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 ∼20 000 au disc silhouette in M 17. We combined high-resolution JHKsL′ M′-band imaging carried out with Nasmyth Adaptive Optics System/Coudé Near Infrared Camera (NAOS/CONICA) at the Very Large Telescope (VLT) with [Fe ii] 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 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 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. © 2008 RAS.