Synchronized Co-evolution between Supermassive Black Holes and Galaxies Over the Last Seven Billion Years as Revealed by the Hyper Suprime-Cam

TL;DR

This study investigates the evolution of the black hole mass to galaxy stellar mass relation over the last seven billion years, finding it remains largely unchanged and tightly coupled, with implications for galaxy and black hole co-evolution.

Contribution

It provides the first constraints on the evolution and intrinsic scatter of the $M_{BH}-M_*$ relation using a large, uniformly-selected quasar sample at intermediate redshifts.

Findings

The $M_{BH}-M_*$ relation shows no significant evolution since z~0.8.

The intrinsic scatter of the relation is tightly constrained to about 0.25 dex.

The relation's evolution is degenerate with its intrinsic scatter, allowing for mild positive or negative evolution.

Abstract

We measure the evolution of the $M_{\rm BH}-M_*$ relation using 584 uniformly-selected SDSS quasars at $0.2<z<0.8$. The black-hole masses ($M_{\rm BH}$) are derived from the single-epoch virial mass estimator using the H$\beta$ emission line, and span the range $7.0<{\rm log}\,M_{\rm BH}/M_\odot<9.5$. The host-galaxy stellar masses ($M_*$), which cover the interval $10.0<{\rm log}\,M_* / M_\odot <11.5$, are determined by performing two-dimensional quasar-host decomposition of the Hyper Suprime-Cam images and spectral energy distribution fitting. To quantify sample-selection biases and measurement uncertainties on the mass terms, a mock quasar sample is constructed to jointly constrain the redshift evolution of the $M_{\rm BH}-M_*$ relation and its intrinsic scatter ($\sigma_\mu$) through forward modeling. We find that the level of evolution is degenerate with $\sigma_\mu$, such that both positive mild evolution (i.e, $M_{\rm BH}/M_*$ increases with redshift) with a small $\sigma_\mu$, and negative mild evolution with a larger $\sigma_\mu$ are consistent with our data. The posterior distribution of $\sigma_\mu$ enables us to put a strong constraint on the intrinsic scatter of the $M_{\rm BH}-M_*$ relation, which has a best inference of $0.25_{-0.04}^{+0.03}$ dex, consistent with the local value. The redshift evolution of the $M_{\rm BH}-M_*$ relation relative to the local relation is constrained to be $(1+z)^{0.12_{-0.27}^{+0.28}}$, in agreement with no significant evolution since $z\sim0.8$. The tight and non-evolving $M_{\rm BH}-M_*$ relation is suggestive of a coupling through AGN feedback or/and a common gas supply at work, thus restricting the mass ratio of galaxies and their black holes to a limited range. Given the considerable stellar disk component, the $M_{\rm BH}-M_{\rm bulge}$ relation may evolve as previously seen at higher redshifts.