Samuel Lai (CSIRO Space & Astronomy)

Samuel Lai Colloquium: High-Redshift Ultraluminous Quasi-Stellar Objects

Kensington/Teams

Abstract

Over the past century, black holes transitioned from theoretical constructs to ubiquitous entities in the Universe. Extensive evidence supports the notion that supermassive black holes, which reside in the nuclear region of most mature galaxies, play an integral role in the assembly and dynamics of galactic material on cosmological timescales. However, the rapid evolution of supermassive black holes and their immediate environments in the early Universe (≲ 1 Gyr) is still poorly understood due to the paucity of robust constraints on physical accretion mechanisms, the limited statistical significance of available samples, and the scarcity of independent methodologies of black hole characterisation.
My work traces the evolution of super-massive black holes at high redshifts (z ∼ 5) using highly complete quasar samples with robustly-measured spectrophotometric properties. I build a spectroscopic analysis tool specifically designed for quasar spectra and apply it to a high-redshift quasar samples, measuring emission-lines (e.g. Si IV λ1398, O IV λ1402, C IV λ1549, Mg II λ2799, Hβ λ4863Å) and inferring black hole properties from mass, luminosity, and metallicity-sensitive features. I also present an analysis of quasar demographics in a z ~ 5 sample, measuring supermassive black hole growth. Furthermore, I showcase how thermal accretion disc models can be used to describe quasar spectral energy distributions. This approach has potential as a physically-motivated independent method that can aid in constraining properties of black holes. In summary, this research yields insights into the understanding of high-redshift supermassive black holes and their growth, equipping us with the necessary tools for detailed studies of quasar spectra.