Beamed Ly<i>α</i>emission through outflow-driven cavities

Abstract

We investigate the radiative transfer of Lyman alpha photons through\nsimplified anisotropic gas distributions, which represent physically motivated\nextensions of the popular 'shell-models'. Our study is motivated by the notion\nthat (i) shell models do not always reproduce observed Lyman alpha spectral\nline profiles, (ii) (typical) shell models do not allow for the escape of\nionizing photons, and (iii) the observation &amp; expectation that winds are more\ncomplex, anisotropic phenomena. We examine the influence of inclination on the\nLyman alpha spectra, relative fluxes and escape fractions. We find the flux to\nbe enhanced/suppressed by factors up to a few depending on the parameter range\nof the models, corresponding to a boost in equivalent width of the same\namplitude if we neglect dust. In general, lower mean optical depths tend to\nreduce the impact of anisotropies as is expected. We find a correlation between\nan observed peak in the -- occasionally triple-peaked -- spectrum at the\nsystemic velocity and the existence of a low optical depth cavity along the\nline of sight. This can be of importance in the search for ionizing photons\nleaking from high- redshift galaxies since these photons will also be able to\nescape through the cavity.\n