2017MNRAS.471.4910R

We consider a conical jet from a massive, young star, which also powers a compact H II region. The high density at the base of the jet traps the stellar, ionizing radiation, so that the jet beam is neutral (at larger distances). This neutral beam then becomes progressively photoionized by the diffuse, ionizing radiation field emitted by the surrounding H II region. We derive a simple, analytic model for this flow, and use it to calculate the contrast between the free-free emission of the jet and the background H II region. We find that for appropriate parameters, the jet is brighter by ∼20 per cent, which should be relatively straightforward to detect in interferometric maps of regions around massive, young stars.