  We have investigated the broad-line Balmer decrements (Halpha/Hbeta) for a
large, homogeneous sample of Seyfert 1 galaxies and QSOs using spectroscopic
data obtained in the Sloan Digital Sky Survey. The sample, drawn from the
Fourth Data Release, comprises 446 low redshift (z < 0.35) active galactic
nuclei (AGN) that have blue optical continua as indicated by the spectral
slopes in order to minimize the effect of dust extinction. We find that (i) the
distribution of the intrinsic broad-line Halpha/Hbeta ratio can be well
described by log-Gaussian, with a peak at Halpha/Hbeta=3.06 and a standard
deviation of about 0.03 dex only; (ii) the Balmer decrement does not correlate
with AGN properties such as luminosity, accretion rate, and continuum slope,
etc.; (iii) on average, the Balmer decrements are found to be only slightly
larger in radio-loud sources (3.37) and sources having double-peaked
emission-line profiles (3.27) compared to the rest of the sample. We therefore
suggest that the broad-line Halpha/Hbeta ratio can be used as a good indicator
for dust extinction in the AGN broad-line region; this is especially true for
radio-quiet AGN with regular emission-line profiles, which constitute the vast
majority of the AGN population.

Astrophysics