Molecular jets driven by high-mass protostars: a detailed study of the IRAS 20126+4104 jet^*

¹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany e-mail: [caratti;jochen]@tls-tautenburg.de
² Centre for Astrophysics and Planetary Science, University of Kent, Canterbury, CT2 7NH, UK e-mail: df@star.kent.ac.uk
³ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio, Italy e-mail: [giannini;nisini]@oa-roma.inaf.it

Received: 5 February 2008
Accepted: 13 March 2008

Abstract

Context. 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 IRAS 20126+4104 molecular jet, driven by a 10 protostar, represents a suitable target to investigate.

Aims. We present here an extensive analysis of this protostellar jet, deriving the kinematical, dynamical, and physical conditions of the H₂ gas along the flow.

Methods. The jet was investigated by means of near-IR H₂ and [] narrow-band imaging, high-resolution spectroscopy of the 1–0 S(1) line (2.12 μm), NIR (0.9–2.5 μm) low-resolution spectroscopy, along with ISO-SWS and LWS spectra (from 2.4 to 200 μm).

Results. 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 –14 km s^-1 in the blue lobe, and from –8 to 47 km s^-1 in the red lobe. The low-resolution spectra are rich in H₂ emission, and relatively faint [] (NIR), [] and [] (FIR) emission is observed in the region close to the source. A warm H₂ gas component has an average excitation temperature that ranges between 2000 K and 2500 K. Additionally, the ISO-SWS spectrum reveals a cold component (520 K) that strongly contributes to the radiative cooling of the flow and plays a major role in the dynamics of the flow. The estimated of the jet is , suggesting that IRAS 20126+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 ((H yr^-1). 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.

Conclusions. As for a few other intermediate- and high-mass protostellar jets in the literature, we conclude that IRAS 20126+4104 jet is a scaled-up version of low-mass protostellar counterparts.