2012A&A...544A..39J

To increase the observational samples of star formation around expanding HII regions, we analyzed the interstellar medium and star formation around N22. We used data extracted from the seven large-scale surveys from infrared to radio wavelengths. In addition we used the JCMT observations of the J=3-2 line of emission data released on CADC and the J=2-1 and J=3-2 lines observed by the KOSMA 3m telescope. We performed a multiwavelength study of bubble N22. A molecular shell composed of several clumps agrees very well with the border of N22, suggesting that its expansion is collecting the surrounding material. The high integrated line intensity ratio R_ICO(3-2)_/ICO(2-1) (ranging from 0.7 to 1.14) implies that shocks have driven into the molecular clouds. We identify eleven possible O-type stars inside the HII region, five of which are located in projection inside the cavity of the 20cm radio continuum emission and are probably the exciting-star candidates of N22. Twenty-nine young stellar objects (YSOs) are distributed close to the dense cores of N22. We conclude that star formation is indeed active around N22; the formation of most of YSOs may have been triggered by the expanding of the HII region. After comparing the dynamical age of N22 and the fragmentation time of the molecular shell, we suggest that radiation-driven compression of pre-existing dense clumps may be ongoing.