tokens: galaxies, not the lower z ones in our low-mass sample (see XXL paper XXVII). We label these two as BG? in the table. Removing all seven likely or possible contaminants, 8 all of which have s > 5 arcsec, then leaves us with 20 likely genuine matched low-mass emission-line objects (though alternate matches may still exist for a few of them, cf. XXL paper XXVII). The X-ray sources matched to these 20 emission-line galaxies lie in the range L Xs = 10 39.2 to 10 41.1 erg s −1 . The highest X-ray luminosities appear to (just) fit in the expected range, which cuts off at ∼10 41 erg s −1 (e.g. Mineo et al. 2012 ) if the extension of HMXBs into ULXs is included. In total, then, a reasonable number, ≃20, likely XRBs have been found, probably mostly HMXBs in low-mass star-forming galaxies. For these, there is no correlation between X-ray luminosity and emission-line luminosity, which can easily be explained if the X-rays are from individual single HMXBs while the line emission reflects the ISM conditions and star formation in the galaxy. It is difficult to relate our present results to those in the literature on the prevalence of HMXBs in brighter/more massive star-forming galaxies, for a number of reasons. In particular, we are able to detect only the brightest X-ray sources and have a flux limited rather than volume limited sample. Our nearest and faintest source is at 10 39.2 erg s −1 while at the redshift of our most distant matched low-mass galaxy ( z ≃ 0.1) the detection limit is approaching 10 41 erg s −1 . This can be contrasted with, for example, the general study of local star-forming galaxies by Mineo et al. ( 2012 ) who found about one HMXB for every 0.3 yr −1 of star formation, but with a detection limit 10 38 erg s −1 , considerably below our accessible limits. Using a reasonable slope of the HMXB luminosity function (e.g. Grimm et al. 2003 ), we would need to correct the numbers detected in even nearby redshift bins (say at z ≃ 0.03, where the effective limit is around 10 39.5 erg s −1 ) by an order of magnitude, and in our more distant bins we are in the tail of the LF, near the upper cut-off, requiring very large (around two orders of magnitude) and very uncertain corrections. The best we can probably say is that, given our 20 actual detections, we would expect perhaps of order 500 detections if we had a similar X-ray limit to Mineo et al. In addition, the intercomparison of SFRs is problematic: translating H α luminosities to total SFRs (e.g. Kennicutt 1994 ) involves numerous uncertain steps (e.g. use of a particular initial mass function) and Mineo et al. ( 2012 ) use a completely different method based on infrared and ultraviolet luminosities. If, for a concrete example, we simply translate H α luminosity to an ‘indicative’ SFR via Kennicutt ( 1983 )’s relation SFR ≃ L H α /(10 41 erg s −1 ) yr −1 , ignoring any systematics in this translation, 9 then the total indicative SFR summed over our 21 low-mass host galaxies (we exclude
ner_tags: O O O O O O O O O O O B-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation O B-Wavelength O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O B-Wavelength O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O B-Wavelength O B-Wavelength O O O O O O O O O O B-Wavelength O O O O O B-Wavelength O O O O O O O O O O O B-Wavelength O O O O O O O O O O O B-Wavelength O O O O B-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength O O O O O O O O O O O O O O O O O O O O B-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O B-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength O O B-Citation I-Citation I-Citation O O O O O O O O O B-Wavelength I-Wavelength O O O O O B-Citation I-Citation O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O B-Wavelength O B-Wavelength O O O O O O O O O B-Wavelength I-Wavelength O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O