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

*Corresponding author for this work

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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).

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

Bibliographical note

Copyright 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


  • galaxies: active
  • galaxies: star formation
  • X-rays: galaxies


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