Hydrogen and carbon recombination lines towards the galactic centre near 328 MHz

Abstract

We present observations of the H271-alpha and the C271-alpha recombination lines from nine positions around the Galactic Center region made using the Ooty Radio Telescope. Both lines were detected in emission in all the positions. In the integrated spectrum obtained by averaging over all the nine positions, the H271-alpha line shows a narrow (8 km/s) component superposed on a previously known broad (38km/s) component. Further observations are required to confirm the narrow feature. The C271-alpha line near 328 MHz appears to be the emission counterpart of the absorption lines observed in this direction near 75 MHz by Erickson et al. The phenomenon of turnover from absorption to emission of low-frequency carbon recombination lines is similar to that observed in the direction of Cas A by Payne et al. using a model that incorporates the effects of dielectronic-like recombination in carbon, we show that the observed lines can be explained by a region with T(e) = 70-80 K, n(e) = 0.005-0.01/cu cm, and an effective pathlength of 200-500 pc.