Using the XMM-Newton Slew Survey , we construct a hard-band selected sample of low-luminosity Galactic X-ray sources .
Two source populations are represented , namely coronally-active stars and binaries ( ASBs ) and cataclysmic variables ( CVs ) , with X-ray luminosities collectively spanning the range 10 ^ { 28 - 34 } erg s ^ { -1 } ( 2–10 keV ) .
We derive the 2–10 keV X-ray luminosity function ( XLF ) and volume emissivity of each population .
Scaled to the local stellar mass density , the latter is found to be 1.08 \pm 0.16 \times 10 ^ { 28 } ~ { } erg~ { } s ^ { -1 } ~ { } M _ { \odot } ^ { -1 } and 2.5 \pm 0.6 \times 10 ^ { 27 } ~ { } erg~ { } s ^ { -1 } ~ { } M _ { \odot } ^ { -1 } , for the ASBs and CVs respectively , which in total is a factor 2 higher than previous estimates .
We employ the new XLFs to predict the X-ray source counts on the Galactic plane at l = 28.5 ^ { \circ } and show that the result is consistent with current observational constraints .
The X-ray emission of faint , unresolved ASBs and CVs can account for a substantial fraction of the Galactic ridge X-ray emission ( GRXE ) .
We discuss a model in which \sim 80 per cent of the 6–10 keV GRXE intensity is produced in this way , with the remainder attributable to X-ray scattering in the interstellar medium and/or young Galactic source populations .
Much of the hard X-ray emission attributed to the ASBs is likely to be produced during flaring episodes .