SDSS IV MaNGA: Deep observations of extra-planar, diffuse ionized gas
  around late-type galaxies from stacked IFU spectra
  We have conducted a study of extra-planar diffuse ionized gas using the first
year data from the MaNGA IFU survey. We have stacked spectra from 49 edge-on,
late-type galaxies as a function of distance from the midplane of the galaxy.
With this technique we can detect the bright emission lines Halpha, Hbeta,
[OII]3726, 3729, [OIII]5007, [NII]6549, 6584, and [SII]6717, 6731 out to about
4 kpc above the midplane. With 16 galaxies we can extend this analysis out to
about 9 kpc, i.e. a distance of ~2R_e, vertically from the midplane. In the
halo, the surface brightnesses of the [OII] and Halpha emission lines are
comparable, unlike in the disk where Halpha dominates. When we split the sample
by specific star formation rate, concentration index, and stellar mass, each
subsample's emission line surface brightness profiles and ratios differ,
indicating that extra-planar gas properties can vary. The emission line surface
brightnesses of the gas around high specific star formation rate galaxies are
higher at all distances, and the line ratios are closer to ratios
characteristic of HII regions compared with low specific star formation rate
galaxies. The less concentrated and lower stellar mass samples exhibit line
ratios that are more like HII regions at larger distances than their more
concentrated and higher stellar mass counterparts. The largest difference
between different subsamples occurs when the galaxies are split by stellar
mass. We additionally infer that gas far from the midplane in more massive
galaxies has the highest temperatures and steepest radial temperature gradients
based on their [NII]/Halpha and [OII]/Halpha ratios between the disk and the
halo.
