Ultraviolet tails and trails in cluster galaxies: A sample of candidate gaseous stripping events in Coma

TL;DR

This study identifies and analyzes 13 candidate gas stripping events in Coma cluster galaxies using ultraviolet, optical, and H-alpha imaging, revealing that gas stripping and star formation in stripped material are common in rich clusters.

Contribution

It presents a new sample of gaseous stripping candidates in Coma, showing their distribution, morphology, and the short-lived nature of these events, supported by observational and simulation data.

Findings

Stripping events are more common closer to the cluster center.

Most stripping occurs on first infall, within ~1 Mpc, lasting about 500 Myr.

Stripping is associated with star formation in the stripped gas.

Abstract

We have used new deep observations of the Coma cluster from GALEX to identify 13 star-forming galaxies with asymmetric morphologies in the ultraviolet. Aided by optical broad-band and H-alpha imaging, we interpret the asymmetric features as being due to star formation within gas stripped from the galaxies by interaction with the cluster environment. The selected objects display a range of structures from broad fan-shaped systems of filaments and knots (`jellyfish') to narrower and smoother tails extending up to 100 kpc in length. Some of the features have been discussed previously in the literature, while others are newly identified here. As an ensemble, the candidate stripping events are located closer to the cluster centre than other star-forming galaxies; their radial distribution is similar to that of all cluster members, dominated by passive galaxies. The fraction of blue galaxies which are undergoing stripping falls from 40% in the central 500 kpc, to less than 5% beyond 1 Mpc. We find that tails pointing away from (i.e. galaxies moving towards) the cluster centre are strongly favoured (11/13 cases). From the small number of `outgoing' galaxies with stripping signatures we conclude that the stripping events occur primarily on first passage towards the cluster centre, and are short-lived compared to the cluster crossing time. Using infall trajectories from simulations, the observed fraction of blue galaxies undergoing stripping can be reproduced if the events are triggered at a threshold radius of ~1 Mpc and detectable for ~500 Myr. HST images are available for two galaxies from our sample and reveal compact blue knots coincident with UV and H-alpha emission, apparently forming stars within the stripped material. Our results confirm that stripping of gas from infalling galaxies, and associated star formation in the stripped material, is a widespread phenomenon in rich clusters.