A Jet-like Outflow toward the High-Mass (Proto)stellar Object IRAS 18566+0408
Abstract
We performed interferometric observations of a high-mass protostellar candidate IRAS 18566+0408 in the 3 (J,K)=(1,1), (2,2) and (3,3) inversion transitions, the SiO J=2-1 and HCN J=1-0 lines, and the 43 and 87 GHz continuum emission using the VLA and OVRO. The 87 GHz continuum emission reveals two continuum peaks MM-1 and MM-2 along a molecular ridge. The dominant peak MM-1 coincides with a compact emission feature at 43 GHz, and arises mostly from the dust emission. For dust emissivity index β of 1.3, the masses in the dust peaks amount to 70 for MM-1, and 27 for MM-2. Assuming internal heating, the central luminosities of MM-1 and MM-2 are 6 × 104 and 8 × 103 , respectively. The SiO emission reveals a well collimated outflow emanating from MM-1. The jet-like outflow is also detected in 3 at velocities similar to the SiO emission. The outflow, with a mass of 27 , causes significant heating in the gas to temperatures of 70 K, much higher than the temperature of 15 K in the extended core. Compact (< 3'') and narrow line (<1.5 -1) 3 (3,3) emission features are found associated with the outflow. They likely arise from weak population inversion in 3 similar to the maser emission. Toward MM-1, there is a compact 3 structure with a linewidth that increases from 5.5 -1 FHWM measured at 3'' resolution to 8.7 -1\ measured at 1'' resolution. This linewidth is much larger than the FWHM of < 2 -1 in the entire core, and does not appear to originate from the outflow. This large linewidth may arise from rotation/infall, or relative motions of unresolved protostellar cores.