Multi-wavelength study of triggered star formation around mid-infrared   bubble N14
  We present multi-wavelength analysis around mid-infrared bubble N14 to probe the signature of triggered star formation as well as the formation of new massive star(s) and/or cluster(s) on the borders of the bubble by the expansion of the H II region. Spitzer-IRAC ratio maps reveal that the bubble is traced by the polycyclic aromatic hydrocarbon emission following an almost circular morphology except in the south-west direction towards the low molecular density environment. The observational signatures of the collected molecular and cold dust material have been found around the bubble. We have detected 418 YSOs in the selected region around the bubble N14. Interestingly, the detected YSO clusters are associated with the collected molecular and cold dust material on the borders of the bubble. One of the clusters is found with deeply embedded intermediate mass and massive Class I YSOs associated with one of the dense dust clumps in the east of the bubble N14. We do not find a good agreement between the dynamical age of the H II region and the fragmentation time of the accumulated molecular materials to explain possible "collect-and-collapse" process around the bubble N14. Therefore, we suggest the possibility of triggered star formation by compression of the pre-existing dense clumps by the shock wave and/or small scale Jeans gravitational instabilities in the collected materials. We have also investigated 5 young massive embedded protostars (8 to 10 M_sun) and 15 intermediate mass (3 to 7 M_sun) Class I YSOs which are associated with the dust and molecular fragmented clumps at the borders of the bubble. We conclude that the expansion of the H II region is also leading to the formation of these intermediate and massive Class I YSOs around the bubble N14. 
L. K. Dewangan and D. K. Ojha
astro-ph.GA