Formation of a massive protostar through disk accretion^*

II. SINFONI integral field spectroscopy of the M 17 silhouette disk and discovery of the associated H₂ jet

¹ European Southern Observatory, Casilla 19001, Santiago 19, Chile e-mail: dnuernbe@eso.org
² Astronomisches Institut der Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum, Germany
³ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
⁴ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany

Received: 19 May 2006
Accepted: 12 December 2006

Abstract

Context.Recent observational results suggest that high-mass (proto-)stars form in a similar way to low- and intermediate-mass stars, i.e., via disk accretion of gas and dust.

Aims.To further characterize and understand the on-going physical processes associated with a large circumstellar disk, seen as a dark silhouette against the bright background of the M 17 H ii region, we report and discuss new high angular resolution integral field spectroscopy performed in the K-band.

Methods.The data were taken with the Adaptive Optics (AO) supported near-infrared integral field spectrograph SINFONI at ESO's Very Large Telescope Yepun (VLT UT 4) as part of the science verification of this new instrument.

Results.Based on obtained H₂ –0 S(1) and H₂ –0 S(3) emission maps, we report the discovery of a H₂ jet, which apparently arises from the suspected protostellar source(s) located at the very center of the disk. In addition, both diameter (about 4000 AU) and sub-structures of the innermost, densest part of the flared disk are infered from Br γ, Br δ, and He I maps.

Conclusions.Because ejection of material through a jet/outflow is always linked to accretion of gas and dust either onto the circumstellar disk or onto the central (protostellar) source(s), the presence of a collimated H₂ jet provides indirect but unquestionable evidence for ongoing accretion processes in the case of the M 17 disk. The high mass outflow and accretion rates of >10^-5  derived from the SINFONI data suggest that a star of rather high mass is forming.