Observational signatures of cloud-cloud collision in the extended star-forming region S235

TL;DR

This study provides multi-wavelength evidence of cloud-cloud collision in the star-forming region S235, linking it to triggered star formation and the emergence of young stellar objects at cloud interfaces.

Contribution

It offers observational support for cloud-cloud collision triggering star formation in S235, aligning with numerical models and identifying specific regions influenced by this process.

Findings

Identification of two molecular clouds with distinct velocities separated by ~4 km/s.

Detection of a broad bridge feature indicating interaction between the clouds.

Young stellar populations and compact H II regions are concentrated at the cloud interface.

Abstract

We present a multi-wavelength data analysis of the extended star-forming region S235 (hereafter E-S235), where two molecular clouds are present. In E-S235, using the 12CO (1-0) and 13CO (1-0) line data, a molecular cloud linked with the site "S235main" is traced in a velocity range [-24, -18] km s^{-1}, while the other one containing the sites S235A, S235B, and S235C (hereafter "S235ABC") is depicted in a velocity range [-18, -13] km s^{-1}. In the velocity space, these two clouds are separated by ~4 km s^{-1}, and are interconnected by a lower intensity intermediate velocity emission, tracing a broad bridge feature. In the velocity channel maps, a possible complementary molecular pair at [-21, -20] km s^{-1} and [-16, -15] km s^{-1} is also evident. The sites, "S235ABC", East 1, and South-West are spatially seen in the interface of two clouds. Together, these observed features are consistent with the predictions of numerical models of the cloud-cloud collision (CCC) process, favoring the onset of the CCC in E-S235 about 0.5 Myr ago. Deep UKIDSS near-infrared photometric analysis of point-like sources reveals significant clustering of young stellar populations toward the sites located at the junction, and the "S235main". The sites, "S235ABC" harbor young compact H II regions having dynamical ages of ~0.06-0.22 Myr, and these sites (including South-West and East 1) also contain dust clumps (having M_clump ~40 to 635 M_sun). Our observational findings suggest that the star formation activities (including massive stars) appear to be influenced by the CCC mechanism at the junction.