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Published April 1, 2009 | Published
Journal Article Open

Environmental effects in clusters: modified far-infrared-radio relations within Virgo Cluster galaxies

Abstract

We present a study on the effects of the intracluster medium (ICM) on the interstellar medium (ISM) of 10 Virgo Cluster galaxies using Spitzer far-infrared (FIR) and Very Large Array radio continuum imaging. Relying on the FIR-radio correlation within normal galaxies, we use our infrared data to create model radio maps, which we compare to the observed radio images. For six of our sample galaxies, we find regions along their outer edges that are highly deficient in the radio compared with our models. We also detect FIR emission slightly beyond the observed radio disk along these outer edges. 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, although the total 20 cm radio continuum in this region does not appear strongly enhanced. These characteristics seem consistent for other galaxies with radio polarization data in the literature. The strength of the radio deficit is inversely correlated with the time since peak pressure as inferred from stellar population studies and gas-stripping simulations, consistent with the strength of the radio deficit being a good indicator of the strength of the current ram pressure. 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 as observed for some of our galaxies. We propose that CR particles are also reaccelerated 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 precisely coincident enhancement in the total synchrotron power for these regions suggest shearing, and possibly mild compression of the magnetic field, as the ICM wind drags and stretches the leading edge of the ISM.

Additional Information

© 2009 The American Astronomical Society. Received 2008 June 9; accepted 2009 January 5; published 2009 March 24. We thank the anonymous referee for their useful suggestions that helped to improve the content and presentation of this paper. We are grateful to the SINGS team for producing high quality data sets used in this study. This work is based in part on observations made with the SST, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

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August 21, 2023
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