The Star Formation Reference Survey. II. Activity demographics and
  host-galaxy properties for Infrared-selected galaxies
  We present activity demographics and host-galaxy properties of
infrared-selected galaxies in the local Universe, using the representative Star
Formation Reference Survey (SFRS). Our classification scheme is based on a
combination of optical emission-line diagrams (BPT) and IR-color diagnostics.
Using the weights assigned to the SFRS galaxies based on its parent sample, a
far-infrared-selected sample comprises 71\% H\,\textsc{ii} galaxies, 13\%
Seyferts, 3\% Transition Objects (TOs), and 13\% Low-Ionization Nuclear
Emission-Line Regions (LINERs). For the SFRS H\,\textsc{ii} galaxies we derive
nuclear star-formation rates and gas-phase metallicities. We measure
host-galaxy metallicities for all galaxies with available long-slit
spectroscopy and abundance gradients for a subset of 12 face-on galaxies. The
majority of H\,\textsc{ii} galaxies show a narrow range of metallicities, close
to solar, and flat metallicity profiles. Based on their host-galaxy and nuclear
properties, the dominant ionizing source in the far-infrared selected TOs is
star-forming activity. LINERs are found mostly in massive hosts (median of
$10^{10.5}$ M$_{\odot} $), median $L(60\mu m) = 10^{9}$ L$_{\odot}$, median
dust temperatures of $ F60/F100 = 0.36 $, and median $L_{\textrm{H}\alpha}$
surface density of $ 10^{40.2} $ erg s$ ^{-1} $kpc$ ^{-2} $, indicating older
stellar populations as their main ionizing source rather than AGN activity.
