Absorption-line probes of the prevalence and properties of outflows in
  present-day star-forming galaxies
  We analyze star forming galaxies drawn from SDSS DR7 to show how the
interstellar medium (ISM) Na I 5890, 5896 (Na D) absorption lines depend on
galaxy physical properties, and to look for evidence of galactic winds. We
combine the spectra of galaxies with similar geometry/physical parameters to
create composite spectra with signal-to-noise ~300. The stellar continuum is
modeled using stellar population synthesis models, and the continuum-normalized
spectrum is fit with two Na I absorption components. We find that: (1) ISM Na D
absorption lines with equivalent widths EW > 0.8A are only prevalent in disk
galaxies with specific properties -- large extinction (Av), high star formation
rates (SFR), high star formation rate per unit area ($\Sigma_{\rm SFR}$), or
high stellar mass (M*). (2) the ISM Na D absorption lines can be separated into
two components: a quiescent disk-like component at the galaxy systemic velocity
and an outflow component; (3) the disk-like component is much stronger in the
edge-on systems, and the outflow component covers a wide angle but is stronger
within 60deg of the disk rotation axis; (4) the EW and covering factor of the
disk component correlate strongly with dust attenuation, highlighting the
importance that dust shielding may play the survival of Na I. (5) The EW of the
outflow component depends primarily on $\Sigma_{\rm SFR}$ and secondarily on
Av; (6) the outflow velocity varies from ~120 to 160km/s but shows little hint
of a correlation with galaxy physical properties over the modest dynamic range
that our sample probes (1.2 dex in log$\Sigma_{\rm SFR}$ and 1 dex in log M*).
