The Cluster-forming Site AFGL 5157: Colliding Filamentary Clouds and Star Formation

We observationally investigate star formation process occurring in AFGL 5157 (area similar to 13.5 pc x 13.5 pc) using a multi-wavelength approach. Embedded filaments are seen in the Herschel column density map, and one of them is identified as an elongated filamentary feature (FF) (length similar to 8.3 pc; mass similar to 1170 M-circle dot). Five Herschel clumps (Mclump similar to 45-300 M-circle dot) are traced in the central part of the FF, where an extended temperature structure (T-d similar to 13.5-26.5 K) is observed. In the direction of the central part of the FF, the warmer region at T-d similar to 20-26.5 K spatially coincides with a mid-infrared shell surrounding a previously known evolved infrared cluster. Diffuse Ha emission is traced inside the infrared shell, suggesting the presence of massive stars in the evolved cluster. Based on the surface density analysis of young stellar objects (YSOs), embedded clusters of YSOs are traced toward the central part of the FF, and are distributed around the infrared shell. Previously detected H2O masers, H-2 knots, massive protostar candidates, and an H II region are also seen toward the embedded clusters. Using the (CO)-C-12 and (CO)-C-13 line data, the central part of the FF is observed at the overlapping zones of two filamentary molecular clouds (length similar to 12.5 pc) around -20 and -17 km s(-1), which are also connected in velocity. Our observational results suggest that the formation of massive stars appears to be triggered by a collision of two filamentary molecular clouds, which might have also influenced the birth of YSOs in AFGL 5157.