The infrared dust bubble N22: an expanding HII region and the star formation around it

TL;DR

This study investigates the interstellar medium and star formation activity around the infrared dust bubble N22, revealing that its expansion influences surrounding molecular clouds and likely triggers new star formation, including young stellar objects and candidate O-type stars.

Contribution

The paper provides a comprehensive multiwavelength analysis of N22, demonstrating the role of its expansion in collecting material and triggering star formation, with new candidate exciting stars identified.

Findings

Molecular shell aligns with N22's border, indicating expansion-driven material collection.

High CO line ratios suggest shocks in molecular clouds.

Active star formation, including YSOs and candidate O stars, is associated with N22.

Abstract

Aims. To increase the observational samples of star formation around expanding Hii regions, we analyzed the interstellar medium and star formation around N22. Methods. 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 12CO emission data released on CADC and the 12CO J = 2-1 and J =3-2 lines observed by the KOSMA 3 m telescope. We performed a multiwavelength study of bubble N22. Results. 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 12CO line intensity ratio (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 20 cm radio continuum emission and are probably the exciting-star candidates of N22. Twenty-nine YSOs (young stellar objects) 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.