: 1) explicitly constrained by galaxy and SMBH data ( §3), and 2) self-consistent with the reconstructed SMBH growth histories. Our key findings are:…”

“…In the absense of scatter around the M • -M * relation, there will be no such selection bias, because every single quasar in the sample will lie perfectly on the scaling relation. To estimate the extent of Lauer bias, one thus needs: 1) the scatter around the intrinsic M • -M * relation; and 2) the underlying Eddington ratio distributions for SMBHs in different galaxies (see, e.g., Li et al 2022).…”