Radio Continuum Observations of the Virgo Cluster Spiral NGC 4522: The Signature of Ram Pressure

Abstract

Radio continuum observations at 20 and 6 cm of the highly inclined Virgo spiral galaxy NGC 4522 are presented. Both 20 and 6 cm total emission distributions are asymmetric with an extended component to the west, where extraplanar atomic gas and Hα emission are found. The 6 cm polarized emission is located at the eastern edge of the galactic disk. Its peak is located about 1 kpc to the east of the total emission peak. We argue that this phenomena is a characteristic feature for cluster galaxies that are experiencing significant pressure from the intracluster medium. Polarized radio continuum emission is thus a powerful tool to detect interactions of spiral galaxies with the cluster ICM. The degree of polarization decreases from the east to the west. The flattest spectral index between 20 and 6 cm coincides with the peak of the 6 cm polarized emission. These findings are consistent with a picture of a large-scale shock due to ram pressure located at the east of the galaxy where cosmic rays are accelerated. We conclude that it is likely that the galaxy experiences active ram pressure.