Interaction Between HII Region and AFGL333-Ridge: Implications to the Star Formation Scenario

TL;DR

This study investigates star formation in the AFGL333 region near the W4 bubble, revealing a mix of triggered and quiescent star formation influenced by the interaction of HII regions and molecular clouds.

Contribution

It provides detailed observational evidence of the interaction between HII regions and molecular clouds, highlighting the coexistence of triggered and quiescent star formation modes.

Findings

Large velocity widths indicate interaction between HII regions and molecular clouds.

Star formation in the core appears to be quiescent, not externally triggered.

Evidence of both triggered and quiescent star formation in the region.

Abstract

We investigated the star formation activities in the AFGL333 region, which is in the vicinity of the W4 expanding bubble, by conducting NH3 (1,1), (2,2), and (3,3) mapping observations with the 45 m Nobeyama Radio Telescope at an angular resolution of 75". The morphology of the NH3 (1,1) map shows a bow-shape structure with the size of 2.0 x 0.6 pc as seen in the dust continuum. At the interface between the W4 bubble and the dense NH3 cloud, the compact HII region G134.2+0.8, associated with IRAS02245+6115, is located. Interestingly, just north and south of G134.2+0.8 we found NH3 emission exhibiting large velocity widths of ~ 2.8 km/s, compared to 1.8 km/s at the other positions. As the possibility of mechanical energy injection through the activity of YSO(s) is low, we considered the origin of the large turbulent gas motion as indication of interaction between the compact HII region and the periphery of the dense molecular cloud. We also found expanding motion of the CO emission associated with G134.2+0.8. The overall structure of the AFGL333-Ridge might have been formed by the expanding bubble of W4. However, the small velocity widths observed west of IRAS02245+6115, around the center of the dense molecular cloud, suggest that interaction with the compact HII region is limited. Therefore the YSOs (dominantly Class 0/I) in the core of the AFGL333-Ridge dense molecular cloud most likely formed in quiescent mode. As has been previously suggested for the large scale star formation in the W3 giant molecular cloud, our results show an apparent coexistence of induced and quiescent star formation in this region. It appears that star formation in the AFGL333 region has proceeded without significant external triggers, but accompanying stellar feedback environment.