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

• Published in: Monthly notices of the Royal Astronomical Society 2008-10, Vol.390 (2), p.523-534
• Main Authors: Motogi, K., Watanabe, Y., Sorai, K., Habe, A., Honma, M., Imai, H., Yamauchi, A., Kobayashi, H., Fujisawa, K., Omodaka, T., Takaba, H., Shibata, K. M., Minamidani, T., Wakamatsu, K., Sudou, H., Kawai, E., Koyama, Y.
• Format: Article
• Language: English
• Subjects: Astronomy; Astrophysics; Earth, ocean, space; Exact sciences and technology; ISM: jets and outflows; ISM: kinematics and dynamics; Kinematics; masers; Star & galaxy formation; stars: formation
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2008.13727.x

We have made multi-epoch very long baseline interferometer (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 a 1 × 1 arcsec2 area (2000 × 2000 au2 at the source position) around the ultracompact H ii region seen in radio continuum emission. The 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 can be explained by a biconical outflow with a large opening angle (>50°). The position angle of the flow major axis coincides very well with that of the large-scale jet seen in 2.1 μm 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 astronomical units) 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 the shock front or splitting of the high density core.