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1. The Diffuse Ionized Gas Halo of the Small Magellanic Cloud

   https://doi.org/10.3847/1538-4357/ab4d58  

   Smart, B. M. ; Haffner, L. M. ; Barger, K. A. ; Hill, A. ; Madsen, G. ( December 2019 , The Astrophysical Journal)

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2. Radiative transfer calculations of the diffuse ionized gas in disc galaxies with cosmic ray feedback

   https://doi.org/10.1093/mnras/sty554  

   Vandenbroucke, Bert ; Wood, Kenneth ; Girichidis, Philipp ; Hill, Alex S ; Peters, Thomas ( March 2018 , Monthly Notices of the Royal Astronomical Society)
3. The GBT Diffuse Ionized Gas Survey (GDIGS): Discrete Sources

   Matteo Luisi, Dylan Linville ( January 2023 , Bulletin of the AAS)

   The Green Bank Telescope (GBT) Diffuse Ionized Gas Survey (GDIGS) traces ionized gas in the Galactic midplane by observing radio recombination line (RRL) emission from 4–8 GHz. The nominal survey zone is 32.3° > l > -5°, |b| < 0.5°. Here, we analyze GDIGS Hnα ionized gas emission toward discrete sources with sizes comparable to the 2.065' GDIGS Hnα beam. We use GDIGS data to identify the correct velocity of 39 H II regions that have multiple RRL velocity components. We identify and characterize RRL emission from 88 H II regions that previously lacked measured ionized gas velocities. We additionally identify and characterize RRL emission from eight locations that appear to be previously-unidentified H II regions and 41 locations of RRL emission that do not appear to be H II regions based on their lack of mid-infrared emission. We identify 10 discrete sources that have anomalously high RRL velocities for their locations in the Galactic plane and we compare the objects’ RRL data to 13CO, H I and mid-infrared data. These sources do not have the expected 24 μm emission characteristic of H II regions. Based on this comparison we do not think these objects are H II regions, but we are unable to classify them as a known type of object. 

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4. The GBT Diffuse Ionized Gas Survey (GDIGS): Survey Overview and First Data Release

   https://doi.org/10.3847/1538-4365/abef65  

   Anderson, L. D. ; Luisi, Matteo ; Liu, Bin ; Wenger, Trey V. ; Balser, Dana. S. ; Bania, T. M. ; Haffner, L. M. ; Linville, Dylan J. ; Mascoop, J. L. ( May 2021 , The Astrophysical Journal Supplement Series)

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5. The Green Bank Telescope Diffuse Ionized Gas Survey (GDIGS)

   Rao, M. ; Wenger, T. V. ; Balser, D. S. ; Anderson, L. D. ; Armentrout, W. P. ; Bania, T. M. ; Budaiev, N. ; Haffner, L. M. ; Liu, B. ; Luisi, M. ( January 2020 , American Astronomical Society meeting #235)

   The Warm Ionized Medium (WIM) is a low density, diffuse ionized component of the Milky Way. The WIM is the last major component of the interstellar medium to be studied at high spatial and spectral resolution, and therefore many of its fundamental properties are not clear. Radiation from massive, OB-type stars, which live in the inner galaxy, is thought to escape discrete HII regions to ionize the WIM. However, the inner Galaxy has not been well studied due to extinction from dust at optical wavelengths. GDIGS is a fully-sampled Radio Recombination Line (RRL) survey of the inner Galactic Plane at C-band (4-8 GHz). RRL emission is not affected by extinction from dust, and GDIGS has sufficient spatial resolution to distinguish between HII regions and the WIM emission. Here we discuss the status of GDIGS and some preliminary results from the spectral analysis of the RRLs. 

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