Quasi-stellar Objects and Their Host Galaxies from a Mass-based Viewpoint using Gravitational Lensing and Spectral Analysis

Abstract

It is unclear how galaxies and their central supermassive black holes (SMBHs) coevolve across cosmic time, especially for the nonlocal universe (z > 0.5). This thesis presents our attempts to understand this coevolution through the High-z Universe probed via Lensing by QSOs (HULQ) project, which utilizes quasi-stellar object (QSO) host galaxies acting as gravitational lenses (QSO lenses) to obtain the host galaxy mass independent from its light profile.

The first part of this thesis focuses on the feasibility of this project, that is, whether sufficiently large numbers of QSO lenses are expected to be found in various concurrent and future imaging surveys. We find that ~ 440 QSO lenses will reside in the Hyper Suprime-Cam Wide survey (HSC/Wide), which is expected to be the most prolific concurrent survey, with this number being boosted by one to two orders of magnitude (to ~10,000) with upcoming surveys such as that conducted with the Large Synoptic Survey Telescope (LSST). We discuss several methods of how to study the redshift evolution of the M_BH - sigma relation, which is a standout illustration of the coevolution. In addition, we demonstrate how the intimacy of lensed images to the bright deflector QSO for most systems will affect the detectability of QSO lenses. We estimate that only ~ 82 and 900 will be detectable for HSC/Wide and LSST, respectively; the decrease is significant yet still yields an acceptable sample for the main objective. This decrease will be less of a problem for space-based imaging surveys, for their small point spread function FWHMs will allow detections of lensed images lying relatively close to the deflector QSO, and thus unveil the less massive yet more numerous QSO hosts.

In the second part of this thesis, we present the results of the QSO lens search using HSC/Wide data, and also the spectroscopic observation of a QSO lens candidate from the HULQ project, HULQ J0002+0239, which consists of a QSO host galaxy at z_d = 1.455 and four seemingly lensed objects in a cross-like configuration. Deep optical spectra of two of the possibly lensed objects with z ~ 24.5 mag were obtained with the Gemini Multi-Object Spectrograph on the Gemini North Telescope. Their spectra reveal that the objects are at z=0.29 and z=1.11, and we conclude that HULQ J0002+0239 is not a QSO lens. We also demonstrate that these results are in agreement with the predicted number of QSO lenses, and discuss the prospect of the HULQ project.

To examine the SMBH-galaxy correlations for QSO host galaxies, M_BH measurements for the QSOs are also required. In the third part of this thesis, we measure the virial M_BH estimates of ~ 710,000 QSOs from the Sloan Digital Sky Survey Data Release 16 Quasar Catalog. We conduct spectral fitting for each of the QSO spectra and measure the monochromatic luminosity and various line widths (FWHM, MAD, and sigma) of each QSO. Ten different calibrators across three broad lines (Hbeta, [Mg II], and [C IV]) are used for the M_BH estimates, and one for each broad line for a total of three calibrators are selected to be reliable: the FWHM-based Hbeta calibrator from Vestergaard & Peterson (2006), the FWHM-based [Mg II] calibrator from Vestergaard & Osmer (2009), and the FWHM-based [C IV] calibrator from Vestergaard & Peterson (2006). In addition, we present the bolometric luminosity and Eddington ratio for each QSO, which shows that the Eddington ratio distribution shows no significant change up to z ~ 5.

This thesis has displayed how to study QSOs and their host galaxies from a mass-based viewpoint. We have demonstrated the use of gravitational lensing to study the evolution of the M_BH - sigma relation, have initiated a survey for QSO lenses, and have virially estimated M_BH for the largest QSO sample known to date. These studies will be cornerstones for investigating the coevolution between SMBHs and galaxies over the age of the universe.