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We present a new model of the extragalactic background light (EBL) andcorresponding gamma-gamma opacity for intergalactic gamma-ray absorption from z= 0 up to z = 10, based on a semi-analytical model of hierarchical galaxyformation that reproduces key observed properties of galaxies at variousredshifts. Including the potential contribution from Population III stars andfollowing the cosmic reionization history in a simplified way, the model isalso broadly consistent with available data concerning reionization,particularly the Thomson scattering optical depth constraints from WMAP. Incomparison with previous EBL studies up to z ~ 3-5, our predicted gamma-gammaopacity is in general agreement for observed gamma-ray energy below 400/(1 + z)GeV, whereas it is a factor of ~ 2 lower above this energy because of acorrespondingly lower cosmic star formation rate, even though the observed UVluminosity is well reproduced by virtue of our improved treatment of dustobscuration and direct estimation of star formation rate. The horizon energy atwhich the gamma-ray opacity is unity does not evolve strongly beyond z ~ 4 andapproaches ~ 20 GeV. The contribution of Population III stars is a minorfraction of the EBL at z = 0, and is also difficult to distinguish throughgamma-ray absorption in high-z objects, even at the highest levels allowed bythe WMAP constraints. Nevertheless, the attenuation due to Population II starsshould be observable in high-z gamma-ray sources by telescopes such as Fermi orCTA and provide a valuable probe of the evolving EBL in the rest-frame UV. Thedetailed results of our model are publicly available in numerical form at theURL http://www.slac.stanford.edu/~yinoue/Download.html.

Extragalactic Background Light from Hierarchical Galaxy Formation: Gamma-ray Attenuation up to the Epoch of Cosmic Reionization and the First Stars