GAMA/XXL: X-ray point sources in low-luminosity galaxies in the GAMA G02/XXL-N field. Issue 2 (29th January 2021)

• Record Type: Journal Article
• Authors: 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
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 502:Issue 2(2021)
• Page Start: 3101
• Page End: 3112
• Publication Date: 2021-01-29
• Subjects: galaxies: active -- galaxies: star formation -- X-rays: galaxies; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stab242
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: 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 $M_* \lesssim 10^{9.5}\, \mathrm{M}_{\odot }$ ). 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 10 40.3 erg s −1 ).