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

Journal
Date Issued
2021
Author(s)
Nwaokoro, E.
•
Phillipps, S.
•
Young, A. J.
•
Baldry, I.
•
•
Bremer, M. N.
•
Brown, M. J.I.
•
•
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.
•
•
Vignali, C.
DOI
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).
Volume
502
Issue
2
Start page
3101
Uri
Url
Issn Identifier
0035-8711
Rights
open.access
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