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Pierleoni, Marco (2010): CRASHa coupling continuum and line radiative transfer. Dissertation, LMU München: Fakultät für Physik
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The detection of lya lines from local and distant objects has always been of great importance in astrophysics. It has been extensively used as indicator of redshift, as a measurement of the star formation activity of galaxies and as a probe of their internal structure. In the last few years an increasing interest has been devoted to the search of lya emitters (LAEs) at high redshift, which are expected to be characterized by a strong lya emission, but significantly attenuated by dust absorption. Emission of lya photons from high redshift sources has also an impact on the detectability of 21~cm line from neutral hydrogen in the Intergalactic Medium (IGM). This work is focused on the study, analysis and implementation of a new radiative transfer scheme (CRLya) which, for the first time in the literature, follows simultaneously the propagation of lya and ionizing radiation self-consistently. This allows to investigate the effects of evolving ionization configurations on the propagation of lya radiation and on the shaping of the line emerging from single objects. The implementation introduces the time evolution for lya photons (a feature commonly neglected in line radiative transfer codes) and, to reduce the computational time needed to follow each scattering, adopts a statistical approach to the lya treatment by making extensive use of pre-compiled tables. I find that the emerging spectra keep memory of the ionization history which generates a given ionization configuration of the gas and, to properly account for this effect, a self-consistent joint evolution of line and ionizing continuum radiation as implemented in CRLya is necessary. As next step, I implemented new features in CRLya: a new emission system, diffuse lya photons from recombination and treatment of dust. With a new test performed on a simulated galaxy at redshift z~10, I show the ability of the code to determine the variations of the lya radiation field while the gas in which it propagates is affected by the ionizing radiation emitted by the stars within the galaxy. In this test, the lya radiation is generated by both stars and recombining ionized gas. Finally I tackle the impact of lya photon scattering on the IGM temperature. This is an important issue since lya photons could be able to heat the IGM temperature above the CMB temperature and render the 21 cm line visible in emission. In the last Chapter, I discuss the implementation of the lya heating in \CRLya and I analyze how the temperature is modified by changing the most relevant physical parameters in the simulation.