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Durham University

Department of Physics

Staff profile

Publication details for Prof David Alexander

Lehmer, B.D., Brandt, W.N., Alexander, D.M., Bauer, F.E., Conselice, C.J., Dickinson, M.E., Giavalisco, M., Grogin, N.A., Koekemoer, A.M., Lee, K.-S., Moustakas, L.A. & Schneider, D.P. (2005). X-Ray Properties of Lyman Break Galaxies in the Great Observatories Origins Deep Survey. Astronomical Journal 129(1): 1-8.

Author(s) from Durham


We constrain the X-ray emission properties of Lyman break galaxies (LBGs) at z~3-6 using the ~2 Ms Chandra Deep Field North and ~1 Ms Chandra Deep Field South. Large samples of LBGs were discovered using the Hubble Space Telescope as part of the Great Observatories Origins Deep Survey (GOODS). Deep optical and X-ray imaging over the GOODS fields have allowed us to place the most significant constraints on the X-ray properties of LBGs to date. Mean X-ray properties of 449, 1734, 629, and 247 LBGs with z~3, 4, 5, and 6, respectively, were determined using stacking techniques. When stacked, we detect X-ray emission from LBGs at z~3 (~7 sigma) and from an optically bright subset (brightest 25%) of LBGs at z~4 (~3 sigma) the latter is the highest redshift detection yet for ``normal'' galaxies in the X-ray band. The effective exposure times for these stacked observations are ~0.7 and 0.5 Gs, respectively. The derived average rest-frame 2.0-8.0 keV luminosities are 1.5×1041 and 1.4×1041 ergs s-1, respectively. X-ray emission from these LBGs is likely due to high-mass X-ray binaries and Type II supernovae; the corresponding star formation rates are ~10-30 Msolar yr-1. The X-ray-to-B-band mean luminosity ratio (LX/LB) at z~3 is somewhat elevated with respect to that measured for starburst galaxies in the local universe (significance ~3 sigma). When stacking full samples of LBGs at z~4, 5, and 6, we do not obtain significant detections (<3 sigma) and derive rest-frame 2.0-8.0 keV luminosity upper limits (3 sigma) of 0.9, 2.8, and 7.1 × 1041 ergs s-1, respectively. These upper limits constrain any widespread active galactic nucleus (AGN) activity in these objects to be modest at best. Furthermore, we find that ~0.5% of our LBGs from z~3 to z~6 are detected individually in the X-ray band. These LBGs have spectral shapes and luminosities characteristic of moderate-power AGNs (e.g., Seyfert galaxies and quasars).


Lead the scientific data analyses and conclusions and wrote resulting publication.