Cloud-cloud collision in S235: triggered the formation of high-mass stars and young star clusters

Abstract

We present the analysis of cloud-cloud collision (CCC) process in the Galactic molecular complex S235. Our new CO observations performed with the PMO-13.7 m telescope reveal two molecular clouds, namely the S235-Main and the S235-ABC, with ~4 km s^-1 velocity separation. The bridge feature, the possible colliding interface and the complementary distribution of the two clouds are significant observational signatures of cloud-cloud collision in S235. The most direct evidence of cloud-cloud collision process in S235 is that the S235-Main (in a distance of 1547$^{+44}_{-43}$ pc) and S235-ABC (1567$^{+33}_{-39}$ pc) meet at almost the same position (within 1σ error range) at a supersonic relative speed. We identified ten ¹³CO clumps from PMO-13.7 m observations, 22 dust cores from the archival SCUBA-2 data, and 550 YSOs from NIR-MIR data. 63 per cent of total YSOs are clustering in seven MST groups (M1-M7). The tight association between the YSO groups (M1 $\&$ M7) and the bridge feature suggests that the CCC process triggers star formation there. The collisional impact subregion (the South) shows 3 ~ 5 times higher CFE and SFE (average value of 12.3 and 10.6 per cent, respectively) than the non-collisional impact subregion (2.4 and 2.6 per cent, respectively), suggesting that the CCC process may have enhanced the CFE and SFE of the clouds compared to those without collision influence.