Colliding filaments in the molecular cloud G34

¹ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi 830011, PR China
² University of the Chinese Academy of Sciences, Beijing 100080, PR China
³ State Key Laboratory of Radio Astronomy and Technology, A20 Datun Road, Chaoyang District, Beijing 100101, PR China
⁴ Xinjiang Key Laboratory of Radio Astrophysics, Urumqi 830011, PR China
⁵ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁶ Energetic Cosmos Laboratory, Nazarbayev University, Astana 010000, Kazakhstan
⁷ Institute of Experimental and Theoretical Physics, Al-Farabi Kazakh National University, Almaty 050040, Kazakhstan
⁸ Netherlands Institute for Radio Astronomy, ASTRON, 7991 PD Dwingeloo, The Netherlands
⁹ Ural Federal University, 19 Mira Street, 620002 Ekaterinburg, Russia
¹⁰ Department of Electronics and Astrophysics, Faculty of Physics and Technology, Al-Farabi Kazakh National University, Almaty 050040, Kazakhstan

^★ Corresponding authors: sunmingke@xao.ac.cn; jarken@xao.ac.cn; chenkel@mpifr-bonn.mpg.de

Received: 22 January 2025
Accepted: 22 July 2025

Abstract

The molecular cloud complex G34 is located at a distance of 2.12 ± 0.38 kpc and contains two giant filaments, F1 and F2. It is considered a good example of colliding filaments. We mapped these two filaments using the ¹³CO and ¹²CO (J = 1−0) lines that were observed with the 13.7 m millimeter-wavelength telescope of the Purple Mountain Observatory. The fraction of high-column density gas N_H2 > 1.0 × 10²² cm⁻² in F1 and F2 is 4.16% and 8.33%, respectively, which is lower than the typical value of 10% for giant molecular filaments. Moreover, only one of the 13 dense clumps identified in F1 and F2 correlates with the infrared dust cores traced by the NASA Wide-field Infrared Survey Explorer (WISE) 22 μm emission. This suggests that F1 and F2 may be in early stages of their evolution and might be forming low-mass stars. We also observe large-scale velocity gradients in F1 and F2. Along the spine of F1, the velocity and line mass increase from the ends toward the center, while in F2, they increase from the northwest to the southeast. These parameters are inversely correlated with the gravitational potential, which may indicate a transformation between kinetic energy and gravitational potential energy between F1 and F2. Furthermore, no H II regions correlate with F1 and F2 in the WISE data of galactic H II regions, which indicates that the gas distribution within F1, as well as the V-shaped structure of F1, is unaffected by feedback from H II regions, but is instead caused by gravitational effects. The material in F1 and F2 is not concentrated at the ends of the filaments, but rather in the middle of F1 and at one end of F2 and therefore does not lead to the edge-collapse effect. The collapse and merging timescales thus do not compete. Finally, we calculated the merging time of F1 and F2. When the angle between the line-of-sight velocity and the direction of the relative velocity between F1 and F2 is 45°, the average relative velocity between F1 and F2 is 1.39 km s⁻¹. The resulting merging timescale is approximately 4.62 ± 1.12 Myr. This process might be influenced by additional stellar feedback from ongoing star formation within the filaments.