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Register a new userA Multi-wavelength Study of the Massive Star-forming Region S87
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Rui Xue Department of Astronomy
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This article presents a multi-wavelength study towards S87, based on a dataset of submillimeter/far-/mid-infrared (sub-mm/FIR/MIR) images and molecular line maps. The sub-mm continuum emission measured with JCMT/SCUBA reveals three individual clumps, namely, SMM1, SMM2, and SMM3. The MIR/FIR images obtained by the Spitzer Space Telescope indicate that both SMM1 and SMM3 harbor point sources. The J=1-0 transitions of CO, 13CO, C18O, and HCO+, measured with the 13.7m telescope of the Purple Mountain Observatory, exhibit asymmetric line profiles. Our analysis of spectral energy distributions (SEDs) shows that all of the three sub-mm clumps are massive (110--210 $M_{odot}$), with average dust temperatures in the range ~20--40K. A multi-wavelength comparison convinces us that the asymmetric profiles of molecular lines should result from two clouds at slightly different velocities, and it further confirms that the star-forming activity in SMM1 is stimulated by a cloud-cloud collision. The stellar contents and SEDs suggest that SMM1 and SMM3 are high-mass and intermediate-mass star-forming sites respectively. However, SMM2 has no counterpart downwards 70 micron, which is likely to be a cold high-mass starless core. These results, as mentioned above, expose multiple phases of star formation in S87.
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Context. With the latest infrared surveys, the number of massive protostellar candidates has increased significantly. New studies have posed additional questions on important issues about the formation, evolution, and other phenomena related to them. Complementary to infrared data, radio observations are a good tool to study the nature of these objects, and to diagnose the formation stage. Aims. Here we study the far-infrared source IRAS 16353-4636 with the aim of understanding its nature and origin. In particular, we search for young stellar objects (YSOs), possible outflow structure, and the presence of non-thermal emission. Methods. Using high-resolution, multi-wavelength radio continuum data obtained with the Australia Telescope Compact Array, we image IRAS 16353-4636 and its environment from 1.4 to 19.6 GHz, and derive the distribution of the spectral index at maximum angular resolution. We also present new JHKs photometry and spectroscopy data obtained at ESO NTT. 13 CO and archival HI line data, and infrared databases (MSX, GLIMPSE, MIPSGal) are also inspected. Results. The radio continuum emission associated with IRAS 16353-4636 was found to be extended (~10 arcsec), with a bow-shaped morphology above 4.8 GHz, and a strong peak persistent at all frequencies. The NIR photometry led us to identify ten near-IR sources and classify them according to their color. We used the HI line data to derive the source distance, and analyzed the kinematical information from the CO and NIR lines detected. Conclusions. We have identified the source IRAS 16353-4636 as a new protostellar cluster. In this cluster we recognized three distinct sources: a low-mass YSO, a high-mass YSOs, and a mildly confined region of intense and non-thermal radio emission. We propose the latter corresponds to the terminal part of an outflow.
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