BROAD Hβ EMISSION-LINE VARIABILITY IN A SAMPLE OF 102 LOCAL ACTIVE GALAXIES

Abstract

A sample of 102 local (0.02 ≤ z ≤ 0.1) Seyfert galaxies with black hole masses M BH  > 10 7 M ⊙ was selected from the Sloan Digital Sky Survey (SDSS) and observed using the Keck 10 m telescope to study the scaling relations between M BH and host galaxy properties. We study profile changes of the broad H β emission line within the three to nine year time frame between the two sets of spectra. The variability of the broad H β emission line is of particular interest, not only because it is used to estimate M BH , but also because its strength and width are used to classify Seyfert galaxies into different types. At least some form of broad-line variability (in either width or flux) is observed in the majority (∼66%) of the objects, resulting in a Seyfert-type change for ∼38% of the objects, likely driven by variable accretion and/or obscuration. The broad H β line virtually disappears in 3/102 (∼3%) extreme cases. We discuss potential causes for these changing look active galactic nuclei. While similar dramatic transitions have previously been reported in the literature, either on a case-by-case basis or in larger samples focusing on quasars at higher redshifts, our study provides statistical information on the frequency of H β line variability in a sample of low-redshift Seyfert galaxies.