An irradiated jet in M 17⋆
ESO, Karl-Schwarzschild-Strasse 2,
Garching bei München,
2 Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
3 European Space Astronomy Centre (ESA), PO Box, 78, 28691 Villanueva de la Cañada, Madrid, Spain
Received: 23 July 2012
Accepted: 23 January 2013
Context. M 17 is one of the best studied giant HII regions in our galactic neighborhood. It should also provide a suitable environment for the class of fully ionized jets externally irradiated by the presence of nearby hot stars. However, no such jets have been observed thus far in M 17.
Aims. We report on a visible imaging survey of the M 17 nebula with the goal of identifying likely shock-excited nebulosities.
Methods. We imaged M 17 through narrow-band filters centered on the most intense visible lines of [OIII], Hα+[NII], [SII], and Hβ. We obtained follow-up spectroscopy of the only jet-like structure identified in the images. We also used published X-ray observations of M 17 obtained with the Chandra X-ray Observatory, as well as infrared data obtained with the Very Large Telescope and with the Spitzer Space Telescope, to look for evidence of a jet-driving source.
Results. We have detected what appears to be the first jet identified in M 17 visible HII region. The jet is composed of a set of knots, two of which have significant radial velocities with respect to the HII region, and a distant arc-like bright nebulosity that may represent an early episode of intense mass loss by the jet-driving source. The follow-up spectra of the structures composing the jet, including the arc, support this interpretation by revealing intense forbidden lines of [NII] and [SII] due to enhanced collisional excitation in shocks. The presence of a X-ray source, most likely a young stellar object, at a position where the jet launching source should be expected to lie reinforces the interpretation. We identify a tentative near-infrared counterpart of the X-ray source, although it is offset by 1".9 from the nominal position of the X-ray source, which is almost three times the radius of its positional uncertainty. The very weak [OI] emission in the spectra of the jet knots and the arc suggests that they are nearly fully ionized, in agreement with the environment in which the jet is propagating.
Key words: Herbig-Haro objects / HII regions / ISM: individual objects: M 17 / ISM: jets and outflows
Based on observations obtained with the IAC80 telescope operated on the island of Tenerife by the Instituto de Astrofísica de Canarias in the Spanish Observatorio del Teide, and with the ESO New Technology Telescope (NTT) at the Observatory of La Silla (Chile) under observing program 089.C-0189. This work also uses data downloaded from the ESO Science Archive Facility, originally obtained under observing run 69.C-0303(A).
© ESO, 2013