Title:	Carbon recombination lines from the galactic plane at 34.5 & 328 MHz
Authors:	Kantharia, N.G. Anantharamaiah, K.R.
Keywords:	Interstellar medium: clouds, lines, line profiles, radio lines.
Issue Date:	2001
Publisher:	Indian Academy of Sciences, Bangalore, India.
Citation:	Journal of Astrophysics and Astronomy, 2001, Vol.22, p51-80.
Abstract:	We present the results of a search for carbon recombina- tion lines in the Galaxy at 34.5 MHz (C575α) made using the dipole array at Gauribidanur near Bangalore. Observations made towards 32 directions resulted in detections of lines in absorption at nine positions. Follow up observations at 328 MHz (C272α) using the Ooty Radio Telescope detected these lines in emission. A VLA D-array observation of one of the positions at 330 MHz yielded no detection implying a lower limit of 10' for the angular size of the line forming region. The longitude-velocity distribution of the observed carbon lines in- dicate that the line forming regions are located mainly between 4 kpc and 7 kpc from the Galactic centre. Combining our results with pub- lished carbon recombination line data near 76 MHz (Erickson, Mc- Connell& Anantharamaiah 1995), we obtain constraintson the physical parameters of the line forming regions. We find that if the angular size of the line forming regions is ≥ 4°, then the range of pararne- ters that fit the data are: Te = 20 - 40 K, ne ~ 0.1 - 0.3 cm-3and pathlengths ~ 0.07 - 0.9 pc which may correspond to thin photo- dissociated regions around molecular clouds. On the other hand, if the line forming regions are ~ 2° in extent, then warmer gas (Te ~ 60 - 300 K) with lower electron densities (ne ~ 0.03 - 0.05 cm-3 extending over several tens of parsecs along the line of sight and possibly associated with atomic HI gas can fit the data. Based on the range of derived parameters, we suggest that the carbon line regions are most likely associated with photo-dissociation regions.
URI:	http://hdl.handle.net/2289/811
ISSN:	0250-6335
Copyright:	Indian Academy of Sciences, Bangalore, India.
Appears in Collections:	Research Papers (A&A)

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