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

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 Sloan Digital Sky Survey 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 Sérsic profile. We find that quasars are preferentially hosted by massive star-forming galaxies with disklike light profiles. Furthermore, 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 those of inactive star-forming galaxies on average, but not as compact as those of quiescent galaxies of similar stellar masses. This is true irrespective of quasar properties, including the bolometric luminosity, Eddington ratio, and black hole mass. These results are consistent with a scenario in which galaxies are concurrently fueling an 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 to face-on systems, suggesting that galactic-scale dust can contribute to obscuring the broad-line region.

Concordance between Observations and Simulations in the Evolution of the Mass Relation between Supermassive Black Holes and Their Host Galaxies

“…The observed sample consists of 646 uniformly selected SDSS quasars at 0.2 < z < 0.8, imaged by Subaru/HSC (Li et al 2021a), and 32 quasars at 1.2 < z < 1.7 as imaged by HST (Ding et al 2020a, hereafter D20). The latter are selected from three deep-survey fields, namely, COSMOS (Civano et al 2016), (E)-CDFS-S (Lehmer et al 2005;Xue et al 2011), and SXDS (Ueda et al 2008).…”

“…A sample of ∼5000 type 1 SDSS quasars from the DR14 catalog (Pâris et al 2018) at 0.2 < z < 1 has been imaged by the high-resolution Subaru Strategic Program (SSP) wide-area survey (Aihara et al 2019) using HSC (Miyazaki et al 2018). With accurate point-spread function (PSF) models in five optical bands grizy, two-dimensional quasar-host decompositions have been performed (Li et al 2021a) to obtain the flux and color of each quasarʼs host galaxy. The state-of-the-art image modeling software lenstronomy (Birrer et al 2015;Birrer & Amara 2018;Birrer et al 2021) is adopted to perform the modeling task.…”

“…The mass ranges for the entire sample are log(M * ) ä [9.0, 11.5] M e and log(M BH ) ä [6.5, 10.0] M e . We refer the reader to Section 4.2 in Li et al (2021a) for more details.…”

Inferences on Relations between Distant Supermassive Black Holes and Their Hosts Complemented by the Galaxy Fundamental Plane

“…Typical uncertainties are ∼0.4 dex. Li et al (2021a) provides the stellar mass and size of their host galaxies. This is achieved by decomposing the optical images into the quasar and host galaxy contributions with accurate knowledge of the point-spread function.…”

“…A large simulated sample is needed to ensure sufficient numbers of massive cases. We then randomly assign a size (i.e., half-light radius) using the best-fit relations and their intrinsic dispersion given in Li et al (2021a) for quasar hosts. As a check, we repeat the analysis using a size distribution based on Sérsic fits to 1.5 million galaxies covering ∼100 deg 2 of the HSC-SSP (Kawinwanichakij et al 2021), which have been measured using the same analysis tool as applied to the quasars.…”