Probing the centre of the large circumstellar disc in M17

TL;DR

This study uses high-resolution infrared imaging and archival data to resolve the central emission in the M17 disc, revealing a protostar with a bipolar jet and surrounding nebulae, indicating ongoing high-mass star formation.

Contribution

First resolution of the central infrared emission into a protostar and jet features in M17's large circumstellar disc, linking the emission to active high-mass star formation.

Findings

Resolved the central emission into a protostar and jet-like feature.

Detected bipolar jets and nebulae at 1500 AU from the disc center.

Estimated the protostar's mass to be between 2.8 and 8 solar masses.

Abstract

We investigated the nature of the hitherto unresolved elliptical infrared emission in the centre of the ~20000 AU disc silhouette in M 17. We combined high-resolution JHKsL'M' band imaging carried out with NAOS/CONICA at the VLT with [Fe II] narrow band imaging using SOFI at the NTT. The analysis is supported by Spitzer/GLIMPSE archival data and by already published SINFONI/VLT Integral Field Spectroscopy data. For the first time, we resolve the elongated central infrared emission into a point-source and a jet-like feature that extends to the northeast in the opposite direction of the recently discovered collimated H2 jet. They are both orientated almost perpendicular to the disc plane. In addition, our images reveal a curved southwestern emission nebula whose morphology resembles that of the previously detected northeastern one. Both nebulae are located at a distance of 1500 AU from the disc centre. We describe the infrared point-source in terms of a protostar that is embedded in circumstellar material producing a visual extinction of 60 <= Av <= 82. The observed Ks band magnitude is equivalent to a stellar mass range of 2.8 Msun <= Mstar <= 8 Msun adopting conversions for a main-sequence star. Altogether, we suggest that the large M 17 accretion disc is forming an intermediate to high-mass protostar. Part of the accreted material is expelled through a symmetric bipolar jet/outflow.