A search for the 53-MHz OH line near G48.4-1.4 using the National MST Radar Facility

Abstract

We present the results of a search for the ground-state hyperfine transition of the OH radical near 53 MHz using the National Mesosphere-Stratosphere-Troposphere (MST) Radar Facility at Gadanki, India. The observed position was G48.4-1.4 near the Galactic plane. The OH line is not detected. We place a 3σ upper limit for the line flux density at 39 Jy from our observations. We also did not detect recombination lines (RLs) of carbon, which were within the frequency range of our observations. The 3σ upper limit of 20 Jy obtained for the flux density of carbon RLs, along with observations at 34.5 and 327 MHz, are used to constrain the physical properties of the line-forming region. Our upper limit is consistent with the line emission expected from a partially ionized region with electron temperature, density and path lengths in the range 20-300 K, 0.03-0.3 cm-3 and 0.1-170 pc, respectively.