Microstructure and kinematics of H2O masers in the massive star forming region IRAS 06061+2151

TL;DR

This study used multi-epoch VLBI observations to analyze H2O masers in IRAS 06061+2151, revealing a bipolar outflow structure with a large opening angle and dual jet and molecular flow components, providing insights into massive star formation.

Contribution

First detailed kinematic model of H2O masers in IRAS 06061+2151 showing a biconical outflow with a large opening angle and dual structures in a massive star forming region.

Findings

Maser features are within 1 arcsecond of the UC HII region.

Maser kinematics are explained by a biconical outflow with >50° opening angle.

Detected a large velocity gradient indicating clumpy parental cloud structure.

Abstract

We have made multi-epoch VLBI observations of H2O maser emission in the massive star forming region IRAS 06061+2151 with the Japanese VLBI network (JVN) from 2005 May to 2007 October. The detected maser features are distributed within an 1\arcsec$\times$1\arcsec (2000 au$\times$2000 au at the source position) around the ultra-compact H {\small\bf II} region seen in radio continuum emission. Their bipolar morphology and expanding motion traced through their relative proper motions indicate that they are excited by an energetic bipolar outflow. Our three-dimensional model fitting has shown that the maser kinematical structure in IRAS 06061+2151 is able to be explained by a biconical outflow with a large opening angle ($>$ 50\degr). The position angle of the flow major axis coincides very well with that of the large scale jet seen in 2.1$\:\mu\rmn{m}$ hydrogen emission. This maser geometry indicates the existence of dual structures composed of a collimated jet and a less collimated massive molecular flow. We have also detected a large velocity gradient in the southern maser group. This can be explained by a very small (on a scale of several tens of au) and clumpy (the density contrast by an order of magnitude or more) structure of the parental cloud. Such a structure may be formed by strong instability of shock front or splitting of high density core.