An ionized outflow in Orion-KL source I?

TL;DR

This study presents multi-frequency radio observations of Orion-KL Source I, revealing an ionized outflow aligned with the bipolar SiO outflow, supporting a broad disk wind rather than a narrow jet.

Contribution

It provides new evidence for an ionized outflow in Source I, favoring a broad disk wind model over a narrow jet based on multi-frequency radio imaging.

Findings

Detection of elongated emission aligned with the SiO bipolar outflow.

Flux and size variations with frequency consistent with free-free emission from an ionized outflow.

Non-detection at 5 GHz in high-resolution observations suggests possible resolution effects or variability.

Abstract

We present images at 6 and 14 GHz of Source I in Orion-KL. At higher frequencies, from 43 to 340 GHz, images of this source are dominated by thermal emission from dust in a 100 AU diameter circumstellar disk, but at 6 and 14 GHz the emission is elongated along the minor axis of the disk, aligned with the SiO bipolar outflow from the central object. Gaussian fits to the 6, 14, 43, and 99 GHz images find a component along the disk minor axis whose flux and length vary with frequency consistent with free-free emission from an ionized outflow. The data favor a broad outflow from a disk wind, rather than a narrow ionized jet. Source I was undetected in higher resolution 5 GHz e-MERLIN observations obtained in 2021. The 5-6 GHz structure of SrcI may be resolved out by the high sidelobe structure of the e-MERLIN synthesized beam, or be time variable.