Ram pressure stripping of the multiphase ISM in the Virgo cluster spiral galaxy NGC 4438

TL;DR

This study investigates how ram pressure stripping affects the multiphase interstellar medium in galaxy NGC 4438, revealing in situ electron re-acceleration and differential stripping of ionized and neutral gas in a cluster environment.

Contribution

It provides new insights into the multiphase ISM response to ram pressure stripping, including magnetic field behavior and ionized gas dynamics, in a galaxy affected by both tidal interaction and ram pressure.

Findings

Extraplanar radio emission extends twice as far as other tracers.

Spectral index does not steepen, indicating electron re-acceleration.

Ionized gas is more efficiently stripped than neutral gas.

Abstract

Ram pressure stripping of the multiphase ISM is studied in the perturbed Virgo cluster spiral galaxy NGC 4438. This galaxy underwent a tidal interaction ~100 Myr ago and is now strongly affected by ram pressure stripping. Deep VLA radio continuum observations at 6 and 20 cm are presented. We detect prominent extraplanar emission to the west of the galactic center, which extends twice as far as the other tracers of extraplanar material. The spectral index of the extraplanar emission does not steepen with increasing distance from the galaxy. This implies in situ re-acceleration of relativistic electrons. The comparison with multiwavelength observations shows that the magnetic field and the warm ionized interstellar medium traced by Halpha emission are closely linked. The kinematics of the northern extraplanar Halpha emission, which is ascribed to star formation, follow those of the extraplanar CO emission. In the western and southern extraplanar regions, the Halpha measured velocities are greater than those of the CO lines. We suggest that the ionized gas of this region is excited by ram pressure. The spatial and velocity offsets are consistent with a scenario where the diffuse ionized gas is more efficiently pushed by ram pressure stripping than the neutral gas. We suggest that the recently found radio-deficient regions compared to 24 mum emission are due to this difference in stripping efficiency.