Warm Ionized Medium Throughout the Sagittarius-Carina Arm
  Wisconsin H-Alpha Mapper (WHAM) observations of H-Alpha and [S
II]$\lambda6716$ emission are used to trace the vertical distribution and
physical conditions of the warm ionized medium (WIM) along the
Sagittarius-Carina arm. CO emission, tracing cold molecular gas in the plane of
the Galaxy, is used as a guide to isolate H-Alpha and [S II] emission along
individual spiral arms. Exponential scale heights of electron density squared
(or emission measure) are determined using H-Alpha emission above (below) the
midplane to be $330 \pm 80$ pc ( $550 \pm 230$ pc) along the near Sagittarius
arm, $300 \pm 100$ pc ($250 \pm 30$ pc) along the near Carina arm, and $>1000$
pc along the far Carina arm. The emission measure scale height tends to
increase as a function of Galactocentric radius along the Sagittarius-Carina
arm for $R_G > 8$ kpc. Physical conditions of the ionized gas are analyzed
using the [S II]/H-Alpha line ratio, which more closely traces H-Alpha
Intensity than height above the plane, z, suggesting a stronger relationship
with the in-situ electron density. We interpret this result as further evidence
for the majority of the observed diffuse emission originating from in-situ
ionized gas as opposed to scattered light from classical H II regions in the
plane.
