Physics and Astronomy
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Browsing Physics and Astronomy by Subject "Active galactic nuclei"
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Item Open Access Disc Winds and Line-Width Distributions in Active Galactic Nuclei(2016-09-20) Chajet, Laura Susana; Hall, Patrick BWe study Active Galactic Nucleus (AGN) emission-line profiles by combining an improved version of the accretion disc-wind model of Murray & Chiang with the magnetohydrodynamic model of Emmering et al. We consider central objects with different masses and/or luminosities. We show how the shape, broadening and shift of the C IV line depend not only on the viewing angle to the object but also on the wind launching angle, especially for small launching angles. We have compared the dispersions in our model C IV line-width distributions to observational upper limits on that dispersion, considering both smooth and clumpy torus models. Following Fine et al., we transform that scatter in the profile line-widths into a constraint on the torus geometry. We show how the half-opening angle of the obscuring structure depends on the mass and luminosity of the central object.Item Open Access Stars Versus Quasar Accretion Disks(2023-08-04) Seaton, Lucas Matthew; Hall, Patrick B.This thesis investigates the astrophysical effects of stars colliding with the accretion disks of supermassive black holes (SMBH) in active galactic nuclei (AGN). In this work, we model the AGN to have a thin accretion disk surrounded by a stellar nuclear cluster (SNC) containing stars on various orbital eccentricities and inclination angles striking the disk at periapse. An impacting star carves a tilted cylindrical tunnel out of the disk material and loses up to $6\times10^{-4}\%$ of its stellar mass. The time-averaged collisional luminosity is at most $10^{-2}$ times the entire disk's expected luminosity, while the emission profile of an impact site initially flares before quickly dimming to the brightness of the local disk. The parameters of the SMBH, accretion disk, SNC, and impacting stars are altered to reveal that star-disk collisions from a densely populated SNC can outshine the disk luminosity.