H i in isolated extremely metal-deficient galaxies

Abstract

We present Giant Metrewave Radio Telescope H i observations of two extremely metal-deficient (XMD) galaxies, UM 133 and SDSS J011914.27−093546.4, with no known nearby companions. Earlier H i observations of XMD galaxies have shown that disturbed H i morphologies and kinematics, generally related to tidal interaction with a companion, are common in them. However, some of these galaxies were already known to be in pairs before the H i observations. The two galaxies studied here were specifically selected because they do not have any known nearby companions. None the less, we find that both the galaxies have highly disturbed H i morphologies and velocity fields. These could have arisen from interactions with more distant companions than considered in our isolation criteria or merger with extremely gas-rich dwarf companions. It is also possible that distorted H i distributions of these XMD galaxies are the result of cold gas accretion from the intergalactic medium. Our observations provide further support to the idea that inflow of metal-poor gas from the outskirts of a galaxy to the central star-forming regions (in the case of interaction), or cold gas accretion is the probable cause for the observed low emission-line metallicities of XMD galaxies.