Probing the centre of the large circumstellar disc in M 17★

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 JHK s L' M'-band imaging carried out with Nasmyth Adaptive Optics System/Coude Near Infrared Camera (NAOS/CONICA) at the Very Large Telescope (VLT) with [Fe n] narrow-band imaging using SOFI [Son of ISAAC (Infrared Spectrograph and Array Camera)] at the New Technology Telescope (NTT). The analysis is supported by Spitzer/GLIMPSE archival data and by already published Spectrograph for Integral Field Observations in the Near Infrared (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 H 2 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 ≤ A v < 82. The observed K s -band magnitude is equivalent to a stellar mass range of 2.8 M ⊙ ≤ M * ≤ 8 M ⊙ 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.