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Outflows and Dust in Quasars


Type

Thesis

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Authors

Abstract

Supermassive black holes (SMBHs) at the centres of galaxies are known to actively accrete, forming so-called active galactic nuclei' (AGN) or quasars'. These AGN are believed to feed back energy into their host galaxies, regulating star formation and the growth of the SMBH itself. This thesis investigates the outflow properties in quasars at 1<z<3, corresponding to the peak epoch of galaxy formation and SMBH growth.

First, I make use of recent improvements to atomic energy-level data and photoionisation models to constrain the properties of the Fe III emitting material in quasars. I show that this material must be dense and micro-turbulent to explain the observed strength of emission, and thus arise from the inner parts of the broad line region. The strength of this emission is shown to correlate with the outflow properties.

Second, I develop an SED model capable of reproducing the median observed photometric colours in the SDSS quasar population. This model is then used to investigate the properties of the emission from the hottest, sublimation-temperature dust components in the near infrared spectra of quasars. This dust is believed to be located at the inner edge of the toroidal obscuring structure. The strength of hot dust emission is found to correlate with the quasar outflow properties, providing evidence of a link between the broad line region and the dusty structures surrounding the inner regions of the AGN.

Finally, I quantify the outflow properties in a sample of heavily dust-reddened quasars. When matched in redshift and luminosity, there is no significant difference between the outflow kinematics of reddened and unobscured quasars. Assuming a paradigm in which dust-reddened quasars arise from major galaxy mergers, quasar-driven outflows must therefore persist after the obscuring dust is cleared from the line of sight.

Description

Date

2020-09-25

Advisors

Banerji, Manda
Hewett, Paul

Keywords

quasars:general

Qualification

Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
Sponsorship
STFC (1952037)
UKRI: Science and Technology Funding Council (STFC)