Detection of highly-ionized diffuse gas in the Galactic plane

Free access article

Issue		A&A Volume 382, Number 2, February I 2002


Page(s)		610 - 623
Section		Diffuse matter in space
DOI		http://dx.doi.org/10.1051/0004-6361:20011611

A&A 382, 610-623 (2002)
DOI: 10.1051/0004-6361:20011611

Detection of highly-ionized diffuse gas in the Galactic plane

M. Mizutani¹, T. Onaka¹ and H. Shibai²

¹ Department of Astronomy, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan
² Department of Physics, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan

(Received 1 September 2000 / Accepted 5 November 2001 )

Abstract
We obtained maps of the central $40\arcmin \times 20\arcmin$ region of the Carina nebula , an active star forming region in the southern Milky Way, in various emission lines in the spectral range 43-197 $\mu$ m with the LWS on board the ISO. This paper reports on the results of [ $\ion{O}{iii}$ ] 52, 88 $\mu$ m, [ $\ion{N}{iii}$ ] 57 $\mu$ m, and [ $\ion{N}{ii}$ ] 122 $\mu$ m lines. These ionized lines have been detected in the entire observed area, not only in the optically bright $\ion{H}{ii}$ region, but also in the molecular cloud direction and the region surrounding the Carina nebula. The electron density was derived from the [ $\ion{O}{iii}$ ] lines and two distinct components were seen in the electron density map. One is a component with a density of 100-350 cm ^-3, which encloses two $\ion{H}{ii}$ regions, Car I and Car II . The other is an extended diffuse component, in which the ratio of the [ $\ion{O}{iii}$ ] lines is nearly at the low electron density limit ( $n_{\rm e} < 100$ cm ^-3). The observed [ $\ion{N}{iii}$ ]/[ $\ion{O}{iii}$ ] line intensity ratio also supports low electron density of the extended gas component. The diffuse component was detected in the entire observed region, which corresponds to ~30 pc at the distance of the Carina nebula. The present LWS observations of the ionic lines indicate the existence of highly-ionized diffuse gas of low electron density extending around the Carina nebula.

Key words: infrared: ISM: lines and bands -- $\ion{H}{ii}$ regions -- ISM: individual objects: Carina nebula

Offprint request: T. Onaka, onaka@astron.s.u-tokyo.ac.jp

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