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arXiv · 2610.03346

A multi-scale view of molecular gas and magnetic fields in the Antennae galaxies

Akhil Lasrado·Enrique Lopez-Rodriguez·Claudia Cicone·Axel Weiss·Andreas Lundgren·Boy Lankhaar·Robert Wissing·Sijing Shen
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Abstract

Major mergers are transformative events in galaxy evolution, dynamically reshaping the stellar and gas makeup of the hosts, as well as the galaxy-scale magnetic fields (B-fields) that permeate their interstellar medium (ISM), altering both B-field strength and configuration. In this work, we study in detail the link between the co-evolving gas and B-fields in the cold ISM phase of the nearby Antennae galaxy merger (NGC 4038/4039), using CO(3-2) data from the LAsMA receiver at the APEX telescope and ALMA, together with archival 154 $μ$m dust polarization data from the SOFIA/HAWC+. We characterize trends between measurements of molecular gas intensity and velocity dispersion with polarization measurements at kpc-scales with the APEX and SOFIA data. We find anti-correlations with CO intensity ($ρ\lesssim-0.6$) and CO velocity dispersion ($ρ\lesssim-0.4$), which are signposts of geometric depolarization. Since dust polarization measurements are a density-weighted line-of-sight integrated average of B-field vectors below the beam size, the ALMA data can serve as a proxy of density structures below the SOFIA beam on a channel-by-channel basis. Through a geometric analysis of structures in the ALMA channels, we identify salient kinematic features in the overlap region strongly aligned with the SOFIA-inferred B-field orientation. This indicates that these kinematic features might dominantly lend their orientation to the measured field direction, assuming a correspondence between molecular gas structures and galactic B-fields, owing to their density or high polarization fraction. We also identify a modest trend ($ρ\sim0.5$) between the coherence of the molecular gas, a proxy of the line-of-sight angular dispersion, at small scales, and the SOFIA polarization fraction, showing that the polarization fraction measured at $\sim2$ kpc scales is sensitive to structures at $\sim50$ pc scales.

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Akhil Lasrado, Enrique Lopez-Rodriguez, Claudia Cicone, Axel Weiss, Andreas Lundgren, Boy Lankhaar, Robert Wissing, Sijing Shen. 2026-10-02. A multi-scale view of molecular gas and magnetic fields in the Antennae galaxies. https://arxiv.org/abs/2610.03346

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