Multiple gas acquisition events in galaxies with dual misaligned gas disks

TL;DR

This study reports the discovery of galaxies with two misaligned gas disks, indicating multiple recent gas acquisition events, which challenges traditional models of galaxy formation and angular momentum accumulation.

Contribution

It presents the first observed cases of galaxies with two misaligned gas disks, revealing complex gas accretion histories not previously documented.

Findings

Both galaxies contain two gas disks misaligned with each other and the stellar disk.

Star formation is enhanced at the interface of the two gas disks.

The misalignments exceed 120° between the two gas disks.

Abstract

Frequent accretion of external cold gas is thought to play an important role in galaxy assembly. However, almost all known kinematically misaligned galaxies identify only one gas disk that is misaligned with the stellar disk, implying a single gas acquisition event. Here we report a new configuration in two galaxies where both contain two gas disks misaligned with each other and also with the stellar disk. Such systems are not expected to be stable or long-lasting, challenging the traditional picture of gas accretion of galaxies and their angular momentum build-up. The differences in kinematic position angles are larger than 120{\deg} between the two gas disks, and 40{\deg} between each gas disk and the stellar component. The star formation activity is enhanced at the interface of the two gas disks compared with the other regions within the same galaxy. Such systems illustrate that low-redshift galaxies can still experience multiple gas acquisition events, and provide a new view into the origins of galactic gas.