Estimating dust attenuation from galactic spectra. II. Stellar and gas
  attenuation in star-forming and diffuse ionized gas regions in MaNGA
  We investigate the dust attenuation in both stellar populations and ionized
gas in kpc-scale regions in nearby galaxies, using integral field spectroscopy
data from MaNGA MPL-9. We identify star-forming (HII) and diffuse ionized gas
(DIG) regions from MaNGA datacubes. From the stacked spectrum of each region,
we measure the stellar attenuation, $E(B-V)_{\rm star}$, using the technique
developed by Li et al.(2020), as well as the gas attenuation, $E(B-V)_{\rm
gas}$, from the Balmer decrement. We then examine the correlation of
$E(B-V)_{\rm star}$, $E(B-V)_{\rm gas}$, $E(B-V)_{\rm gas}-E(B-V)_{\rm star}$
and $E(B-V)_{\rm star}/E(B-V)_{\rm gas}$ with 16 regional/global properties,
and for regions with different $\rm H{\alpha}$ surface brightnesses
($\Sigma_{\rm H\alpha}$). We find a stronger correlation between $E(B-V)_{\rm
star}$ and $E(B-V)_{\rm gas}$ in regions of higher $\Sigma_{\rm H\alpha}$.
Luminosity-weighted age ($t_L$) is found to be the property that is the most
strongly correlated with $E(B-V)_{\rm star}$, and consequently with
$E(B-V)_{\rm gas}-E(B-V)_{\rm star}$ and $E(B-V)_{\rm star}/E(B-V)_{\rm gas}$.
At fixed $\Sigma_{\rm H\alpha}$, $\log_{10}t_L$ is linearly and negatively
correlated with $E(B-V)_{\rm star}/E(B-V)_{\rm gas}$ at all ages. Gas-phase
metallicity and ionization level are important for the attenuation in the gas.
Our results indicate that the ionizing source for DIG regions is likely
distributed in the outer-skirt of galaxies, while for HII regions our results
can be well explained by the two-component dust model of Charlot & Fall (2000).
