2013A&A...551A..43J

While it is currently unclear from a theoretical standpoint which forces and processes dominate the formation of high-mass stars, and hence determine the mode in which they form, much of the recent observational evidence suggests that massive stars are born in a similar manner to their low-mass counterparts. This paper aims to investigate the hypothesis that the embedded luminous star AFGL2591-VLA3 (2.3x10⁵L_☉ at 3.33kpc) is forming according to a scaled-up version of a low-mass star formation scenario. We present multi-configuration Very Large Array (VLA) 3.6cm and 7mm, as well as Combined Array for Research in Millimeter Astronomy C¹⁸O and 3mm continuum observations to investigate the morphology and kinematics of the ionized gas, dust, and molecular gas around AFGL2591. We also compare our results to ancillary Gemini North near-IR images, and model the near-IR to sub-mm spectral energy distribution (SED) and Two Micron All Sky Survey (2MASS) image profiles of AFGL2591 using a Monte-Carlo dust continuum radiative transfer code. The observed 3.6 cm images uncover for the first time that the central powering source AFGL2591-VLA3 has a compact core plus collimated jet morphology, extending 4000AU eastward from the central source with an opening angle of <10° at this radius. However, at 7mm VLA3 does not show a jet morphology, but instead compact (<500AU) emission, some of which (<0.57mJy of 2.9mJy) is estimated to be from dust emission. The spectral index of AFGL2591-VLA3 between 3.6cm and 7mm was found to be between 0.4 and 0.5, similar to that of an ionized wind. If the 3.6cm emission is modelled as an ionized jet, the jet has almost enough momentum to drive the larger-scale flow. However, assuming a shock efficiency of 10%, the momentum rate of the jet is not sufficient to ionize itself via only shocks, and thus a significant portion of the emission is instead likely created in a photoionized wind. The C¹⁸O emission uncovers dense entrained material in the outflow(s) from these young stars. The main features of the SED and 2MASS images of AFGL2591-VLA3 are also reproduced by our model dust geometry of a rotationally flattened envelope with and without a disk. The above results are consistent with a picture of massive star formation similar to that seen for low-mass protostars. However, within its envelope, AFGL2591-VLA3 contains at least four other young stars, constituting a small cluster. Therefore it appears that AFGL2591-VLA3 may be able to source its accreting material from a shared gas reservoir while still exhibiting the phenomena expected during the formation of low-mass stars.