The Chandra Deep Field-North survey. VII. X-ray emission from Lyman break galaxies

We present results from stacking analyses, using the I Ms Chandra Deep Field-North data, that constrain the X-ray emission of Lyman break galaxies at z approximate to 2-4. Stacking the counts from 24 individually undetected Lyman break galaxies located within the Hubble Deep Field-North, we have obtained average detections of these objects in the resulting 0.5-8.0 and 0.5-2.0 keV images; these images have effective exposure times of 22.4 Ms (260 days). Monte Carlo testing empirically shows the detections to be highly significant. The average rest-frame 2-8 keV luminosity of a Lyman break galaxy is derived to be approximate to3.2 x 10(41) ergs s(-1), comparable to that of the most X-ray luminous starbursts in the local universe. The observed ratio of X-ray to B-band luminosity is somewhat, but not greatly, higher than that seen from local starbursts. The X-ray emission probably arises from a combination of high-mass X-ray binaries, "super-Eddington" X-ray sources, and low-luminosity active galactic nuclei.