Abstract
We present a comprehensive study of the interstellar NaI $łambda$5890, 5895
(NaD) resonant lines in a complete spectroscopic sample of $600,000$
passive, star-forming and starburst galaxies drawn from SDSS DR7 in order to
look for cold-gas outflows in the local Universe. Individual galaxy spectra are
stacked in bins of stellar mass and SFR and the dependence of galactic winds,
with respect to the galaxies position in the SFR-$M_\star$ plane is
investigated. While in most cases the interstellar medium (ISM) lines are fixed
at the galaxy systemic velocity, at the higher SFR tail (SFR$>12.5 M_ødot
yr^-1$), we find evidence of blue-shifted NaD absorption profiles, which we
interpret as evidence of neutral outflowing gas. We explore the properties of
the ISM in these galaxies with high SFR, in particular relating the absorption
NaD line shape with the galaxy geometry in galaxies with different ionization
mechanisms: AGN and star-formation. We find that: a) the ISM NaD absorption
lines show a clear transition from a strong disk-like component, perfectly
centered to the systemic velocity, in the edge-on system ($i > 50^\circ$ of the
disk rotation axis), to an outflow, blue-shifted, component in face-on galaxies
($i < 50^\circ$); b) these trends are observed in galaxies classified as
"purely" SF and AGN dominated objects. We compare the kinematics of the neutral
gas with the kinematics of the ionized gas as traced by the OIII$łambda$5007
emission lines. We find that, in these high SFR galaxies, the perturbations of
the OIII emission line are present only in AGN or composite systems. 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 star formation rate along the galaxy disk
and the ionized winds related to the AGN feedback.
Description
[1710.08423] Two-Face(s): ionized and neutral gas winds in the local Universe
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