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

TL;DR

This study combines ionised and molecular gas observations from MaNGA and NOEMA to analyze a galaxy system, revealing it as a major merger with enhanced star formation and providing detailed insights into gas dynamics.

Contribution

It is the first to integrate spatially-resolved ionised and molecular gas data for this system, revising its classification from minor to major merger.

Findings

Molecular gas is dynamically colder than ionised gas.

The system is a major merger, not a minor one.

Star-formation efficiency is studied through combined gas data.

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 to characterise the system as a minor-merger with interaction-induced star-formation, and maybe AGN activity. We use 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 precise the configuration of the system, which we revisit as being a major merger. Combination of ionised and molecular gas data allow us to study the star-formation efficiency of the system.