The study of a system of H II regions toward l = 24.8 deg, b = 0.1 deg at the Galactic bar - Norma arm interface

TL;DR

This study investigates a complex of H II regions near the Galactic bar and Norma arm, revealing cloud interactions and star formation triggered by molecular cloud collisions at this dynamic galactic interface.

Contribution

It provides a detailed multi-wavelength analysis of H II regions at the bar-arm interface, highlighting cloud interactions and triggered star formation mechanisms.

Findings

Presence of interacting molecular clouds at the interface.

Detection of active star formation and O-type stars.

Evidence of cloud collision triggering star formation.

Abstract

To probe the star formation (SF) process, we present a thorough multi-wavelength investigation of several H II regions located toward l = 24.8 deg, b = 0.1 deg. A system of at least five H II regions including the mid-infrared bubble N36 (hereafter "system N36"; extension ~35 pc) is observationally investigated, and is located at a distance of 6.0 kpc. With this distance, the system N36 is found to be situated at the interface of the Galactic bar and the Norma Galactic arm in our Galaxy, where one may expect the collisions of molecular clouds due to the bar potential. Each H II region (dynamical age ~0.4 - 1.3 Myr) in the system is powered by an O-type star. The system contains 27 ATLASGAL dust clumps at 870 micron. Several clumps are massive (> 10^3 M_sun), and have high bolometric luminosity (> 10^3 L_sun). Using the GRS 13CO line data, in the direction of the system N36, two velocity components are found around 109 and 113 km/s, and are linked in the velocity space. The morphological analysis of 13CO favours the presence of interacting molecular clouds in the system. Four H II regions and two 6.7 GHz masers are spatially observed at the common areas of the two clouds. The analysis of the Spitzer photometric data also traces the noticeable SF activity in the system. Considering the observational outcomes, the formation of O-type stars (including ongoing SF) in the system appears to be triggered by the collisions of molecular clouds at the bar-arm interface.