From downtown to the outskirts: a radio survey of the Orion Nebula Cluster

TL;DR

This study expands the radio source catalog of the Orion Nebula Cluster using high-sensitivity VLA observations, revealing new sources, proper motions, and variability, and exploring the relationship between radio and X-ray emissions.

Contribution

It provides the largest radio survey of the ONC to date, identifying new sources, proper motions, and variability, and analyzing their relation to X-ray counterparts and cluster environment.

Findings

521 compact radio sources detected, 198 new

Higher radio detection fraction of X-ray sources in the inner cluster

Discovery of fast proper motions up to 373 km/s

Abstract

We present a newly enlarged census of the compact radio population towards the Orion Nebula Cluster (ONC) using high-sensitivity continuum maps (3-10 $\mu$Jy bm$^{-1}$) from a total of $\sim30$ h centimeter-wavelength observations over an area of $\sim$20$'\times20'$ obtained in the C-band (4$-$8 GHz) with the Karl G. Jansky Very Large Array (VLA) in its high-resolution A-configuration. We thus complement our previous deep survey of the innermost areas of the ONC, now covering the field of view of the Chandra Orion Ultra-deep Project (COUP). Our catalog contains 521 compact radio sources of which 198 are new detections. Overall, we find that 17% of the (mostly stellar) COUP sources have radio counterparts, while 53% of the radio sources have COUP counterparts. Most notably, the radio detection fraction of X-ray sources is higher in the inner cluster and almost constant for $r>3'$ (0.36 pc) from $\theta^1$ Ori C suggesting a correlation between the radio emission mechanism of these sources and their distance from the most massive stars at the center of the cluster, for example due to increased photoionisation of circumstellar disks. The combination with our previous observations four years prior lead to the discovery of fast proper motions of up to $\sim$373 km s$^{-1}$ from faint radio sources associated with ejecta of the OMC1 explosion. Finally, we search for strong radio variability. We found changes in flux density by a factor of $\lesssim$5 within our observations and a few sources with changes by a factor $>$10 on long timescales of a few years.