Formation of an ultra-diffuse galaxy in the stellar filaments of NGC3314A: caught in act?

TL;DR

This study reports the discovery of an ultra-diffuse galaxy, UDG32, within stellar filaments near NGC3314A, suggesting it may have formed from filament material, possibly through tidal interactions, in the Hydra I cluster.

Contribution

First identification of an ultra-diffuse galaxy within stellar filaments, proposing a possible tidal formation scenario based on observed properties and spatial coincidence.

Findings

UDG32 is one of the faintest and most diffuse galaxies in Hydra I.

UDG32's properties suggest a tidal origin, possibly formed from stellar filaments.

Spatial coincidence hints at formation from filament material, not projection effects.

Abstract

The VEGAS imaging survey of the Hydra I cluster reveals an extended network of stellar filaments to the south-west of the spiral galaxy NGC3314A. Within these filaments, at a projected distance of ~40 kpc from the galaxy, we discover an ultra-diffuse galaxy (UDG) with a central surface brightness of $\mu_{0,g}\sim26$ mag arcsec$^{-2}$ and effective radius $R_e\sim3.8$ kpc. This UDG, named UDG32, is one of the faintest and most diffuse low-surface brightness galaxies in the Hydra~I cluster. Based on the available data, we cannot exclude that this object is just seen in projection on top of the stellar filaments, thus being instead a foreground or background UDG in the cluster. However, the clear spatial coincidence of UDG32 with the stellar filaments of NGC3314A suggests that it might have formed from the material in the filaments, becoming a detached, gravitationally bound system. In this scenario, the origin of UDG32 depends on the nature of the stellar filaments in NGC3314A, which is still unknown. They could result from ram-pressure stripping or have a tidal origin. In this letter, we focus on the comparison of the observed properties of the stellar filaments and UDG32, and speculate about their possible origin. The relatively red color ($g-r=0.54 \pm 0.14$~mag) of the UDG, similar to that of the disk in NGC3314A, combined with an age older than 1Gyr, and the possible presence of a few compact stellar systems, all point towards a tidal formation scenario inferred for the UDG32.