The H IX galaxy survey III: The gas-phase metallicity in HI eXtreme
  galaxies
  This paper presents the analysis of optical integral field spectra for the HI
eXtreme (HIX) galaxy sample. HIX galaxies host at least 2.5 times more atomic
gas (HI) than expected from their optical R-band luminosity. Previous
examination of their star formation activity and HI kinematics suggested that
these galaxies stabilise their large HI discs (radii up to 94 kpc) against star
formation due to their higher than average baryonic specific angular momentum.
A comparison to semi-analytic models further showed that the elevated baryonic
specific angular momentum is inherited from the high spin of the dark matter
host. In this paper we now turn to the gas-phase metallicity as well as stellar
and ionised gas kinematics in HIX galaxies to gain insights into recent
accretion of metal-poor gas or recent mergers. We compared the stellar,
ionised, and atomic gas kinematics, and examine the variation in the gas-phase
metallicity throughout the stellar disc of HIX galaxies. We find no indication
for counter-rotation in any of the components, the central metallicities tend
to be lower than average, but as low as expected for galaxies of similar HI
mass. Metallicity gradients are comparable to other less HI-rich, local star
forming galaxies. We conclude that HIX galaxies show no conclusive evidence for
recent major accretion or merger events. Their overall lower metallicities are
likely due to being hosted by high spin halos, which slows down their evolution
and thus the enrichment of their interstellar medium.
