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

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 consis ting of two outflows inclined by ∼90 ◦ . One outflow exhibits a cone-like red-shifted morphology wi th 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 12 CO/ 13 CO line ratios indicates decreasing CO line opacities with increasing velocities. Although we observe a multiple outflow system, the m m continuum peak remains single-peaked at the given spatial resolution (∼13500 AU). The other seven detected molecular species ‐ also high-density tracers like CH3CN, CH3OH, HCOOCH3 ‐ are all∼1-2 ′′ 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(12k− 11k) lines suggests temperatures of the order 150 K. A velocity analysis of the high-density tracing molecules reveals that at the given spatial resolutio n none of them shows any coherent velocity structure which would be consistent with a rotating disk. We discuss this lack of rotation signatu res and attribute it to intrinsic diffi culties to observationally isolate massive accretion disk s from the surrounding dense gas envelopes and the molecular outflows.