NGC 3314a/b and NGC 3312: Ram pressure stripping in Hydra I Cluster substructure

TL;DR

This study provides multi-wavelength evidence of ram pressure stripping in specific galaxies within the Hydra I Cluster, revealing details about gas removal, star formation, and galaxy motion relative to the cluster center.

Contribution

It offers new detailed observations of ram pressure effects in Hydra I Cluster galaxies, including quantification of stripped gas and insights into galaxy trajectories and cluster substructure.

Findings

NGC 3312 and NGC 3314a have 8-35% of their gas stripped.

Stripped gas extends 30-60 kpc and forms stars at ~0.5 M_Sun/yr.

Galaxies are likely moving towards us, on an outfall trajectory from the cluster.

Abstract

Cluster substructure and ram pressure stripping in individual galaxies are among the primary evidence for the ongoing growth of galaxy clusters as they accrete galaxies and groups from their surroundings. We present a multi-wavelength study of the center of the Hydra I galaxy cluster, including exquisite new MeerKAT HI and DECam Halpha imaging which reveal conclusive evidence for ram pressure stripping in NGC 3312, NGC 3314a and NGC 3314b through compressed HI contours, well-defined HI tails, and ongoing star formation in the stripped gas. In particular, we quantify the stripped material in NGC 3312 and NGC 3314a, which makes up between 8% and 35% of the gas still in the disk, is forming stars at ~0.5 M_Sun yr^-1, and extends ~30-60 kpc from the main disk. The estimated stellar mass in the tails is an order of magnitude less than the HI mass. A fourth "ring" galaxy at the same velocity does not show signs of ram pressure in HI. In addition, we use the HI and stellar morphologies, combined with a Beta model of the hot intracluster medium, to constrain the real distances of the galaxies to the cluster center, and we use the chance alignment of NGC 3314b behind NGC 3314a to break the degeneracy between whether the galaxies are in front or in back of the cluster. The drag seen in the HI tails supports our preferred scenario that NGC 3312 and NGC 3314a are moving towards us as part of a foreground substructure which has already passed its pericenter and is on "out fall" from the cluster. The high surviving HI content of the galaxies may suggest that the substructure/intragroup medium can protect them from the harshest effects of ram pressure, or that in fact the galaxies are on more tangential orbits.