Astronomy and Astrophysics, volume 319, 788-795 (1997/3-3)
Hα detection of a clump of distant HII regions in the Milky Way.
Abstract (from CDS):
A group of 8 HII regions has been detected at a distance of 10kpc from the Sun at galactic longitude 298°, using Hα wavelength observations. The observations were made with a scanning Fabry-Perot interferometer to provide a detailed Hα 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 5GHz 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 Hα counterpart have been detected. Closer to us, on the same line of sight, we detected diffuse Hα emission linking the Sagittarius arm with the Carina arm at a distance of about 2.5kpc, 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.
interstellar medium: HII regions - Galaxy: structure - infrared: ISM: continuum - radio continuum