CHANG-ES VII: Magnetic outflows from the Virgo cluster galaxy NGC 4388

TL;DR

This study uses new radio observations to analyze magnetic outflows and halo features in the Virgo galaxy NGC 4388, revealing insights into galactic winds, magnetic field structure, and ICM interactions.

Contribution

First detection of southern outflow in NGC 4388 and analysis of magnetic field features related to ram pressure effects.

Findings

Extended polarized emission blobs with perpendicular magnetic fields

Mean outflow velocity of cosmic ray electrons is 270 km/s

Halo features suggest ICM ram pressure is consistent with X-ray and SZ data

Abstract

We investigate the effects of ram pressure on the ordered magnetic field of a galaxy hosting a radio halo and strong nuclear outflows. New radio images in total and polarized intensity of the edge-on Virgo galaxy NGC\,4388 were obtained within the CHANG-ES EVLA project. The unprecedented noise level reached allows us to detect striking new features of the ordered magnetic field. The nuclear outflow extends far into the halo to about 5\,kpc from the center and is spatially correlated with the $\rm{H}\alpha$ and X-ray emission. For the first time, the southern outflow is detected. Above and below both spiral arms we find extended blobs of polarized emission with an ordered field oriented perpendicular to the disk. The synchrotron lifetime of the cosmic ray electrons (CREs) in these regions yields a mean outflow velocity of $(270\pm70)\kms$, in agreement with a galactic wind scenario. The observed symmetry of the polarized halo features in NGC 4388 excludes a compression of the halo gas by the ram pressure of the intra-cluster medium (ICM). The assumption of equilibrium between the halo pressure and the ICM ram pressure yields an estimate of the ICM density that is consistent with both the ICM density derived from X-ray observations and the recent \textit{Planck} Sunyaev-Zel'dovich measurements. The detection of a faint radio halo around cluster galaxies could thus be used for an estimate of ICM ram pressure.