GBT17B-173

The GBT Diffuse Ionized Gas Survey (GDIGS)

Abstract

Diffuse ionized gas in the mid-plane known as the "Warm Ionized Medium" (WIM) makes up ~20% of the Milky Way gas mass and >90% of its ionized gas. It is the last major component of the interstellar medium (ISM) to be studied at high spatial and spectral resolution, and therefore many of its fundamental properties remain unclear. We propose a filler project to map the WIM distribution from 32deg.>l>-5deg., |b|<0.5deg., using C-band recombination line measurements. We will simultaneously observe 22 Hn-alpha lines, 25 Hn-beta lines, 8 Hn-gamma lines, and 9 molecular lines (namely CH3OH and H2CO), and produce continuum maps at ~60 frequencies. We will average the Hn-alpha lines to produce Nyquist-sampled maps with rms sensitivities of ~1mJy per beam. We have observed ~15 square degrees so far and have a data reduction pipeline in place. These data will allow us to: 1) Study for the first time the inner-Galaxy WIM unaffected by confusion from discrete HII regions, 2) provide a census of the ionized gas in spiral arms, 3) investigate the ionization state of the WIM, 4) explore the WIM/HII region connection, and 5) analyze the effect of leaked photons from HII regions on ISM dust temperatures.

Investigators

Name	Institution
GBT Operator	Green Bank Observatory
Matteo Luisi	Westminster College
Loren Anderson *	West Virginia University
Bin Liu	West Virginia University; National Astronomical Observatories, CAS
Tom Bania	Boston University
Trey Wenger	Wisconsin at Madison, University of
Lawrence Haffner	Wisconsin at Madison, University of; Space Science Institute
Dana Balser	National Radio Astronomy Observatory

* indicates the PI