AMMONIA OBSERVATIONS TOWARDS MOLECULAR AND OPTICAL OUT FLOWS

We observed the (J, K) = (1, 1) and (J, K) = (2, 2) inversion transiti ons of the NH3 molecule towards several regions with molecular or opti cal outflows: RNO 43, HH 83, KH 84, HH 86/87/88, L1641-N, L100, L483, L673, IRAS 20188+3928, L1228, L1048, HHL 73, L1251 (IRAS 22343 + 7501 and IRAS 22376+7455) and L1262, using the 37 m radio telescope of the Haystack Observatory. Additionally, we searched for the 6(16) - 5(23) H2O maser line towards nine regions, detecting a weak H2O maser near I RAS 20188+3928. We detected and mapped NH3 emission in 14 of the 15 re gions observed, and we estimated physical parameters for the high dens ity gas. We systematically found that the position of the best candida te for the outflow excitation in each region is very close to an NH3 e mission peak. From a statistical study of the data presented in this p aper, together with previously published data, we conclude that the NH 3 line emission is more intense towards molecular outflow sources than towards sources with only optical outflows. Therefore, molecular outf lows appear to be associated with larger amounts of high density gas. This result suggests a possible evolutive scheme in which young object s associated with molecular outflows lose progressively their neighbor ing high-density gas, weakening both the NH3 emission and the molecula r outflow in the process, and making optical jets more easily detectab le as the total amount of gas decreases.