Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21832105a&link_type=abstract
American Astronomical Society, AAS Meeting #218, #321.05; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
We report, for the first time, that the low frequency carbon recombination lines (CRRLs) from the innermost ˜ 10° of the Galaxy arise in the Heeschan-Riegel-Crutcher (HRC) cloud. The HRC cloud is amongst the most well known of HI self-absorbing (HISA) regions located at a distance of about 125 pc in the Galactic centre direction. We demonstrate that the physical properties of the HISA can be constrained by combining multi-frequency CRRL and HI observations.The derived physical properties of the HISA cloud are used to determine the cooling and heating rates. The dominant cooling process is emission of the CII 158 µm line whereas dominant heating process in the cloud interior is photoelectric emission. Constraints on the FUV flux (G0 ˜ 4 to 7) falling on the HRC cloud are obtained by assuming thermal balance between the dominant heating and cooling processes. The H_2 formation rate per unit volume in the cloud interior is ˜ 10^{-10} -- 10^{-12} s^{-1} cm^{-3}, which far exceeds the H_2 dissociation rate per unit volume. We conclude that the self-absorbing cold HI gas in the HRC cloud may be in the process of converting to the molecular form. The cold HI gas observed as HISA features are ubiquitous in the inner Galaxy and form an important part of the ISM. Our analysis shows that combining CRRL and HI data can give valuable insight into the nature of these cold gas. We also present results from new low-frequency (< 800 MHz) CRRL observations toward HRC cloud using the Green Bank Telescope.
Anish Roshi D.
Kantharia Nimisha G.
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