MSc defence by Maria Fevre Vestergaard Kronskov
Title: Investigating Fundamental Properties of Accreting Supermassive Black Holes in Active Galactic Nuclei
Supervisors: Marianne Vestergaard and Sandra Raimundo
Abstract: The accretion disk in an active galactic nucleus (AGN) is the driver of the AGN. Understanding the physics of the accretion disk can provide knowledge of the AGN fuel and fueling mechanisms. The accretion disk is affected by the spin of the black hole, which can provide clues on e.g. past galaxy events as mergers, fueling mechanisms and evolution of the host galaxy. Mass accretion rates are often estimated with bolometric luminosities, providing large uncertainties, and black hole spins are usually not well constrained due to the degeneracy with other physical parameters. Many studies using theoretical models of the AGN emission, use average values for physical parameters. Average accretion disk inclinations are commonly used because of the lack of individual estimates. I investigate the precision of the mass accretion rate estimates of a sample of five Seyfert 1 galaxies with individual inclination estimates, by fitting a thin disk model to optical spectral data. I propagate the errors on black hole mass and disk inclination, and analyze the significance of the intrinsic reddening correction errors. All my mass accretion rate estimates are within the range M_dot = 0:001-0:06M_sun/yr, agreeing with common Seyfert 1 values. I find propagated mass accretion rate errors of +/-42-71% and errors of <+/-725% from the intrinsic reddening correction. I find that individual accretion disk inclination estimates are unnecessary in highly reddened AGN. To constrain the spin, I analyze the Narrow-Line Seyfert 1 (NLS1), Ark 564. I analyze the optical-X-ray SED in Ark 564 because the NLS1 accretion disk contributes in X-rays. I use the model OPTXAGNF, of the accretion disk and corona to estimate the optical depth, and electron temperature of the disk Comptonization, kT, to tau = 15.4 +/- 0.1 and kT = 0.224 +/- 0.004 keV, and the Eddington ratio, L_Bol/L_Edd, to L_Bol/L_Edd = 1.021+/-0.007. I constrain the black hole mass and -spin to M = 8 * 10^6 M_sun and a_*= 0. All results agree with predictions and earlier studies of Ark 564. I find that the model is a good description of the accretion disk- and corona physics, but a few more free parameters will improve the fit results. The first part of my work shows the importance of having good tools for estimating intrinsic reddenings. The errors I estimate can be used as guidance in future studies where errors are not propagated. The second part of my work can be a part of a larger study of black hole spins in order to provide clues of past galaxy feeding and merger events, and the evolution of the host galaxy.