The HIPASS survey of the Galactic plane in Radio Recombination Lines

Marta I. R. Alves; Mark Calabretta; Rodney D. Davies; Clive Dickinson; Lister Staveley-Smith; Richard J. Davis; Tianyue Chen; Adam Barr

doi:10.1093/mnras/stv751

arXiv · 1411.4497

The HIPASS survey of the Galactic plane in Radio Recombination Lines

Marta I. R. Alves·Mark Calabretta·Rodney D. Davies·Clive Dickinson·Lister Staveley-Smith·Richard J. Davis·Tianyue Chen·Adam Barr

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Abstract

We present a Radio Recombination Line (RRL) survey of the Galactic Plane from the HI Parkes All-sky Survey and associated Zone of Avoidance survey, which mapped the region l=196degr -- 0degr --52degr and |b| < 5degr at 1.4 GHz and 14.4 arcmin resolution. We combine three RRLs, H168$\alpha$, H167$\alpha$, and H166$\alpha$ to derive fully sampled maps of the diffuse ionized emission along the inner Galactic plane. The velocity information, at a resolution of 20 km/s, allows us to study the spatial distribution of the ionized gas and compare it with that of the molecular gas, as traced by CO. The longitude-velocity diagram shows that the RRL emission is mostly associated with CO gas from the molecular ring and is concentrated within the inner 30degr of longitude. A map of the free-free emission in this region of the Galaxy is derived from the line-integrated RRL emission, assuming an electron temperature gradient with Galactocentric radius of $496\pm100$ K/kpc. Based on the thermal continuum map we extracted a catalogue of 317 compact (<15 arcmin) sources, with flux densities, sizes and velocities. We report the first RRL observations of the southern ionized lobe in the Galactic centre. The line profiles and velocities suggest that this degree-scale structure is in rotation. We also present new evidence of diffuse ionized gas in the 3-kpc arm. Helium and carbon RRLs are detected in this survey. The He line is mostly observed towards HII regions, whereas the C line is also detected further away from the source of ionization. These data represent the first observations of diffuse C RRLs in the Galactic plane at a frequency of 1.4 GHz.

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Marta I. R. Alves, Mark Calabretta, Rodney D. Davies, Clive Dickinson, Lister Staveley-Smith, Richard J. Davis, Tianyue Chen, Adam Barr. 2014-11-17. The HIPASS survey of the Galactic plane in Radio Recombination Lines. https://doi.org/10.1093/mnras/stv751

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