The ALMA Detection of Extraplanar 13 CO in a Ram-pressure-stripped Galaxy and Its Implication

Abstract

NGC 4522 is a Virgo spiral that is currently undergoing active ram pressure stripping. In previous single-dish observations, 12 CO emission was detected outside of the stellar disk, some of which coincides with the extraplanar H i gas and H α patches. The extraplanar gas identified in multi-wavelength data makes this galaxy an ideal case to study the impact of pressure due to the cluster medium on the interstellar gas of various phases. In this Letter, we present the high-resolution 12 CO(1–0) and 13 CO(1–0) data of NGC 4522 obtained using the Atacama Large Millimeter/submillimeter Array (ALMA). In particular, we report here the extraplanar 13 CO detection that has never before been seen in ram-pressure-stripped galaxies. As the main donor of 13 C in the interstellar medium is evolved stars, the presence of 13 CO strongly suggests that heavy elements likely originated from the galactic disk, not from the newly formed stars in situ. Even though it is still inconclusive whether it is stripped in atomic form or as molecules, this study provides evidence for the ram pressure stripping of heavy elements, which can chemically enrich the halo gas, and potentially the intracluster medium, in the case that they are pushed strongly enough to escape the galaxy.