Probing the inner regions of Active Galactic Nuclei through variability analysis

Abstract

Active Galactic Nuclei (AGN) are the some of the most luminous objects in the Universe, however their large distances and compact sizes limits our ability to directly study the physical processes that are occurring within their inner regions. Indirect methods are therefore necessary to probe the central regions, including analysing the strong variability that is a ubiquitous property of AGN emission. The motivation of this thesis is therefore to expand upon our knowledge of the inner regions of different types of AGN through in depth analysis of individual objects, as well as to prepare for the large influx of AGN that will be observed in future large scale surveys. Firstly, I present spectral and temporal variability analysis of the blazar PKS 0027-426 using optical and infrared (IR) observations. The results show that the emission from different wavelength ranges occurs either simultaneously, or on timescales smaller than the cadences of observations, and I further demonstrate that the emission could contain different contributions from multiple different coloured variable components within the different wavelength ranges. I then measure delays between the IR response to the optical light curves of the Seyfert 1 galaxy Zw229-015, and proceed to model the IR response using simulations of the dust distribution. The results show that the different IR wavelength ranges are likely dominated by the same hot dust emission, and that the observed IR emission is not well modelled by a single dust component, but the majority of dust is distributed in an inclined extended flat disk. Finally, I simulate mock AGN light curves in an attempt to understand the capabilities and limitations of recovering properties of the underlying power spectral density functions (PSDs) for AGN that will be observed with the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). I find that the ability to recover properties such as characteristic timescales or power law slopes is reasonably similar for the main proposed observing strategy and for the more frequent, deeper observations, however I also show that very few potential quasi-periodicities within the AGN light curves can be recovered with the current proposed LSST cadencing using this PSD analysis.

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ORCID for Ella Guise: orcid.org/0000-0002-5957-6202

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