Nwaokoro, E.; Phillipps, S.; Young, A. J.; Baldry, I.; Bongiorno, A.; Bremer, M. N.; Brown, M. J. I.; Chiappetti, L.; De Propris, R.; Driver, S. P.; Elyiv, A.; Fotopoulou, S.; Giles, P. A.; Hopkins, A. M.; Maughan, B.; McGee, S.; Pacaud, F.; Pierre, M.; Plionis, M.; Poggianti, B. M.; Vignali, C.
Monthly Notices of the Royal Astronomical Society, Vol. 502, p.3101-3112
Publication year: 2021

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 M109.5M ). 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).

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