Description
The ionizing spectral energy distribution (SED) of active galactic nuclei (AGN) is a fundamental, yet poorly constrained quantity that governs the photoionization of the Broad Line Region (BLR). X-ray observations of the changing-look AGN Mrk 590 by Lawther et al. (2025) have revealed a Comptonizing inner accretion flow, providing a new constraint on the SED. This thesis uses the Cloudy photoionization code to test whether this newly determined SED can reproduce the observed broad emission line intensities in Mrk 590.
UV and optical spectra from instruments are fitted using a custom spectral decomposition pipeline to measure emission line intensities. These measurements are compared against Cloudy photoionization model grids computed for a range of physical conditions, including varying hydrogen column densities, hydrogen ionization parameters, and gas densities. The grids are generated using version 25 of Cloudy and use the ionizing SED composed from Lawther et al. (2025) as input.
A key goal is to assess whether the X-ray-derived SED produces line intensities consistent with the observations, or whether additional constraints on the SED shape are needed. Furthermore, the photoionization modelling is applied to investigate whether Mrk 590's incident SED is consistent with that expected from a standard accretion disk, or whether this changing-look AGN possesses unusual physical properties. Current research suggests the latter, pointing toward an SED that deviates from standard disk models. This study contributes to a broader understanding of the connection between AGN ionization physics and BLR emission properties.
| Field of study | Astrophysics |
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| Supervisor | Marianne Vestergaard |