A String of Radio Emission Associated with IRAS 16562-3959: A Collimated Jet Emanating from a Luminous Massive YSO

Abstract

We report the discovery made using the Australia Telescope Compact Array of a remarkable string of radio emission towards IRAS 16562-3959, a luminous infrared source with a bolometric luminosity of $7.0\times10^4$ \Lsun. The radio emission arises from a compact, bright central component, two inner lobes, which are separated by about 7\arcsec\ and symmetrically offset from the central source, and two outer lobes which are separated by about 45\arcsec. The emission from the central object has a spectral index between 1.4 and 8.6 GHz of $0.85\pm0.15$, consistent with free-free emission from a thermal jet. The radio emission from the lobes have spectral indices in the range characteristic of thermal emission. We suggest that the emission from the lobes arises in shocks resulting from the interaction of a collimated wind with the surrounding medium. The radio string is located within a massive dense molecular core, and is associated with extended green emission (Spitzer 3-color), Herbig-Haro type emission (2MASS K$_s$-band) and OH maser sites -- all phenomena readily observed towards sites of massive star formation. We conclude that the massive core hosts a high-mass star in an early stage of evolution in which it is undergoing the ejection of a powerful collimated stellar wind, showing that jets found in the formation of low-mass stars are also produced in high-mass stars.