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 journalArticle (Academic Journal)peer-review

Abstract

Relatively few X-ray sources are known which have low mass galaxies as hosts. This is an important restriction on studies of Active Galactic Nuclei (AGN), hence black holes, and of X-ray binaries (XRBs) in low mass galaxies; addressing it requires very large samples of both galaxies and of 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 ∼ 6 × 10−15 erg s−1 cm−2 in the [0.5-2] keV band) to galaxies with redshifts from the GAMA G02 survey field (down to a magnitude limit r = 19.8) in order to search for AGN 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 infra-red 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 (HMXBs) 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”) and high [O III] line luminosity (above 1040.3 erg/s).
Original languageEnglish
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Publication statusAccepted/In press - 26 Jan 2021

Keywords

  • X-RAYS, GALAXIES
  • galaxies : active
  • galaxies: star formation

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