GBT22B-327

SIP: Probing the Warm Ionized Medium toward the Outer Galaxy

Abstract

The Warm Ionized Medium (WIM) consists of diffuse ionized gas in the
Galactic mid-plane and is the last major component of the interstellar
medium to be studied at high spatial and spectral resolution.
Recently, we completed the GBT Diffuse Ionized Gas Survey (GDIGS) to
map the hydrogen radio recombination line (RRL) WIM emission at
C-band, from l = -5 to 32 degrees and |b| < 0.5 degrees. We average
the Hn-alpha lines to produce Nyquist-sampled maps with a spatial
resolution of 2 arcmin and rms sensitivities of ~ few mK. We detect
hydrogen RRL emission at nearly all positions and can connect this WIM
emission to the halos of discrete HII regions. We do not detect RRL
emission at all expected velocities, however, which may indicate a
lack of WIM along the line-of-sight or, more likely, a sensitivity
issue. More sensitive RRL observations near l = 20 degrees indicate
pervasive ionized gas inside the Solar orbit, but no emission outside
the Solar orbit. Here we propose sensitive observations at l = 180
degrees, where velocity crowding will increase our sensitivity, to
produce a canonical value of the emission measure in the Outer Galaxy.

Investigators

Name	Institution
GBT Operator	Green Bank Observatory
Dana Balser *	National Radio Astronomy Observatory
Tom Bania	Boston University
Spencer Ireland	Boston University
Matteo Luisi	Westminster College
William Armentrout	Green Bank Observatory
Trey Wenger	Wisconsin at Madison, University of
Loren Anderson	West Virginia University

* indicates the PI