NRAO/Socorro Colloquium Series: 07 September 2001

Anish Roshi

NRAO
Greenbank, West Virginia


Low frequency carbon recombination lines towards HI self-absorption features in the Galaxy


Extensive surveys (angular resolution - 2 deg x 2 deg and 2 deg x 6 arcmin) of radio recombination lines (RRLs) at 327 MHz in the longitude range l = 332 deg to 89 deg were made with the Ooty Radio Telescope. These surveys detected carbon lines mostly between l = 358 deg to 20 deg and in a few positions at other longitudes. The carbon lines observed near 327 MHz originate from "diffuse" CII regions. We discuss the galactic distribution of "diffuse" CII regions and show that, in the inner Galaxy, the distribution is similar to that of spiral arm components.

Interestingly, towards several positions in the inner Galaxy, the central velocities of the observed carbon lines coincide with HI self-absorption features. HI self-absorption is observed when a cool (~20 K) HI cloud appears in absorption against HI emission from warmer gas behind it. The similarity of the central velocities suggests that the "diffuse" CII regions in these directions coexist with cool HI clouds. The observed width (~4 km/s) of the HI self-absorption features are, however, much narrower than the width (~17 km/s) of the carbon RRLs. We discuss possible explanations for the difference in the widths of line emission from the two species.






Friday, 07 September 2001
11:00am

Array Operations Center Auditorium

Local Host: Miller Goss


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