A case study for hydromagnetic outflow in active galactic nuclei: NGC 5548

Details A case study for hydromagnetic outflow in active galactic nuclei: NGC 5548 A case study for hydromagnetic outflow in active galactic nuclei: NGC 5548

Jan 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt........48b&link_type=abstract

Thesis (PhD). UNIVERSITY OF KENTUCKY, Source DAI-B 60/11, p. 5563, May 2000, 143 pages.

Computer Science

Scientific paper

A hydromagnetic (MHD) wind from a clumpy molecular accretion disk surrounding a supermassive black hole is invoked to explain observed emission and absorption features of gas at UV and X-ray energies in Seyfert 1 galaxies. It is the first attempt to explain a wide range of phenomena observed on the periphery of Active Galactic Nuclei (AGN) with a single dynamical model and within the framework of the AGN unification scheme. In the first part of this thesis, the results of long- term observations of the broadline region (BLR) in the Seyfert 1 galaxy NGC 5548 are analyzed and a critical comparison with the predictions of a hydromagnetically- driven outflow model is provided. The model reproduces the basic features of C IV line variability in this AGN, i.e., time evolution of the profile shape and strength of the C IV emission line without varying the model parameters . The best fit model provides the effective size, the dominant geometry, the emissivity distribution and the 3D velocity field of the C IV BLR and constrains the mass of the central black hole to ~3×107 Msolar . The inner part of the wind in NGC 5548 appears to be responsible for the anisotropically emitted C IV line, while its outer part remains dusty and molecular, thus having similar spectral characteristics to a molecular torus. In addition, the model predicts a differential response across the C IV line profile, producing a red-side-first response in the relative velocity interval of 3,000 km s-1 to 6,000 km s -1 followed by the blue mid-wing and finally by the line core. In the second part of this dissertation, we have analyzed the UV and X-ray absorption in NGC 5548 within the framework of warm absorbing gas. We focus on two important issues: (1)compatibility of kinematics and dynamics of the MHD wind with the observed properties of warm absorbers; and (2)the relationship between the UV and X-ray absorbing gases. An in-depth comparison between the MHD wind model and the well-studied Seyfert 1 galaxy NGC 5548 is made, which at high spectral resolution exhibits a number of discrete UV absorption components. Our results show that for NGC 5548: (1)the total column densities of O VII, O VIII and H, inferred from X-ray observations are reproduced by constraining the UV ion column densities of C IV and N V in each component to lie within a factor of 2 of their observed values; (2)the warm absorbing gas exists in the outer part of the wind and is not a continuation of the flow in the broad emission-line region; and (3)the warm absorber extends both in radial and polar directions and is ionization stratified. Analysis shows that the discrete absorption components along the line-of-sight are intrinsically clumpy. The applicability of the MHD wind to warm absorbers is further tested by constructing a quasi-continuous flow model and extending it to arbitrary aspect angles. We find that the ratio of O VII to O VIII optical depths can serve as a new diagnostic of AGN aspect angle. (Abstract shortened by UMI.)

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