Dwarfs walking in a row. The filamentary nature of the NGC3109 association

TL;DR

This study reveals that the NGC3109 dwarf galaxy association forms a highly elongated, filamentary structure with a coherent velocity gradient, likely resulting from tidal interactions or filamentary accretion.

Contribution

It provides a new, detailed analysis of the spatial and velocity structure of the NGC3109 association, including the addition of Leo P as a member, highlighting its ordered, filamentary nature.

Findings

The association is a tight, elongated structure within ~100 kpc in width.

Galaxies show a velocity gradient with a total amplitude of 43 km/s/Mpc.

Leo P is likely a member of the NGC3109 association.

Abstract

We re-consider the association of dwarf galaxies around NGC3109, whose known members were NGC3109, Antlia, Sextans A and Sextans B, based on a new updated list of nearby galaxies and the most recent data. We find that the original members of the NGC3109 association, together with the recently discovered and adjacent dwarf irregular Leo P, form a very tight and elongated configuration in space. All these galaxies lie within ~100 kpc of a line that is ~1070 kpc long, from one extreme (NGC3109) to the other (Leo P), and they show a gradient in the Local Group standard of rest velocity with a total amplitude of 43 km/s Mpc and a r.m.s. scatter of just 16.8 km/s. It is shown that the reported configuration is exceptional given the known dwarf galaxies in the Local Group and its surroundings. We conclude that (a) Leo P is likely an additional member of the NGC3109 association, and (b) the association is highly ordered in space and velocity, and it is very elongated, suggesting that it has been originated by a tidal interaction or it was accreted as a filamentary sub-structure.