Intergalactic Transmission and its Impact on the Ly{\alpha} Line

We study the intergalactic transmission of radiation in the vicinity of the Ly{\alpha} wavelength. Simulating sightlines through the intergalactic medium (IGM) in detailed cosmological hydrosimulations, the impact of the IGM on the shape of the line profile from Ly{\alpha} emitting galaxies at redshifts 2.5 to 6.5 is investigated. In particular we show that taking into account the correlation of the density and velocity fields of the IGM with the galaxies, the blue part of the spectrum may be appreciably reduced, even at relatively low redshifts. This may in some cases provide an alternative to the often-invoked outflow scenario, although it is concluded that this model is still a plausible explanation of the many asymmetric Ly{\alpha} profiles observed. Applying the calculated wavelength dependent transmission to simulated spectra from Ly{\alpha} emitting galaxies, we derive the fraction of photons that are lost in the IGM, in addition to what is absorbed internally in the galaxies due to dust. Moreover, by comparing the calculated transmission of radiation blueward of the Ly{\alpha} line, the total optical depth to Thomson scattering of cosmic microwave background, with corresponding observations, we are able to constrain the epoch when the Universe was reionized to z <~ 8.5.Comment: Substantially extended, ~30 references added, 1.5 page extra (article style) in particular on the impact of the IGM at z~5.8 and z~6.5, 2 extra figures, unnecessary fluff cut out, accepted for publication in Ap

Lyman alpha Resonant Scattering in Young Galaxies - Predictions from Cosmological Simulations

We present results obtained with a 3D, Ly alpha radiative transfer code, applied to a fully cosmological galaxy formation simulation. The developed Monte Carlo code is capable of treating an arbitrary distribution of source Ly alpha emission, neutral hydrogen density, temperature, and peculiar velocity of the interstellar medium. We investigate the influence of resonant scattering on the appearance and properties of young galaxies by applying the code to a simulated "Lyman Break Galaxy" at redshift z = 3.6, and of star formation rate 22 M_sun/yr and total Ly alpha luminosity 2.0 X 10^43 erg/s. It is found that resonant scattering of Ly alpha radiation can explain that young galaxies frequently are observed to be more extended on the sky in Ly alpha than in the optical. Moreover, it is shown that, for the system investigated, due to the anisotropic escape of the photons, the appearent maximum surface brightness can differ by a factor of ~15, and the total derived luminosity by a factor of ~4, depending on the orientation of the system relative to the observer.Comment: Letter updated to match version published in Ap