Multi-wavelength study of triggered star formation around 25 H II regions

We investigate 25 H II regions that show bubble morphology in (CO)-C-13(1-O) and infrared data, to search for quantitative evidence of triggered star formation by processes described by the collect and collapse (CC) and radiatively driven implosion (RDI) models. These H II regions display the morphology of a complete or partial bubble at 8 mu m, and are all associated with the molecular clouds that surround them. We found that the electron temperature ranges from 5627 K to 6839 K in these H II regions, and the average electron temperature is 6083 K. The age of these H II regions is from 3.0 x 10(5) yr to 1.7 x 10(6) yr, and the mean age is 7.7 x 10(5) yr. Based on the morphology of the associated molecular clouds, we divide these H II regions into three groups, which may support CC and RDI models. We select 23 young IRAS sources which have an infrared luminosity of >10(3) L-circle dot in 19 H II regions. In addition, we identify some young stellar objects (including Class I sources), which are only concentrated in H II regions G29.007+0.076, G44.339-0.827 and G47.028+0.232. The polycyclic aromatic hydrocarbon emissions of the three H II regions all show a cometary globule. Comparing the age of each H II region with the characteristic timescales for star formation, we suggest that the three H II regions can trigger clustered star formation by an RDI process. In addition, we detect seven molecular outflows in the five H II regions for the first time. These outflow sources may be triggered by the corresponding H II regions.