Carbon recombination lines near 327 MHz I. "Diffuse" CII regions in the Galactic Disk

In earlier papers (Roshi & Anantharamaiah 2000, 2001a), we presented extensive surveys (angular resolution - 2 2 and 2 6 0 ) of radio recombination lines (RRLs) near 327 MHz in the longitude range l = 332 ! 89 using the Ooty Radio Telescope. These surveys have detected carbon lines mostly between l = 358! 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 "diuse" Cii regions. The l-v diagram and radial distribution constructed from our carbon line data shows similarity with that obtained from hydrogen recombination lines at 3 cm from Hii regions indicating that the distribution of the diuse Cii regions in the inner Galaxy resembles the distribution of the star-forming regions. We estimated the (Cii) 158m emission from diuse Cii regions and find that upto 95% of the total observed (Cii) 158m emission can arise in diuse Cii regions if the temperature of the latter80 K. Our high-resolution survey data shows that the carbon line emitting regions have structures on angular scale 6 0 . Analysis of the dual-resolution observations toward a 2 wide field centered at l= 13:9 and toward the longitude range l= 1:75 to 6:75 shows the presence of narrow (V 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 diuse Cii region in these directions is>200 pc.