The starburst nature of Lyman break galaxies: Testing ultraviolet extinction with X-rays

We derive the bolometric to-X-ray correlation for a local sample of normal and starburst galaxies and use it, in combination with several UV reddening schemes, to predict the 2 8 keV X-ray luminosity for a sample of 24 Lyman break galaxies in the Hubble Deep Field and Chandra Deep Field North. We find that the mean X-ray luminosity, as predicted from the Meurer UV reddening relation for starburst galaxies, agrees extremely well with the Brandt stacking analysis. This provides additional evidence that Lyman break galaxies can be considered as scaled-up local starbursts, and that the locally derived starburst UV reddening relation may be a reasonable tool for estimating the UV extinction at high redshift. Our analysis shows that the Lyman break sample cannot have far-IR to far-UV flux ratios similar to nearby ultraluminous infrared galaxies, since this would predict a mean X-ray luminosity 100 times larger than observed, as well as far-IR luminosities large enough to be detected in the submillimeter. We calculate the UV reddening expected from the Calzetti effective starburst attenuation curve and the radiative transfer models of Witt & Gordon for low-metallicity dust in a shell geometry with homogeneous or clumpy dust distributions and find that all are consistent with the observed X-ray emission. Finally, we show that the mean X-ray luminosity of the sample would be underpredicted by a factor of 6 if the far-UV is unattenuated by dust.