The H IX galaxy survey

III. The gas-phase metallicity in H I eXtreme galaxies^★

¹ Université de Strasbourg, CNRS, CDS, Observatoire astronomique de Strasbourg, UMR 7550, 67000 Strasbourg, France
e-mail: research@katha-lutz.de
² Centre for Astrophysics and Supercomputing, Swinburne University of Technology, PO Box 218, Hawthorn, VIC 3122, Australia
³ International Centre for Radio Astronomy Research (ICRAR), M468, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
⁴ Australian Research Council, Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia
⁵ Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4L8, Canada
⁶ Australia Telescope National Facility, CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710, Australia

Received: 23 August 2019
Accepted: 21 December 2019

Abstract

Context. This paper presents the analysis of optical integral field spectra for the H I eXtreme (H IX) galaxy sample. H IX galaxies host at least 2.5 times more atomic gas (H I) than expected from their optical R-band luminosity. Previous examination of their star formation activity and H I kinematics suggested that these galaxies stabilise their large H I 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.

Aims. In this paper we now turn to the gas-phase metallicity as well as stellar and ionised gas kinematics in H IX galaxies to gain insights into recent accretion of metal-poor gas or recent mergers.

Methods. We compare the stellar, ionised, and atomic gas kinematics, and examine the variation in the gas-phase metallicity throughout the stellar disc of H IX galaxies.

Results. 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 H I mass. Metallicity gradients are comparable to other less H I-rich, local star forming galaxies.

Conclusions. We conclude that H IX 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.