Molecular gas in a system of two interacting galaxies overlapping on the line of sight

¹ LUX, Observatoire de Paris, Sorbonne Université, Université PSL, CNRS, F-75014 Paris, France
² Centre for Astrophysics and Supercomputing, Swinburne University of Technology, PO Box 218 Hawthorn, VIC 3122, Australia
³ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia
⁴ Steward Observatory, University of Arizona, 933 N Cherry Av, Tucson, AZ 85721, USA
⁵ Collège de France, 11 Place Marcelin Berthelot, F-75005 Paris, France

^★ Corresponding author: anaelle.halle@observatoiredeparis.psl.eu

Received: 24 July 2025
Accepted: 6 October 2025

Abstract

Galaxy interactions can disturb gas in galactic discs, compress it, excite it, and enhance star formation. An intriguing system likely consisting of two interacting galaxies overlapping on the line of sight was previously studied through ionised gas observations from the integral-field spectrograph Mapping Nearby Galaxies at APO (MaNGA). A decomposition into two components using MaNGA spectra, together with a multi-wavelength study, allowed us to characterise the system as a minor-merger with interaction-induced star-formation, and perhaps active galactic nucleus (AGN) activity. We used new interferometric observations of the CO(1–0) gas of this system from the NOrthern Extended Millimeter Array (NOEMA) to confront and combine the spatially resolved ionised and molecular gas observations. Mock NOEMA and MaNGA data are computed from simulated systems of two discs and compared to the observations. The NOEMA observations of the molecular gas, dynamically colder than the ionised gas, help to constrain the configuration of the system, which we revisited as a major merger. A combination of ionised and molecular gas data allowed us to study the star-formation efficiency of the system.