GAMA/XXL: X-ray point sources in low-luminosity galaxies in the GAMA G02/XXL-N field

Relatively few X-ray sources are known that have low-mass galaxies as hosts. This is an important restriction on studies of active galactic nuclei (AGNs), hence black holes, and of X-ray binaries (XRBs) in low-mass galaxies; addressing it requires very large samples of both galaxies and X-ray sources. Here, we have matched the X-ray point sources found in the XXL-N field of the XXL survey (with an X-ray flux limit of ~6 × 10-15 erg s-1 cm-2 in the [0.5-2] keV band) to galaxies with redshifts from the Galaxy And Mass Assembly (GAMA) G02 survey field (down to a magnitude limit r = 19.8) in order to search for AGNs and XRBs in GAMA galaxies, particularly those of low optical luminosity or stellar mass (fainter than Mr = -19 or M∗≲109.5M⊙ ). Out of a total of 1200 low-mass galaxies in the overlap region, we find a total of 28 potential X-ray source hosts, though this includes possible background contaminants. From a combination of photometry (optical and infrared colours), positional information, and optical spectra, we deduce that most of the ≃20 X-ray sources genuinely in low-mass galaxies are high-mass X-ray binaries in star-forming galaxies. None of the matched sources in a low-mass galaxy has a BPT classification as an AGN, and even ignoring this requirement, none passes both criteria of close match between the X-ray source position and optical galaxy centre (separation ≤3 arcsec) and high [O III] line luminosity (above 1040.3 erg s-1). | External Organisations University of Bristol; Astronomical Observatory of Padua; Tulane University; Johns Hopkins University; National Institute for Astrophysics; Osservatorio Astronomico Roma; Indiana University Bloomington; Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna; University of Turku; University of Liege; NASU - Main Astronomical Observatory; University of Bologna; University of Geneva; Durham University; Macquarie University; University of Birmingham; Argelander Institut für Astronomie; University of Bonn; Université Paris Diderot (Paris 7); Aristotle University of Thessaloniki; Instituto Nacional de Astrofisica Optica y Electronica | Associated Persons E. Nwaokoro (Creator); S Phillipps (Creator); Alyssa J. Young (Creator); I. K. Baldry (Creator); A. Bongiorno (Creator); Malcolm N. Bremer (Creator); Jeffrey M. Brown (Creator); L. Chiappetti (Creator); Roberto De Propris (Creator); A. Elyiv (Creator); S. Fotopoulou (Creator); Paul A. Giles (Creator); Andrew M. Hopkins (Creator); B. Maughan (Creato