UGC 3672: An unusual merging triplet of gas-rich galaxies in the Lynx-Cancer void

TL;DR

UGC 3672 is a unique triplet of gas-rich, metal-poor dwarf galaxies aligned linearly within a common HI envelope in a low-density void, offering insights into galaxy formation and interactions in such environments.

Contribution

This study presents detailed HI and optical observations of a rare triplet of gas-rich dwarfs in a void, revealing their filamentary structure and potential formation pathways.

Findings

Triplet of gas-rich dwarfs aligned linearly with velocity continuity

Presence of a common HI envelope with filamentary tails and bridges

Implications for galaxy formation in low-density environments

Abstract

We present HI 21cm and optical observations of UGC 3672 which is located near the centre of the nearby Lynx-Cancer void. We find that UGC 3672 consists of an approximately linearly aligned triplet of gas rich dwarfs with large scale velocity continuity along the triplet axis. The faintest component of the triplet is extremely gas-rich (MHI/LB ~ 17) and also extremely metal deficient (12+log(O/H) ~ 7.0). The metallicity of this dwarf is close to the 'floor' observed in star forming galaxies. Low resolution HI images show that the galaxy triplet is located inside a common HI envelope, with fairly regular, disk like kinematics. At high angular resolution however, the gas is found to be confined to several filamentary tidal tails and bridges. The linear alignment of the galaxies, along with the velocity continuity that we observe, is consistent with the galaxies lying along a filament. We argue that the location of this highly unusual system in an extremely low density environment is not a coincidence, but is a consequence of structure formation proceeding more slowly and also probing smaller scales than in regions with average density. Our observations also indicate that wet mergers of galaxies flowing along filaments is a possible pathway for the formation of gas rich disks. The UGC 3672 system provides an interesting opportunity to study the kind of interactions typical between high redshift extremely gas rich unevolved small systems that lie at base of the hierarchical galaxy formation model.