Magnetic fields and gas in the cluster-influenced spiral galaxy NGC 4254 - II. Structures of magnetic fields

TL;DR

This study maps magnetic field structures in NGC 4254, revealing the influence of density waves, gas flows, and cluster interactions on magnetic field orientation, strength, and dynamo modes, with implications for galaxy evolution.

Contribution

It provides detailed magnetic field maps and analyzes the effects of cluster environment and gas dynamics on magnetic structures in NGC 4254, highlighting non-dynamo influences.

Findings

Magnetic field vectors vary dramatically, influenced by density waves and gas flows.

Total magnetic field strength correlates with star formation rate as a power-law.

Outer magnetic arms show strong, anisotropic magnetic fields modified by cluster interactions.

Abstract

The origin of asymmetric radio polarized emission and properties of magnetic fields in the Virgo Cluster spiral NGC4254 are investigated with help of "magnetic maps" presenting distributions of different magnetic field components over the entire galaxy, free of Faraday rotation and projection effects. We show that the dramatic variation of orientation of magnetic field vectors (from 0deg to more than 40deg) throughout the galaxy cannot arise from the dynamo process alone, but must be dominated by the effects like density waves and local gas flows. We determine within the galaxy the relation between the strength of total magnetic field and the local star-formation rate (SFR) as a power-law with an index of +0.18+-0.01. We find the opposite sense of relation of magnetic field regularity with SFR (-0.32+-0.03) and suggest that it results from efficient production of random field with rising turbulence in the regions with actively forming stars. The distribution of Faraday rotation measures in NGC4254 indicates a perturbed axisymmetrical mean-field dynamo mode or a mixture of axisymmetrical and bisymmetrical ones with regular field directed outwards the disk, which is contrary to most observed galaxies. The magnetic fields within two outer magnetic arms (shifted downstream of a density wave) are strong, up to 13muG in the regular field and 20muG in the total field. Our modeling of cluster influence on different magnetic field components indicates that within the outer magnetic arms the dynamo-induced magnetic fields are modified by stretching and shearing forces rather than by cluster ram pressure. Those forces, which are likely triggered by the galaxy's gravitational interaction, produce an anisotropic component of the regular field and enhance the polarized emission.(abridged)