The high-mass star-forming region IRAS 18182-1433

¹ Max-Planck-Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany e-mail: beuther@mpia-hd.mpg.de
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA e-mail: name@cfa.harvard.edu
³ Centro de Radioastronomía y Astrofísica, UNAM, Apdo. Postal 3-72 (Xangari), 58089 Morelia, Michoacán, México

Received: 20 January 2006
Accepted: 23 March 2006

Abstract

Aims.We present mm line and continuum observations at high spatial resolution characterizing the physical and chemical properties of the young massive star-forming region IRAS 18182-1433.

Methods.The region was observed with the Submillimeter Array in the 1.3 mm band. The data are complemented with short-spacing information from single-dish CO(2–1) observations. SiO(1–0) data from the VLA are added to the analysis.

Results.Multiple massive outflows emanate from the mm continuum peak. The CO(2–1) data reveal a quadrupolar outflow system consisting of two outflows inclined by ~90°. One outflow exhibits a cone-like red-shifted morphology with a jet-like blue-shifted counterpart where a blue counter-cone can only be tentatively identified. The SiO(1–0) data suggest the presence of a third outflow. Analyzing the ¹²CO/¹³CO line ratios indicates decreasing CO line opacities with increasing velocities. Although we observe a multiple outflow system, the mm continuum peak remains single-peaked at the given spatial resolution (~13 500 AU). The other seven detected molecular species – also high-density tracers like CH₃CN, CH₃OH, HCOOCH₃ – are all ~1- offset from the mm continuum peak, but spatially associated with a strong molecular outflow peak and a cm emission feature indicative of a thermal jet. This spatial displacement between the molecular lines and the mm continuum emission could be either due to an unresolved sub-source at the position of the cm feature, or the outflow/jet itself alters the chemistry of the core enhancing the molecular abundances toward that region. A temperature estimate based on the CH₃CN lines suggests temperatures of the order of 150 K. A velocity analysis of the high-density tracing molecules reveals that at the given spatial resolution none of them shows any coherent velocity structure which would be consistent with a rotating disk. We discuss this lack of rotation signatures and attribute it to intrinsic difficulties to observationally isolate massive accretion disks from the surrounding dense gas envelopes and the molecular outflows.