We have studied the effects of gas density inhomogeneities on the escape of ionizing Lyman continuum (Lyc) photons from Milky Way type galaxies via 3D numerical simulations using the Monte Carlo radiative transfer code CRASH. To this aim a comparison between a smooth Gaussian distribution (GDD) and an inhomogeneous, fractal one (FDD) has been made with realistic assumptions for the ionizing stellar sources based on available data in the solar neighbourhood. In both cases the escape fraction fesc increases with ionization rate 𝒩˙? (although for the FDD with a flatter slope) and they become equal at 𝒩˙?=2×1050s-1 where fesc=0.11. FDD allows escape fractions of the same order also at lower 𝒩˙?, when Lyc photon escape is sharply suppressed by GDD. Values of the escape fraction as high as 0.6 can be reached (GDD) for 𝒩˙?~9×1050s-1, corresponding to a star formation rate (SFR) of roughly 2Msolaryr-1 at this ionizing luminosity the FDD is less transparent (fesc~0.28). If high-redshift galaxies have gas column densities similar to local ones, and are characterized by such high SFRs and by a predominantly smooth (i.e. turbulence-free) interstellar medium, our results suggest that they should considerably contribute to - and possibly dominate - the cosmic UV background.
Lyman Continuum Escape from Inhomogeneous ISM
2002
Abstract
We have studied the effects of gas density inhomogeneities on the escape of ionizing Lyman continuum (Lyc) photons from Milky Way type galaxies via 3D numerical simulations using the Monte Carlo radiative transfer code CRASH. To this aim a comparison between a smooth Gaussian distribution (GDD) and an inhomogeneous, fractal one (FDD) has been made with realistic assumptions for the ionizing stellar sources based on available data in the solar neighbourhood. In both cases the escape fraction fesc increases with ionization rate 𝒩˙? (although for the FDD with a flatter slope) and they become equal at 𝒩˙?=2×1050s-1 where fesc=0.11. FDD allows escape fractions of the same order also at lower 𝒩˙?, when Lyc photon escape is sharply suppressed by GDD. Values of the escape fraction as high as 0.6 can be reached (GDD) for 𝒩˙?~9×1050s-1, corresponding to a star formation rate (SFR) of roughly 2Msolaryr-1 at this ionizing luminosity the FDD is less transparent (fesc~0.28). If high-redshift galaxies have gas column densities similar to local ones, and are characterized by such high SFRs and by a predominantly smooth (i.e. turbulence-free) interstellar medium, our results suggest that they should considerably contribute to - and possibly dominate - the cosmic UV background.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
