School of Physical and Chemical Sciences, Te Kura Matū Seminar Series

Quasar Unification Via Accretion Disk Winds: From Phenomenology to Physics

Speaker

Professor Christian Knigge

Institute

Erskine Visitor in Astrophysics from the University of Southampton, UK

Time & Place

Fri, 11 May 2018 11:00:00 NZST in West 531

All are welcome

Abstract

Quasars (QSOs) and active galactic nuclei (AGN) display a bewildering array of observational properties. According to the standard unification model for AGN and QSOs, orientation effects are the main driver of this diversity. However, the physical origin of even most important spectroscopic signatures -- the so-called broad emisison/absorption lines (BALs and BELs) -- is not specified in this model and has remained largely unknown. In this talk, I will give an overview of a collaborative project aimed at testing the idea that most of the characteristic spectral features of AGN and QSOs are formed in accretion disk winds. More specifically, broad absorption lines (BALs) are produced for sight lines within the outflow, while broad emission lines (BELs) are observed for other viewing angles. In order to test these ideas, we use a state-of-the-art Monte Carlo radiative transfer and photoionization code to predict emergent spectra for a wide range of viewing angles and quasar properties (black hole mass, accretion rate, X-ray luminosity, etc). We are also using our code to test and improve hydrodynamic disk wind models for quasars. So far, we have been able to demonstrate that the treatment of ionization in existing hydrodynamic models of line-driven disk winds is too simplistic to yield realistic results: the modelled outflows would be strongly over-ionized and hence would not feel the line-driving forces that are assumed to produce them. Finally, we can also predict the reverberation signatures produced by disk winds, which can be directly compared to the results of the latest reverberation mapping campaigns.

Biography

I am a Professor of Astrophysics in the Astronomy Group at the University of Southampton. My research interests include accretion onto compact objects, binary evolution, stellar exotica in globular clusters, type Ia supernovae and their progenitors, Galactic plane surveys, (astro-) statistics, and the physics of accretion and outflows in quasars.