The source of energetic photons that heated and reionized the early Universe remains uncertain .
Early galaxies had low metallicity and recent population synthesis calculations suggest that the number and luminosity of high-mass X-ray binaries are enhanced in star-forming galaxies with low metallicity , offering a potentially important and previously overlooked source of heating and reionization .
Lyman break analogue ( LBA ) galaxies are local galaxies that strongly resemble the high-redshift , star-forming Lyman Break Galaxies and have been suggested as local analogues to these metal-deficient galaxies found in the early Universe .
We studied a sample of ten LBAs in order to measure the relation between star formation rate and X-ray luminosity .
We found that for LBAs with metallicities in the range 12 + \log _ { 10 } ( { O / H } ) = 8.15 - 8.80 , the L _ { X } - SFR relation was \log _ { 10 } ( L _ { X } / { SFR } { [ erg s ^ { -1 } M _ { \sun } ^ { -1 } yr ] } ) = 39.85 ( \pm 0 % .10 ) in the 0.5 - 8 keV band with a dispersion of \sigma = 0.25 dex .
This is an enhancement of nearly a factor of 2 in the L _ { 0.5 - 8 \text { keV } } –SFR relation relative to results for nearby , near-solar metallicity galaxies .
The enhancement is significant at the 98.2 % level ( 2.4 \sigma ) .
Our enhanced L _ { X } / { SFR } relation is consistent with the metallicity-dependent predicted value from population synthesis models .
We discuss the possibility of a L _ { X } –SFR–Metallicity plane for star-forming galaxies .
These results are important to our understanding of reionization and the formation of early galaxies .