How the Intracluster Medium Affects the Far-Infrared--Radio Correlation within Virgo Cluster Galaxies

TL;DR

This study investigates how the intracluster medium influences the interstellar medium of Virgo cluster galaxies by analyzing deviations in the far-infrared--radio correlation, revealing effects of ram pressure and magnetic field interactions.

Contribution

It introduces a method to identify ICM effects on galaxies using FIR and radio data, highlighting the role of ram pressure in creating radio deficits and magnetic field distortions.

Findings

Radio deficits align with ICM ram pressure signatures.

Galaxies with deficits show enhanced global radio flux.

Magnetic field shear explains polarization and spectral index observations.

Abstract

We present a study on the effects of the intracluster medium (ICM) on the interstellar medium (ISM) of 10 Virgo cluster galaxies using {\it Spitzer} far-infrared (FIR) and VLA radio continuum imaging. Relying on the FIR-radio correlation {\it within} normal galaxies, we use our infrared data to create model radio maps which we compare to the observed radio images. For 6 of our sample galaxies we find regions along their outer edges that are highly deficient in the radio compared with our models. We believe these observations are the signatures of ICM ram pressure. For NGC 4522 we find the radio deficit region to lie just exterior to a region of high radio polarization and flat radio spectral index, however the total radio continuum in this region does not appear significantly enhanced. This scenario seems consistent for other galaxies with radio polarization data in the literature. We also find that galaxies having local radio deficits appear to have enhanced global radio fluxes. Our preferred physical picture is that the observed radio deficit regions arise from the ICM wind sweeping away cosmic-ray (CR) electrons and the associated magnetic field, thereby creating synchrotron tails observed for some of our galaxies. CR particles are also re-accelerated by ICM-driven shocklets behind the observed radio deficit regions which in turn enhances the remaining radio disk brightness. The high radio polarization and lack of coincidental signatures in the total synchrotron power in these regions arises from shear, and possibly mild compression, as the ICM wind drags and stretches the magnetic field.