ViCTORIA project: The LOFAR view of environmental effects in Virgo cluster star-forming galaxies

Abstract

Context. Environmental effects such as ram pressure stripping (RPS) shape the evolution of galaxies in dense regions. Aims. We used the nearby Virgo cluster as a laboratory to study the environmental effects on the nonthermal components of star-forming galaxies. Methods. We constructed a sample of 17 RPS galaxies in the Virgo cluster and a statistical control sample of 119 nearby galaxies from the Herschel Reference Survey. All objects in these samples were detected in LOFAR 144 MHz observations and come with Hα and/or far-UV star formation rate (SFR) estimates. Results. We derived the radio–SFR relations, confirming a clearly super-linear slope of ≈1.4. We found that Virgo cluster RPS galaxies have radio luminosities that are a factor of 2−3 larger than galaxies in our control sample. We also investigated the total mass-spectral index relation, where we found a relation for the Virgo cluster RPS galaxies that is shifted to steeper spectral index values by 0.17 ± 0.06. Analyzing the spatially resolved ratio between the observed and the expected radio emission based on the hybrid near-UV + 100 μm SFR surface density, we generally observed excess radio emission all across the disk with the exception of a few leading-edge radio-deficient regions. Conclusions. The radio excess and the spectral steepening for the RPS sample could be explained by an increased magnetic field strength if the disk-wide radio enhancement is due to projection effects. For the galaxies that show the strongest radio excesses (NGC 4330, NGC 4396 and NGC 4522), a rapid decline in the SFR (tquench ≤ 100 Myr) could be an alternative explanation. We disfavor shock acceleration of electrons as a cause for the radio excess since it cannot easily explain the spectral steepening and radio morphology.