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9th of December 2021
GASKAP Pilot Survey observations of the Galactic plane
by Dickey et al.
Dickey et al. have used the Australian Square Kilometre Array Pathfinder to measure 21-cm absorption spectra toward continuum background sources, in order to study the cool phase of the neutral atomic gas in our Galaxy. The figures above show a comparison with spectra from the Southern Galactic Plane Survey (SGPS), undertaken with the ATCA and Parkes 64m telescope, Murriyang. The blue shading indicates the 1-sigma noise level in the SGPS data, which is typically larger than that of the GASKAP spectra by a factor of three to ten. The two panels are spectra toward bright continuum sources, so that discrepencies between the two surveys are due to emission fluctuations causing confusion that manifests as positive or negative “pseudo-absorption”. The GASKAP spectra are rich with absorption features at negative velocities, corresponding to structures in the cool neutral medium of the inner Galaxy. Particularly prominent is the line at a veolcity of −30 km/s that is due to cold clouds in the Scutum-Centaurus Arm at distance of ~2.8kpc from the solar system and at Galactocentric radius of ~5.8 kpc.

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