A New Cloud-Cloud Collision Source N68 toward the G35 Molecular Cloud Complex

TL;DR

This study identifies cloud-cloud collision signatures in Bubble N68 within the G35 complex, linking it to active star formation and massive star triggering, and situates it within a larger 100 pc scale collision system.

Contribution

It provides the first detailed molecular evidence of cloud-cloud collision in Bubble N68 and its role in massive star formation within the G35 complex.

Findings

Two molecular clouds show broad bridge features indicating ongoing collision.

Star formation is driven by multiple mechanisms, with CCC mainly triggering massive stars.

N68 is part of a larger 100 pc scale cloud-cloud collision system.

Abstract

Bubble N68 in the G35 complex shows clear cloud-cloud collision (CCC) signatures. Its semi-ring-like morphology harbors many significant massive star formation tracers: 6 HII regions, 4 6.7 GHz masers, 5 Midcourse Space Experiment sources, 9 radio peaks, and nearly 10 O/B-type stars. We also identified 163 young stellar objects (45 Class I, 5 Flat, 113 Class II), indicating active star formation toward N68. Our molecular study with CO reveals two distinct molecular clouds (N68a: 47-56 km s$^{-1}$; N68b: 56-64 km s$^{-1}$), with broad bridge features and complementary distributions at their borders, indicating an ongoing CCC. Star formation in N68 is collectively driven by collect-and-collapse (CC), radiation-driven implosion (RDI), and CCC mechanisms. However, compared with the CC and RDI mechanisms, the CCC mechanism does not enhance the star formation efficiency; instead, it tends to trigger the formation of massive stars. N68, along with bubbles N65 and N61, constructs a $\sim100$ pc scale CCC system in the G35 complex.