Seeking large-scale magnetic fields in a pure-disk dwarf galaxy NGC 2976

TL;DR

This study investigates the magnetic field structure of the dwarf galaxy NGC 2976, revealing complex morphology influenced by gravitational interactions and environmental effects, with implications for galaxy magnetization and field generation mechanisms.

Contribution

It provides the first detailed magnetic field analysis of a pure-disk dwarf galaxy, highlighting the role of tidal interactions and environment in shaping magnetic structures.

Findings

Magnetic field strength is about 7 μG with an ordered component of 3 μG.

The magnetic field morphology includes a southern polarized ridge not solely due to dynamo processes.

NGC 2976 can magnetize its surroundings up to 5 kpc, influenced by tidal interactions.

Abstract

It is still unknown how magnetic field-generation mechanisms could operate in low-mass dwarf galaxies. Here, we present a detailed study of a nearby pure-disk dwarf galaxy NGC 2976. Unlike previously observed dwarf objects, this galaxy possesses a clearly defined disk. For the purpose of our studies, we performed deep multi-frequency polarimetric observations of NGC 2976 with the VLA and Effelsberg radio telescopes. Additionally, we supplement them with re-imaged data from the WSRT-SINGS survey. The magnetic field morphology discovered in NGC 2976 consists of a southern polarized ridge. This structure does not seem to be due to just a pure large-scale dynamo process (possibly cosmic-ray driven) at work in this object, as indicated by the RM data and dynamo number calculations. Instead, the field of NGC 2976 is modified by past gravitational interactions and possibly also by ram pressure inside the M 81 galaxy group environment. The estimates of total (7 muG) and ordered (3 muG) magnetic field strengths, as well as degree of field order (0.46), which is similar to those observed in spirals, suggest that tidally generated magnetized gas flows can further enhance dynamo action in the object. NGC 2976 is apparently a good candidate for the efficient magnetization of its neighbourhood. It is able to provide an ordered (perhaps also regular) magnetic field into the intergalactic space up to a distance of about 5 kpc. Tidal interactions (and possibly also ram pressure) can lead to the formation of unusual magnetic field morphologies (like polarized ridges) in galaxies out of the star-forming disks, which do not follow any observed component of the interstellar medium (ISM), as observed in NGC 2976. These galaxies are able to provide ordered magnetic fields far out of their main disks.