The population of compact radio sources in M 17

TL;DR

This study catalogs 194 radio sources in M 17, revealing a high fraction of stellar coronal emission, comparing their properties with other regions, and identifying a potential protostellar disk near a hyper-compact source.

Contribution

It provides the first deep radio catalog of M 17, analyzes the nature of its sources, and compares their luminosity functions with other star-forming regions.

Findings

At least 40% of sources show suspected gyrosynchrotron emission.

Radio sources in M 17 are three times more numerous than in Orion at similar luminosities.

An arc-shaped ionizing front with a protostellar disk candidate was identified.

Abstract

We present a catalog of radio sources of the M 17 region based on deep X band radio observations centered at 10 GHz obtained with the Jansky Very Large Array in the A configuration. We detect a total of 194 radio sources, 12 of them extended and 182 compact. We find that a significant fraction (at least 40% in our catalog) have suspected gyrosynchrotron emission associated with stellar coronal emission. By comparing the radio luminosities of our sources with their X ray counterparts, when available, we find that they are underluminous in X rays with respect to the G\"udel Benz relation, but a correlation with a similar slope is obtained provided that only sources with evident non thermal nature are selected from the sample compiled for the Orion Nebula Cluster (ONC) and M 17. The comparison of M 17 with the ONC and NGC 6334D-F leads to a similar luminosity function for the three regions, at least for the more luminous sources. However, the radio sources in M 17 are three times more numerous compared to the other regions at a given luminosity and their spatial distribution differs from that of Orion. Moreover, an arc-shaped structure of 40$"$ in extent is observed in our map, identified previously as an ionizing front, with the cometary Hyper Compact source UC1 at its focus. Archival 1 mm ALMA data reveals compact emission coincident with the radio wavelength peak, possibly associated with a protostellar disk of the massive star exciting UC1.