The EDGE-CALIFA Survey: Evidence for Pervasive Extraplanar Diffuse
  Ionized Gas in Nearby Edge-On Galaxies
  We investigate the prevalence, properties, and kinematics of extraplanar
diffuse ionized gas (eDIG) in a sample of 25 edge-on galaxies selected from the
CALIFA survey. We measure ionized gas scale heights from ${\rm H\alpha}$ and
find that 90% have measurable scale heights with a median of
$0.8^{+0.7}_{-0.4}$ kpc. From the ${\rm H\alpha}$ kinematics, we find that 60%
of galaxies show a decrease in the rotation velocity as a function of height
above the midplane. This lag is characteristic of eDIG, and we measure a median
lag of 21 km s$^{-1}$ kpc$^{-1}$ which is comparable to lags measured in the
literature. We also investigate variations in the lag with radius. $\rm
H{\small I}$ lags have been reported to systematically decrease with
galactocentric radius. We find both increasing and decreasing ionized gas lags
with radius, as well as a large number of galaxies consistent with no radial
lag variation, and investigate these results in the context of internal and
external origins for the lagging ionized gas. We confirm that the ${\rm
[S{\small II}]}$/${\rm H\alpha}$ and ${\rm [N{\small II}]}$/${\rm H\alpha}$
line ratios increase with height above the midplane as is characteristic of
eDIG. The ionization of the eDIG is dominated by star-forming complexes (leaky
${\rm H{\small II}}$ regions). We conclude that the lagging ionized gas is
turbulent ejected gas likely resulting from star formation activity in the disk
as opposed to gas in the stellar thick disk or bulge. This is further evidence
for the eDIG being a product of stellar feedback and for the pervasiveness of
this WIM-like phase in many local star-forming galaxies.
