• Adelberger, Kurt L.
• Pettini, Max
• Steidel, Charles C.

Abstract

We report the detection of significant Lyman-continuum flux in the composite spectrum of 29 Lyman-break galaxies (LBGs) with redshifts &lt;z&gt;=3.40+/-0.09. After correction for opacity due to intervening absorption using a new composite QSO spectrum evaluated at the same redshift, the ratio of emergent flux density at 1500 Å in the rest frame to that in the Lyman continuum is L(1500 )/L(900 )=4.6+/-1.0. If the relative intensity of the inferred escaping Lyman-continuum radiation is typical of LBGs at z~3 (the galaxies in this sample are drawn from the bluest quartile of LBG spectral energy distributions due to known selection effects), then observed LBGs produce about 5 times more H-ionizing photons per unit comoving volume than QSOs at z~3. The associated contribution to the metagalactic ionizing radiation field is J<SUB>ν</SUB>(912 Å)~1.2+/-0.3×10<SUP>-21</SUP> ergs s<SUP>-1</SUP> cm<SUP>-2</SUP> Hz<SUP>-1</SUP> sr<SUP>-1</SUP> at z~3, very close to most estimates of the radiation field background based on the ``proximity effect.'' A preliminary analysis of the density of faint QSOs in our Lyman-break galaxy survey indicates that the standard extrapolated QSO luminosity function may slightly overpredict the QSO contribution to J<SUB>ν</SUB>(912 ) at z~3. We briefly discuss the implications of a galaxy-dominated UV background at high redshifts. Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation....

Topics

• density
• impedance spectroscopy
• composite