The Sizes of Quasar Host Galaxies with the Hyper Suprime-Cam Subaru Strategic Program

TL;DR

This study analyzes the sizes and properties of ~5000 quasar host galaxies using Hyper Suprime-Cam data, revealing their typical disk-like structure, size-mass relation, and the influence of dust on quasar visibility.

Contribution

It provides a large-scale, automated analysis of quasar host galaxy sizes and structures, comparing them with inactive galaxies and exploring implications for galaxy and black hole co-evolution.

Findings

Quasar hosts are mostly massive, star-forming, disk-like galaxies.

Their sizes follow a size-stellar mass relation similar to inactive galaxies.

Quasar hosts are more compact than star-forming galaxies but less so than quiescent ones.

Abstract

The relationship between quasars and their host galaxies provides clues on how supermassive black holes (SMBHs) and massive galaxies are jointly assembled. To elucidate this connection, we measure the structural and photometric properties of the host galaxies of ~5000 SDSS quasars at 0.2<z<1 using five-band (grizy) optical imaging from the Hyper Suprime-Cam Subaru Strategic Program. An automated analysis tool is used to forward-model the blended emission of the quasar as characterized by the point spread function and the underlying host galaxy as a two-dimensional Sersic profile. In agreement with previous studies, quasars are preferentially hosted by massive star-forming galaxies with disk-like light profiles. Furthermore, we find that the size distribution of quasar hosts is broad at a given stellar mass and the average values exhibit a size-stellar mass relation as seen with inactive galaxies. In contrast, the sizes of quasar hosts are more compact than inactive star-forming galaxies on average, but not as compact as quiescent galaxies of similar stellar masses. This is true irrespective of quasar properties including bolometric luminosity, Eddington ratio, and black hole mass. These results are consistent with a scenario in which galaxies are concurrently fueling a SMBH and building their stellar bulge from a centrally-concentrated gas reservoir. Alternatively, quasar hosts may be experiencing a compaction process in which stars from the disk and inflowing gas are responsible for growing the bulge. In addition, we confirm that the host galaxies of type-1 quasars have a bias of being closer towards face-on, suggesting that galactic-scale dust can contribute to obscuring the broad-line region.