High-velocity sulfur monoxide emission from protostellar outflows

Abstract

We have mapped the JN = 23-12 and 65-54 transitions of SO and the J = 5-4 transition of SiO in nine regions containing protostellar molecular outflows. We find that, in general, the spatial pattern of the SO emission and shape of the line profiles is different for each transition. In the quiescent gas, the SO emission is widespread in the ambient clouds, but JN = 23-12 and JN = 32-21 emission is relatively weak in the warm, dense cores around the young stars, while the JN = 65-54 emission is found to be strongest in the cores. In the outflowing gas, the SO 65-54 line is detected toward the outer parts of the CO lobes and shows high-velocity (HV: 5-32 km/s) wings, while the SO JN = 32-21 and JN = 23-12 emission is not detected. SiO J = 5-4 shows similar HV emission to SO JN = 65-54 but little emission from the quiescent gas. In general, SO and SiO emission from the outflow does not resemble maps or line profiles of CO, CS, NH3, or HCO(+). These results give further support that lines of SO and SiO can be very useful as specific tracers of shocked gas in outflows. The observations presented here are not easily explained with the current shock models.