The 10^5Lsun High-Mass Protostellar Object IRAS23151+5912

TL;DR

This study investigates the complex structure and outflows of the high-mass protostellar object IRAS23151+5912, revealing multiple condensations, molecular outflows, and a possible rotating toroid, advancing understanding of massive star formation stages.

Contribution

It provides high-resolution observations of IRAS23151+5912, identifying multiple condensations, outflows, and a rotating toroid, offering new insights into the transition phase of massive star formation.

Findings

Resolved submm continuum into at least two condensations.

Detected two molecular outflows via SiO(8-7) line maps.

Identified a large-scale rotating toroid without Keplerian rotation.

Abstract

While most sources above 10^5Lsun have already formed an Ultracompact HII region (UCHII), this is not necessarily the case for sources of lower luminosity. Characterizing sources in the transition phase, i.e., very luminous objects without any detectable free-free emission, is important for a general understanding of massive star formation. Therefore, we observed the luminous High-Mass Protostellar Object IRAS23151+5912 with the Submillimeter Array at 875mum in the submm continuum and spectral line emission at sub-arcsecond resolution. The 875mum submm continuum emission has been resolved into at least two condensations. The previously believed driving source of one of the outflows, the infrared source IRS1, is ~0.9'' offset from the main submm peak. Over the entire 4GHz bandwidth we detect an intermediate dense spectral line forest with 27 lines from 8 different species, isotopologues or vibrationally-torsionally excited states. Temperature estimates based on the CH3OH line series result in values of T(Peak1)~150+-50K and T(Peak2)~80~30K for the two submm peak positions, respectively. The SiO(8-7) red- and blue-shifted line maps indicate the presence of two molecular outflows. In contrast, the vibrationally-torsionally excited CH3OH line exhibits a velocity gradient approximately perpendicular to one of the outflows. With a size of approximately 5000AU and no Keplerian rotation signature, this structure does not resemble a genuine accretion disk but rather a larger-scale rotating toroid that may harbor a more common accretion disk at its so far unresolved center.