BS in Physics
Vardha N. Bennert
A sample of ∼100 type-1 local (0.02 ≤ z ≤ 0.1) active galaxies (AGNs) was selected from the Sloan Digital Sky Survey with black hole masses MBH > 107 Mʘ and re-observed using the Keck 10-m telescope to study the local scaling relations between MBH and the host galaxy properties. As a side product, the data provides insight into any changes of the broad-line region within the 3-9 year time-frame covered by the two sets of spectra. The variability of the broad Hβ emission line is of particular interest to us, not only because it is used to estimate MBH, but also because its presence and width acts as a classifier for the so-called Seyfert-type of these galaxies. Roughly 44% of the sample show significant broad-line variability with a change in Seyfert classification, questioning the standard unified model for active galaxies in which the AGN type depends only on viewing angle. The observed type change cannot simply be explained by a drop in black hole accretion rate, as traced by the AGN power-law continuum. Also, we do not find evidence for obscuration to play the dominant role in the observe change in Hβ line width. More data are needed to determine the origin of the line profile changes. While similar dramatic transitions have been reported in the literature, our study is the first to provide statistical information.