A Jet-like Outflow toward the High-Mass (Proto)stellar Object IRAS 18566+0408

We performed interferometric observations of a high-mass protostellar candidate IRAS 18566+0408 in the \nh3 (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 $\beta$ of 1.3, the masses in the dust peaks amount to 70 \msun for MM-1, and 27 \msun for MM-2. Assuming internal heating, the central luminosities of MM-1 and MM-2 are $6\times {10}^4$ and $8 \times 10^3$ \lsun, respectively. The SiO emission reveals a well collimated outflow emanating from MM-1. The jet-like outflow is also detected in \nh3 at velocities similar to the SiO emission. The outflow, with a mass of 27 \msun, causes significant heating in the gas to temperatures of 70 K, much higher than the temperature of $\text{lsim}15$ K in the extended core. Compact ($<3^{\mathrm{\prime }\mathrm{\prime }}$) and narrow line ($<1.5$ \kms-1) \nh3 (3,3) emission features are found associated with the outflow. They likely arise from weak population inversion in \nh3 similar to the maser emission. Toward MM-1, there is a compact \nh3 structure with a linewidth that increases from 5.5 \kms-1 FHWM measured at 3${}^{\mathrm{\prime }\mathrm{\prime }}$ resolution to 8.7 \kms-1
measured at 1${}^{\mathrm{\prime }\mathrm{\prime }}$ resolution. This linewidth is much larger than the FWHM of $<$ 2 \kms-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.