Ultra Diffuse Galaxies in clusters : the peculiar gas loss of VCC 1964

TL;DR

This study investigates the gas loss and dynamical properties of the ultra diffuse galaxy VCC 1964 in a cluster, revealing gas displacement likely caused by ram pressure and suggesting a potential dark matter deficit.

Contribution

First detailed analysis of gas displacement and dynamics in a cluster UDG, combining HI and optical data to understand environmental effects on these galaxies.

Findings

VCC 1964 shows a 9 kpc offset between HI and optical components.

The galaxy exhibits a significant deviation from the Tully-Fisher relation.

Evidence suggests gas displacement due to ram pressure as it enters the cluster.

Abstract

Context : Ultra Diffuse Galaxies are low surface brightness systems which have been detected in HI in the field, where their line widths sometimes indicate significant dark matter deficits. They are rarely detected in HI in clusters, making their dynamical properties difficult to assess. The relation between field and cluster populations is unclear. Aims : Detecting UDGs entering a cluster could give important clues to their evolution, both in terms of their dynamics but also as to whether they are structurally similar - i.e. if cluster UDGs are generally the same as field UDGs except with less gas and an older stellar population. Methods : We use data from two deep Arecibo surveys, the Arecibo Galaxy Environment Survey and the Widefield Arecibo Virgo Environment Survey, to measure the gas content of the UDG-candidate VCC 1964. Optical properties are quantified from the Sloan Digital Sky Survey and DESI Legacy Surveys. Results : We find a significant 9 kpc offset between the HI and optical components of VCC 1964, no evidence of asymmetry in the HI, and only a modest deficiency level. This suggests a wholesale displacement of the gas content. The line width is 4-5 sigma deviant from the baryonic and over 6 sigma deviant from the optical forms of the Tully-Fisher relation. The optical component is blue and smooth. Conclusions : VCC 1964 is consistent with a UDG experiencing gas displacement due to ram pressure as it enters the cluster for the first time. Intriguingly, its dynamics imply a significant dark matter deficit, however we cannot rule out that this may be due to the gas being displaced out of equilibrium.