We present an analysis of the X-ray emission of a large sample of z \sim 3 Lyman break galaxies ( LBGs ) , based on Chandra /ACIS observations of several LBG survey fields .
A total of twenty-four LBGs are directly detected in the X-ray , approximately doubling the number of known detections .
Thirteen of the LBGs have optical spectroscopic signatures of AGN activity , but almost all the other X-ray detections are also likely to host an accreting black hole based on their X-ray properties .
The AGN exhibit a wide range in X-ray luminosity , from weak Seyferts to bright QSOs .
Optical spectroscopy identified approximately 1/3 of the X-ray detected sources as broad line QSOs , 1/3 as narrow line AGN and 1/3 as normal star forming LBGs .
The fraction of X-ray detected LBGs is 3 per cent , much lower than has been found for submm selected galaxies .
Two galaxies have X-ray luminosities , spectra and f _ { \mathrm { X } } / f _ { \mathrm { opt } } values that are consistent with emission from star formation processes and are identified as candidate X-ray bright , pure starburst galaxies at z \sim 3 .
If powered solely by star formation the sources would have SFRs of 300–500 \thinspace M _ { \odot } yr ^ { -1 } .
X-ray spectral analysis of the LBGs shows a mean photon index of \Gamma = 1.96 , similar to local AGN .
There is evidence for absorption in at least 40 per cent of the objects .
Significantly more absorption is evident in the narrow line AGN , which is consistent with AGN unification schemes .
After correction for absorption the narrow and broad line objects show the same average luminosity .
X-ray detected LBGs spectroscopically classified as normal galaxies , however , are less luminous in both soft and hard X-ray bands indicating that the host galaxy is outshining any optical AGN signature .
Turning to the X-ray emission from LBGs without direct detections , stacking the X-ray flux in the two deepest Chandra fields under consideration ( the HDF-N and GWS ) produced significant detections in each , although the GWS result was marginal .
The detection in the HDF-N gives an X-ray derived SFR of 42.4 \pm 7.8 M _ { \odot } yr ^ { -1 } per LBG and , by comparing with the UV SFR , the implied UV extinction correction is 4.1 \pm 0.8 .
The LBG sample was split into three bins based on UV magnitude to examine the correlation between UV and X-ray emission : for the limited statistics available there was no evidence of any correlation .