EDP Sciences
Free access
Volume 391, Number 3, September I 2002
Page(s) 1097 - 1113
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20020899

A&A 391, 1097-1113 (2002)
DOI: 10.1051/0004-6361:20020899

Carbon recombination lines near 327 MHz

I. "Diffuse" $\ion{C}{II}$ regions in the Galactic Disk
D. Anish Roshi1, 2, N. G. Kantharia2 and K. R. Anantharamaiah3

1  National Radio Astronomy Observatory, Green Bank, WV 24944, USA (The National Radio Astronomy Observatory is operated by associated Universities, Inc., under agreement with the National Science Foundation.)
2  National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune, India
3  Raman Research Institute, Bangalore, India

(Received 30 January 2002 / Accepted 13 June 2002 )

In earlier papers (Roshi & Anantharamaiah 2000, 2001a), we presented extensive surveys (angular resolution - 2°  $\times$ 2° and 2° $\times$ 6´) of radio recombination lines (RRLs) near 327 MHz in the longitude range l = 332° $\rightarrow$ 89° using the Ooty Radio Telescope. These surveys have detected carbon lines mostly between l = 358° $\rightarrow$ 20° and in a few positions at other longitudes. This paper presents the observed carbon line parameters in the high-resolution survey and a study of the galactic distribution and angular extent of the line emission observed in the surveys. The carbon lines detected in the surveys arise in "diffuse"  regions. The  diagram and radial distribution constructed from our carbon line data shows similarity with that obtained from hydrogen recombination lines at 3 cm from regions indicating that the distribution of the diffuse  regions in the inner Galaxy resembles the distribution of the star-forming regions. We estimated the ]  158  $\mu$m emission from diffuse  regions and find that upto 95% of the total observed ]  158  $\mu$m emission can arise in diffuse  regions if the temperature of the latter ~80 K. Our high-resolution survey data shows that the carbon line emitting regions have structures on angular scale ~6´. Analysis of the dual-resolution observations toward a 2° wide field centered at l = 13 $\fdg$9 and toward the longitude range l = 1 $\fdg$75 to 6 $\fdg$75 shows the presence of narrow ( $\Delta V \le $ 15 km s -1) carbon line emitting regions extending over several degrees in l and b. The physical size perpendicular to the line-of-sight of an individual diffuse  region in these directions is >200 pc.

Key words: Galaxy: general -- ISM: general -- ISM: structure -- radio lines: ISM -- infrared: ISM

Offprint request: D. Anish Roshi, aroshi@nrao.edu

© ESO 2002