Escape of Lyα and continuum photons from star-forming galaxies

Abstract

A large number of high-redshift galaxies have been discovered via their narrow-band Lya line or broad-band continuum colours in recent years. The nature of the escaping process of photons from these early galaxies is crucial to understand galaxy evolution and the cosmic reionization. Here, we investigate the escape of Lya, non-ionizing UV-continuum (λ lt; 1300-1600Å in rest frame), and ionizing photons (λ <912 Å) from galaxies by combining a cosmological hydrodynamic simulation with three-dimensional multiwavelength radiative transfer calculations. The galaxies are simulated in a box of 53 h-3 Mpc3 with high resolutions using the Aquila initial condition which reproduces a MilkyWay-like galaxy at redshift z = 0.We find that the escape fraction (fesc) of these different photons shows a complex dependence on redshift and galaxy properties: fLyαesc and fUVesc appear to evolve with redshift, and they show similar, weak correlations with galaxy properties such as mass, star formation, metallicity, and dust content, while fIonesc remains roughly constant at ̃0.2 from z ̃ 0 to 10, and it does not show clear dependence on galaxy properties. fLyαesc correlates more strongly with f UV esc than with f Ion esc . In addition, we find a relation between the emergent Lya luminosity and the ionizing photon emissivity of Lyman Alpha Emitters (LAEs). By combining this relation with the observed luminosity functions of LAEs at different redshift, we estimate the contribution from LAEs to the reionization of intergalactic medium (IGM). Our result suggests that ionizing photons from LAEs alone are not sufficient to ionize IGM at z ≥ 6, but they can maintain the ionization of IGM at z ̃ 0-5. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.