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

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 $\sim 3\times 107M\odot$. 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.)...