Submillimeter observations of the isolated massive dense clump IRAS 20126+4104

Abstract

We imaged the 350 and 450 μm continuum and CO J = 6–5 line emission of the IRAS 20126+4104 clump at the CSO. The continuum and line observations show that the clump has a radius of ~0.5 pc. The clump has a radial density profile α r^(−1.2) for r ≾ 0.1 pc and has α r^(−2.3) for r ≳ 0.1 pc, which suggests that the inner region is infalling, while the infall wave has not yet reached the outer region. Based on the 350 μm/450 μm flux ratio map, three distinct regions are identified: a bipolar feature that coincides with the large scale CO bipolar outflow; a cocoon-like region that encases the bipolar feature and has a warm surface; and a cold layer outside of the cocoon region. The complex flux ratio pattern indicates that the clump is no longer uniform in terms of temperature as well as dust properties. The CO emission near the systemic velocity traces the dense clump and the outer layer of the clump shows narrow line widths (≾3 km s^(−1)). The clump has a velocity gradient of ~2 km s^(−1) pc^(−1), which we interpret as due to rotation of the clump, as the equilibrium mass (~200 M⊙) is comparable to the LTE mass. Over a scale of ~1 pc, the clump rotates in the opposite sense with respect to the ≾0.03 pc disk associated with the (proto)star. This is one of four objects in high-mass and low-mass star-forming regions for which a discrepancy between the rotation sense of the envelope and the core has been found, suggesting that such a complex kinematics may not be unusual in star-forming regions.

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