OBSERVATIONS OF THE J=1-0 TRANSITION OF HCO+ IN SOUTHERN MOLECULAR CLOUDS

The /= 1—0 transition of HCO+ at 89 GHz has been detected with the 4-m Epping radio telescope at 42 positions out of a total sample of 55 associated with dense molecular clouds (mostly with southern declinations). The telescope beamwidth was 3.3 arcmin and the sensitivity limit was 0.5—0.75 K in 'corrected antenna temperature'. The lower limit for the typical HCO+ column density, based on assumptions of low optical depth and an excitation temperature of 15 K, is 3 x 1013 cm2. The velocities of the HCO+ emission are similar to those of ground-state transitions of CO, CS, HCN; there is also a strong correlation between the HCO+ and HCN profile areas. Extensive HCO+ emission has been observed in the Galactic Centre region, associated with a dense molecular cloud complex in the nuclear disc. Faint HCO+ emission is present in N159 in the Large Magellanic Cloud and possibly inNGC5128. © Royal Astronomical Society.