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

E. Nwaokoro, S. Phillipps, A. J. Young, I. Baldry, A. Bongiorno, M. N. Bremer, M. J.I. Brown, L. Chiappetti, R. De Propris, S. P. Driver, A. Elyiv, S. Fotopoulou, P. A. Giles, A. M. Hopkins, B. Maughan, S. McGee, F. Pacaud, M. Pierre, M. Plionis, B. M. PoggiantiC. Vignali

Research output: Contribution to journalArticlepeer-review

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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∗ ≲ 109.5, M⊙). 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).

Original languageEnglish
Pages (from-to)3101-3112
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Volume502
Issue number2
DOIs
Publication statusPublished - 1 Apr 2021

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