2008A&A...485..137C

Protostellar jets from intermediate- and high-mass protostars provide an excellent opportunity to understand the mechanisms responsible for intermediate- and high-mass star-formation. A crucial question is if they are scaled-up versions of their low-mass counterparts. Such high-mass jets are relatively rare and, usually, they are distant and highly embedded in their parental clouds. The IRAS20126+4104 molecular jet, driven by a 10⁴L_☉ protostar, represents a suitable target to investigate. We present here an extensive analysis of this protostellar jet, deriving the kinematical, dynamical, and physical conditions of the H₂ gas along the flow. The jet was investigated by means of near-IR H₂ and [FeII] narrow-band imaging, high-resolution spectroscopy of the 1-0S(1) line (2.12µm), NIR (0.9-2.5µm) low-resolution spectroscopy, along with ISO-SWS and LWS spectra (from 2.4 to 200µm). The flow shows a complex morphology. In addition to the large-scale jet precession presented in previous studies, we detect a small-scale wiggling close to the source, which may indicate the presence of a multiple system. The peak radial velocities of the H₂ knots range from -42 to -14km/s in the blue lobe, and from -8 to 47km/s in the red lobe. The low-resolution spectra are rich in H₂ emission, and relatively faint [FeII] (NIR), [OI] and [CII] (FIR) emission is observed in the region close to the source. A warm H₂ gas component has an average excitation temperature that ranges between 2000K and 2500K. Additionally, the ISO-SWS spectrum reveals a cold component (520K) that strongly contributes to the radiative cooling of the flow and plays a major role in the dynamics of the flow. The estimated L_H2 of the jet is 8.2±0.7L_☉, suggesting that IRAS20126+4104 has a significantly increased accretion rate compared to low-mass YSOs. This is also supported by the derived mass flux rate from the H₂ lines ({dot}(M)_out(H₂)∼7.5x10^–4M_☉/yr). The comparison between the H₂ and the outflow parameters strongly indicates that the jet is driving the outflow, at least partially. As already found for low-mass protostellar jets, the measured H₂ outflow luminosity is tightly related to the source bolometric luminosity. As for a few other intermediate- and high-mass protostellar jets in the literature, we conclude that IRAS20126+4104 jet is a scaled-up version of low-mass protostellar counterparts.