The reverberation signatures of accretion disk winds in active galactic nuclei

Abstract

Active Galactic Nuclei are the most luminous objects in the universe; objects that can outshine their host galaxies by orders of magnitude, but are incredibly compact. Some models for AGN describe them as super-massive black holes surrounded by accretion disks of in owing matter and outflowing 'winds' of material. As the central regions of AGN, responsible for the bulk of the emission, are on the scale of light-months whilst AGN are Mly distant, they are unresolvable.

As such, we must turn to other techniques to investigate their properties. Reverberation mapping is commonly used to estimate black hole masses in AGN using the delayed response of broad emission lines in their spectra to fluctuations in the underlying continuum. Velocity-resolved reverberation mapping offers an effective tool for determining the structure and kinematics of the broad-line region (BLR) that emits these lines, including the accretion disk and winds. Much prior work has been performed using simulations of simplified models to generate the response functions associated with a range of basic geometries. However, no model has included both full ionisation and radiative transfer effects, and a complex geometry with rotation and outflow.

In this thesis, the Monte Carlo radiative transfer and ionisation code Python has been modified for use in reverberation mapping of a range of geometries, from simple to potentially more realistic. Building on prior work, we model the BLR response to the central ionising continuum source taking into account detailed radiative transfer effects and self-consistent calculations of the ionisation state of the disk wind. We find the response functions generated display features that can confound existing analysis, including negative responses. We then test the ability of existing techniques to recover these more complex response functions from simulated observing campaigns.

In summary, this thesis demonstrates that radiative transfer and ionisation effects are crucial for generating response functions for realistic geometries and kinematics, and highlights the limits of existing techniques to accurately recover physically-motivated response functions.

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Identifiers

ORCID for Samuel W. Mangham: orcid.org/0000-0001-7511-5652

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