Contribution of galaxies to the background hydrogen-ionizing flux |
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Authors: | Julien E G Devriendt Shiv K Sethi Bruno Guiderdoni & Biman B Nath |
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Institution: | Institut d'Astrophysique de Paris, CNRS, 98bis Boulevard Arago, F-75014 Paris, France,;Raman Research Institute, Bangalore-560080, India |
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Abstract: | We estimate the evolution of the contribution of galaxies to the cosmic background flux at 912 ? by means of a semi-analytic model of galaxy formation and evolution. Such modelling has been quite successful in reproducing the optical properties of galaxies. We assume that high-redshift damped Lyman α systems are the progenitors of present-day galaxies, and we design a series of models that are consistent with the evolution of cosmic comoving emissivities in the available near-infrared, optical, ultraviolet and far-infrared bands along with the evolution of the neutral hydrogen content and average metallicity of damped Lyman α systems. We use these models to compute the galactic contribution to the Lyman-limit emissivity and background flux for 0 ? z ≤ 4. We take into account the absorption of Lyman-limit photons by H I and dust in the interstellar medium of the galaxies. We find that the background Lyman-limit flux due to galaxies might dominate (or be comparable to) the contribution from quasars at almost all redshifts if the absorption by H I in the interstellar medium is neglected. Such H I absorption would result in a severe diminishing of this flux — by almost three orders of magnitude at high redshifts and by one to two orders at z ? 0. Though the resulting galaxy flux is completely negligible at high redshifts, it is comparable to the quasar flux at z ? 0. |
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Keywords: | methods: analytical dust extinction galaxies: evolution galaxies: fundamental parameters cosmology: theory |
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