New detection of near-infrared H₂ line emission in AFGL 5157

¹ Purple Mountain Observatory, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210008, PR China e-mail: yf.chen@pmo.ac.cn;yqyao@pmo.ac.cn;jiyang@pmo.ac.cn;qinzeng@pmo.ac.cn
² Department of Astrophysics, Nagoya University, Nagoya 464-0062, Japan e-mail: sato@z.phys.nagoya-u.ac.jp

Corresponding author: Yafeng Chen, yf.chen@pmo.ac.cn

Received: 23 August 2002
Accepted: 14 April 2003

Abstract

Narrow-band –0 S (1) and broad-band imaging observations towards AFGL 5157 revealed a number of new knots associated with the NH₃ core in the region, implying that the multiple H₂ outflows are driven by a cluster of embedded point sources in the core. The shell around the infrared cluster is more clearly seen than before, showing a few of newly detected ridge-like features. A string of knots newly revealed along one lobe of the known CO outflow suggests a parsec-scaled jet emanating from a young source in the core. These outflows and jet, together with the known compact H II region, radio continuum source, and H₂O masers further imply an extremely embedded cluster containing massive stars within it. The evidence shows that the massive young stars within the cluster are in a strong outflow stage of evolution, and together with the nearby infrared cluster in NGC 1985, further confirms that star forming process propagates from the west to the east in AFGL 5157. The two types of H₂ line emission, knots and shell, may be indicators of two different stages of star formation in clusters: the shocked H₂ knots are driven by the young stellar sources embraced in the younger cluster, while the diffuse shell-like structure comes from UV photons of relatively evolved cluster. The near-infrared nebula in AFGL 5157 is found to be only associated with the evolved cluster but not observed in the embedded cluster.