Two-Face(s): ionized and neutral gas winds in the local Universe
  We present a comprehensive study of the Na I $\lambda$5890, 5895 (Na I D)
resonant lines in the Sloan Digital Sky Survey (SDSS, DR7) spectroscopic sample
to look for neutral gas outflows in the local galaxies. Individual galaxy
spectra are stacked in bins of M${\star}$ and SFR to investigate the dependence
of galactic wind occurrence and velocity as a function of the galaxy position
in the SFR-$M{\star}$ plane. In massive galaxies at the high SFR tail we find
evidence of a significant blue-shifted Na I D absorption, which we interpret as
evidence of neutral outflowing gas. The occurrence of the blue-shifted
absorption is observed at the same significance for purely SF galaxies, AGN and
composite systems at fixed SFR. In all classes of objects the blue-shift is the
largest and the Na I D equivalent width the smallest for face-on galaxies while
the absorption feature is at the systemic velocity for edge-on systems. This
indicates that the neutral outflow is mostly perpendicular or biconical with
respect to the galactic disk. We also compare the kinematics of the neutral gas
with the ionized gas phase as traced by the [OIII]$\lambda$5007, H$\alpha$,
[NII]$\lambda6548$ and [NII]$\lambda6584$ emission lines. Differently for the
neutral gas phase, all the emission lines show evidence of perturbed kinematics
only in galaxies with a significant level of nuclear activity and, they are
independent from the disk inclination. In conclusion, we find that, in the
local Universe, galactic winds show two faces which are related to two
different ejection mechanisms, namely the neutral outflowing gas phase related
to the SF activity along the galaxy disk and the ionized phase related to the
AGN feedback. In both the neutral and ionized gas phases, the observed wind
velocities suggest that the outflowing gas remains bound to the galaxy with no
definitive effect on the gas reservoir.
