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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