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Astron. Astrophys. 319, 788-795 (1997)

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H detection of a clump of distant HII regions in the Milky Way *

D. Russeil

Observatoire de Marseille, 2 Place Le Verrier, F-13248 Marseille Cedex 04, France

Received 9 February 1996 / Accepted 5 September 1996


A group of 8 HII regions has been detected at a distance of 10 kpc from the Sun at galactic longitude [FORMULA], using H [FORMULA] wavelength observations. The observations were made with a scanning Fabry-Perot interferometer to provide a detailed H [FORMULA] profile, which enables us to separate these distant HII regions from the 3 other layers of ionized gas seen along the line of sight. A comparison of 5 GHz continuum and IRAS data allows us to analyse the nature of each source. Most of the distant HII regions were already known as radio sources or IRAS sources but one of them has no radio or IRAS counterpart. Inversely, IRAS sources without radio continuum nor an H [FORMULA] counterpart have been detected. Closer to us, on the same line of sight, we detected diffuse H [FORMULA] emission linking the Sagittarius arm with the Carina arm at a distance of about 2.5 kpc, where no usual tracer of spiral structure had previously been found. The HII region RCW 64, also seen in this direction, seems to be located between the two main spiral arms.

Key words: interstellar medium: HII regions – Galaxy: structure – infrared: ISM: continuum – radio continuum

* Based on observations collected at the European Southern Observatory

Send offprint requests to: D. Russeil

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998