Very metal-poor galaxies: ionized gas kinematics in nine objects

TL;DR

This study investigates the ionized gas kinematics in nine extremely metal-deficient galaxies, revealing disturbed gas morphology and evidence of interactions or mergers that likely trigger star formation, providing insights into early galaxy evolution.

Contribution

It offers new observational data on gas kinematics in XMD galaxies, highlighting the role of interactions in star formation, and includes analysis of two additional dwarf galaxies affected by mergers.

Findings

Most XMD dwarfs show disturbed gas morphology and kinematics.

Interactions and mergers are linked to enhanced star formation.

Data for two dwarf galaxies suggest interaction-induced star formation.

Abstract

The study of ionized gas morphology and kinematics in nine eXtremely Metal-Deficient (XMD) galaxies with the scanning Fabry-Perot interferometer on the SAO 6-m telescope is presented. Some of these very rare objects (with currently known range of O/H of 7.12 < 12+log(O/H) < 7.65, or Zo/35 < Z < Zo/10) are believed to be the best proxies of `young' low-mass galaxies in the high-redshift Universe. One of the main goals of this study is to look for possible evidence of star formation (SF) activity induced by external perturbations. Recent results from HI mapping of a small subsample of XMD star-forming galaxies provided confident evidence for the important role of interaction-induced SF. Our observations provide complementary or new information that the great majority of the studied XMD dwarfs have strongly disturbed gas morphology and kinematics or the presence of detached components. We approximate the observed velocity fields by simple models of a rotating tilted thin disc, which allow us the robust detection of non-circular gas motions. These data, in turn, indicate the important role of current/recent interactions and mergers in the observed enhanced star formation. As a by-product of our observations, we obtained data for two LSB dwarf galaxies: Anon J012544+075957 that is a companion of the merger system UGC 993, and SAO 0822+3545 which shows off-centre, asymmetric, low SFR star-forming regions, likely induced by the interaction with the companion XMD dwarf HS 0822+3542.