Ammonia observations towards molecular and optical outflows

We observed the (J,K) = (1,1) and (J,K) = (2,2) inversion transitions of the NH_3 molecule towards several regions with molecular or optical outflows: RNO 43, HH 83, HH 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 $6<SUB>16</SUB>-5<SUB>23</SUB>$ H<SUB>2</SUB>O maser line towards nine regions, detecting a weak H<SUB>2</SUB>O maser near IRAS 20188+3928. We detected and mapped NH_3 emission in 14 of the 15 regions observed, and we estimated physical parameters for the high density gas. We systematically found that the position of the best candidate for the outflow excitation in each region is very close to an NH_3 emission peak. From a statistical study of the data presented in this paper, 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 outflows appear to be associated with larger amounts of high density gas. This result suggests a possible evolutive scheme in which young objects associated with molecular outflows lose progressively their neighboring high-density gas, weakening both the NH_3 emission and the molecular outflow in the process, and making optical jets more easily detectable as the total amount of gas decreases.