Chemical Abundances of Seven Irregular and Three Tidal Dwarf Galaxies in the M81 Group

TL;DR

This study measures nebular abundances in 10 dwarf galaxies of the M81 Group, revealing that most follow the metallicity-luminosity relation, but some tidal dwarf candidates deviate, indicating recent formation from enriched gas.

Contribution

First detailed nebular abundance analysis of multiple dwarf galaxies in the M81 Group, including newly reported data and insights into tidal dwarf galaxy formation.

Findings

Most galaxies follow the metallicity-luminosity relation.

Three candidate tidal dwarf galaxies deviate from this relation.

Tidal dwarf candidates likely formed from enriched gas stripped during interactions.

Abstract

We have derived nebular abundances for 10 dwarf galaxies belonging to the M81 Group, including several galaxies which do not have abundances previously reported in the literature. For each galaxy, multiple H \ii regions were observed with GMOS-N at the Gemini Observatory in order to determine abundances of several elements (oxygen, nitrogen, sulfur, neon, and argon). For seven galaxies, at least one H \ii region had a detection of the temperature sensitive [OIII] $\lambda$4363 line, allowing a "direct" determination of the oxygen abundance. No abundance gradients were detected in the targeted galaxies and the observed oxygen abundances are typically in agreement with the well known metallicity-luminosity relation. However, three candidate "tidal dwarf" galaxies lie well off this relation, UGC 5336, Garland, and KDG 61. The nature of these systems suggests that UGC 5336 and Garland are indeed recently formed systems, whereas KDG 61 is most likely a dwarf spheroidal galaxy which lies along the same line of sight as the M81 tidal debris field. We propose that these H \ii regions formed from previously enriched gas which was stripped from nearby massive galaxies (e.g., NGC 3077 and M81) during a recent tidal interaction.