Low-velocity large-scale shocks in the infrared dark cloud G035.39-00.33: Bubble-driven cloud-cloud collisions

¹ Institut de Radioastronomie Millimétrique, 300 Rue de la Piscine, 38400 Saint-Martin-d’Hères, France
² Centro de Astrobiología (CSIC/INTA), Ctra. de Torrejón a Ajalvir km 4, Madrid, Spain
³ National Astronomical Observatories of China, Chinese Academy of Sciences, Beijing 100012, China
⁴ INAF Osservatorio Astronomico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
⁵ Department of Space, Earth and Environment, Chalmers University of Technology, 412 96 Gothenburg, Sweden
⁶ Department of Astronomy, University of Virginia, 530 McCormick Road Charlottesville, 22904-4325 USA
⁷ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
⁸ European Southern Observatory (ESO), Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany
⁹ Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse 1, 85748 Garching bei München, Germany
¹⁰ Laboratory for the study of the Universe and eXtreme phenomena (LUX), Observatoire de Paris, 5, place Jules Janssen, 92195 Meudon, France
¹¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

^★ Corresponding author: giuliana.cosentino@iram.fr

Received: 23 June 2025
Accepted: 7 August 2025

Abstract

Context. Low-velocity, large-scale shocks impacting on the interstellar medium have been suggested as efficient mechanisms that shape molecular clouds and trigger star formation within them.

Aims. These shocks, both driven by galactic bubbles and/or cloud-cloud collisions, leave specific signatures in the morphology and kinematics of the gas. Observational studies of such signatures are crucial to investigate if and how shocks affect the clouds formation process and trigger their future star formation.

Methods. We have analysed the shocked and dense gas tracers SiO(2−1) and H¹³ CO⁺(1−0) emission towards the Infrared Dark Cloud G035.39-00.33, using new, larger-scale maps obtained with the 30 m telescope at the Instituto de Radioastronomía Millimétrica.

Results. We find that the dense gas is organised into a northern filament and a southern one that have different velocities and tilted orientations with respect to each other. The two filaments, seen in H¹³ CO⁺, are spatially separated yet connected by a faint bridge-like feature also seen in a position-velocity diagram extracted across the cloud. This bridge feature, typical of cloud-cloud collisions, also coincides with a very spectrally narrow SiO-traced gas emission. We suggest that the northern filament is interacting with the nearby supernova remnant G035.6-0.4. Towards the southern filament, we also report the presence of a parsec-scale, spectrally narrow SiO emission likely driven by the interaction between this filament and a nearby expanding shell. The shell is visible in the 1.3 GHz and 610 MHz continuum images and our preliminary analysis suggests it may be the relic of a supernova remnant.

Conclusions. We conclude that the two filaments represent the densest part of two colliding clouds, pushed towards each other by nearby supernova remnants. We speculate that this cloud-cloud collision driven by stellar feedback may have assembled the infrared dark cloud. We also evaluate the possibility that star formation may have been triggered within G035.39-00.33 by the cloud-cloud collision.