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20th of May 2015
The HIPASS survey of the Galactic plane in radio recombination lines
by Marta Alves (IRAP, Toulouse)
Radio recombination line (RRL) observations have been widely used to probe the physical conditions of the ionised gas in the Milky Way. These studies have been restricted to individual HII regions and discrete lines-of-sight away from strong continuum sources - to probe the diffuse ionised gas. The HI Parkes All-Sky Survey (HIPASS), which focused on detecting HI emission from galaxies, happens to contain three hydrogen RRLs in its passband: H168α, H167α, and H166α. We re-analised the HIPASS (and the associated Zone of Avoidance) dataset to extract and combine these three lines, and to derive fully sampled maps of the diffuse ionised emission in the region of longitude l = 196 - 0 - 52 deg and latitude |b| < 5 deg (as shown in the figure above). This is the first contiguous survey of RRL emission in the plane of the Galaxy. The data reduction and analysis is described in Alves et al. (2015, MNRAS 450, 2025) and the data products are available for download.

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