Cloud-cloud collision and star formation in G323.18+0.15

¹ XingJiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi 830011, PR China
e-mail: mayingxiu@xao.ac.cn; zhoujj@xao.ac.cn
² University of Chinese Academy of Sciences, Beijing 100049, PR China
³ Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Urumqi 830011, PR China
⁴ Xinjiang Key Laboratory of Radio Astrophysics, Urumqi 830011, PR China
⁵ Netherlands Institute for Radio Astronomy, ASTRON, 7991 PD Dwingeloo, The Netherlands
⁶ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁷ Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, PR China

Received: 11 February 2022
Accepted: 17 May 2022

Abstract

We studied the cloud-cloud collision candidate G323.18+0.15 based on signatures of induced filaments, clumps, and star formation. We used archival molecular spectrum line data from the SEDIGISM ¹³CO (J = 2−1) survey, from the Mopra southern Galactic plane CO survey, and infrared to radio data from the GLIMPSE, MIPS, Hi-GAL, and SGPS surveys. Our new result shows that the G323.18+0.15 complex is 3.55 kpc away from us and consists of three cloud components, G323.18a, G323.18b, and G323.18c. G323.18b shows a perfect U-shape structure, which can be fully complemented by G323.18a, suggesting a collision between G323.18a and the combined G323.18bc filamentary structure. One dense compressed layer (filament) is formed at the bottom of G323.18b, where we detect a greatly increased velocity dispersion. The bridge with an intermediate velocity in a position-velocity diagram appears between G323.18a and G323.18b, which corresponds to the compressed layer. G323.18a plus G323.18b as a whole are probably not gravitationally bound. This indicates that high-mass star formation in the compressed layer may have been caused by an accidental event. The column density in the compressed layer of about 1.36 × 10²² cm⁻² and most of the dense clumps and high-mass stars are located there. The average surface density of class I and class II young stellar objects (YSOs) inside the G323.18+0.15 complex is much higher than the density in the surroundings. The timescale of the collision between G323.18a and G323.18b is 1.59 Myr. This is longer than the typical lifetime of class I YSOs and is comparable to the lifetime of class II YSOs.