Reddening of the BLR and NLR in AGN From a Systematic Analysis of Balmer
  Decrement
  We selected an active galactic nuclei (AGN) sample ($0 < z \le 0.35$) from
Sloan Digital Sky Survey Data Release 7, and measured the broad- (${\rm
H\alpha^{b}/H\beta^{b}}$) and narrow-line Balmer decrements (${\rm
H\alpha^{n}/H\beta^{n}}$) of 554 selected AGNs. We found that the distributions
of Balmer decrements can be fitted by a Gaussian function and give the best
estimates of ${\rm H\alpha^{b}/H\beta^{b}} = 3.16$ with a standard deviation
0.07 dex, and ${\rm H\alpha^{n}/H\beta^{n}} = 4.37$ with a standard deviation
0.10 dex. We inspected the distributions of ${\rm H\alpha^{b}/H\beta^{b}}$ and
${\rm H\alpha^{n}/H\beta^{n}}$ in the Baldwin$-$Phillips$-$Terlevich (BPT)
diagram and found that only narrow-line Balmer decrements depend on the
physical conditions of the narrow-line region (NLR). We tested the relationship
between ${\rm H\alpha^{b}/H\beta^{b}}$ and ${\rm H\alpha^{n}/H\beta^{n}}$, and
found that ${\rm H\alpha^{b}/H\beta^{b}}$ does not correlate with ${\rm
H\alpha^{n}/H\beta^{n}}$. We investigated the relationship between Balmer
decrements and Seyfert sub-type, and found that only broad-line Balmer
decrements correlate with Seyfert sub-type, We also examined the dependency of
Balmer decrements on AGN properties, and found that Balmer decrements have no
correlation with optical luminosity, but show some dependence on accretion
rate. These results indicate that the NLR is subject to more reddening by dust
than the broad-line region (BLR).
