The magnetic field structure in NGC 253 in presence of a galactic wind

TL;DR

This study uses radio polarimetry to analyze the magnetic field structure and cosmic-ray-driven galactic wind in NGC 253, revealing an X-shaped magnetic field and a significant galactic wind with a bulk speed of about 300 km/s.

Contribution

It provides detailed magnetic field decomposition and evidence of a galactic wind in NGC 253, enhancing understanding of magnetic field configurations in edge-on galaxies.

Findings

Detection of a galactic wind with ~300 km/s speed.

Identification of an X-shaped poloidal magnetic field.

Confirmation of an antisymmetric magnetic field parity.

Abstract

We present radio continuum polarimetry observations of the nearby edge-on galaxy NGC 253 which possesses a very bright radio halo. Using the vertical synchrotron emission profiles and the lifetimes of cosmic-ray electrons, we determined the cosmic-ray bulk speed as (300+/-30) km/s, indicating the presence of a galactic wind in this galaxy. The large-scale magnetic field was decomposed into a toroidal axisymmetric component in the disk and a poloidal component in the halo. The poloidal component shows a prominent X-shaped magnetic field structure centered on the nucleus, similar to the magnetic field observed in other edge-on galaxies. Faraday rotation measures indicate that the poloidal field has an odd parity (antisymmetric). NGC 253 offers the possibility to compare the magnetic field structure with models of galactic dynamos and/or galactic wind flows.