Computer Science
Scientific paper
Aug 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt.......130k&link_type=abstract
Ph.D. Thesis Tel-Aviv Univ., Israel.
Computer Science
Scientific paper
This work is aimed at measuring the size of the broad line region (BLR) in active galactic nuclei (AGNs) and establishing experimental relations between the luminosity, mass, and BLR size in these objects. It contains new observational results as well as data from the literature, and includes also new theoretical models of AGNs. The second chapter of the thesis presents the results of an intensive ground-based spectrophotometric campaign to monitor the Seyfert galaxy NGC 4151. No evidence for a time lag between the optical continuum and the UV continuum and emission lines has been found. For the H&alpha and H&beta emission lines, we find a time lag of 0-3 days; very different from past results where a time lag of 9+/-2 days was found for both lines. This may be due to a different variability timescale of the ionizing continuum, or to a real change in the BLR gas distribution. Results of 7.5 years of spectrophotometric monitoring of 28 Palomar-Green quasars are reported in chapter three. The typical sampling intervals are 1-4 months with typically 20-70 observing epochs per object. All sources show continuum and emission line variations, and all 17 objects with adequate sampling show Balmer line variations that follow the continuum variations with time lags of order 100 days. This work increases the available luminosity range for studying the size-mass-luminosity relations in AGNs by two orders of magnitude and doubles the number of objects suitable for such studies. Combining the results for the 17 quasars with previously obtained data for 17 Seyfert 1 galaxies in chapter four, we find that the BLR size scales with the 5100 Å luminosity as L0.70+/-0.03, significantly different from previous studies and from simple theoretical predictions. This suggests that the effective ionization parameter in AGNs may be a decreasing function of luminosity. Assuming gravitationally dominated motions of the line emitting gas, the central mass scales with the 5100 Å luminosity as M~L0.5+/-0.1. This is inconsistent with all AGNs having optical luminosity that is a constant fraction of the Eddington luminosity. Finally, chapter five presents a new scheme for modeling the BLR. This involves photoionization calculations of a large number of clouds, in several pre-determined geometries, and a comparison of the calculated line intensities with observed emission line light curves. Fitting several observed light curves simultaneously provides strong constraints on model parameters such as the run of density and column density across the nucleus, the shape of the ionizing continuum, and the radial distribution of the emission line clouds. Applying the model to the Seyfert 1 galaxy NGC 5548 enables us to successfully reconstruct four ultraviolet emission-line light curves.
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