<p>Validerat; 20101217 (root)</p>

Inici de l’estudi de l’efecte de les col•lisions entre ions i neutres en l’esmorteïment d’ones magnetohidrodinàmiques. Es considera un plasma parcialment ionitzat, infinit i homogeni, i s’analitza l’esmorteïment temporal i espacial de les ones magnetoacústiques i les ones d’Alfvén tan en el cas de plasmes adiabàtics com en el de no adiabàtics. Mentre l’esmorteïment temporal de les ones MHD en plasmes adiabàtics parcialment ionitzats és degut a les col•lisions entre ions i neutres, en el cas no adiabàtic és possible estudiar la importància de cada mecanisme d’esmorteïment involucrat. Per altre banda, en el cas de l’esmorteïment espacial s‘han estudiat també ones MHD adiabàtiques i no adiabàtiques en plasmes resistius totalment ionitzats així com en plasmes parcialment ionitzats, i hem inclòs la presència de fluxes. S’inicia l’estudi amb el desenvolupament de les equacions magnetohidrodinàmiques per un fluid considerant ionització parcial i s’aplica aquest conjunt d’equacions a diferents configuracions de plasmes. / The study of the effect of ion-neutral collisions on the damping of magnetohydrodynamic waves is started. We develop a set of one-fluid equations for a partially ionised plasma and use it in different plasma configurations. As a first step, the simplest plasma configuration is considered, an unbounded homogeneous partially ionised plasma. We study the temporal and spatial damping of magnetoacoustic and Alfvén waves in the case of adiabatic and non-adiabatic plasmas. While the time damping of MHD waves in adiabatic partially ionized plasmas is due to ion-neutral collisions, in the non-adiabatic case it is possible to study the importance of each of the different damping mechanisms involved. In the case of spatial damping we have considered adiabatic and non-adiabatic MHD waves in fully ionized resistive and partially ionised plasmas, and we have also included flows.

Lyman continuum (LyC) photons are known to be responsible for reionising the universe after the end of the Dark Ages, which marked a period called the Epoch of Reionisation (EoR). While these high-energy photons are thought to predominantly originate from young, hot, massive stars within the earliest galaxies, and contributions from high-energy sources like quasars and AGN, the origins of these photons are yet not well known and highly debated. Detecting LyC photons from the early galaxies near the EoR is not possible as they get completely absorbed by the intergalactic medium (IGM) on their way to us, which has prompted the development of various indirect diagnostics to study the amount of LyC photons contributed by such galaxies by studying their analogues at low redshifts. In this study, we probe the ionised interstellar medium (ISM) of seven Green Pea galaxies through spatially resolved[O III] λ5007/[O II] λ3727 (O32) and [O III] λ5007/Hα λ6562 (O3Hα) emission-line ratio maps, using data from the Multi Unit Spectroscopic Explorer (MUSE) onboard the Very large telescope (VLT). Out of the two ratios, the former has proven to be a successful diagnostic in predicting Lyman continuum emitters (LCEs). Along with the line ratio maps, the surface brightness profiles of the galaxies are also studied to examine the spatial distribution of the emission lines and the regions from which they originate. The resulting maps indicate whether the ISM of the galaxies is ionization-bounded or density-bounded. Our analysis reveals that a subset of the galaxies with ionization-bounded ISM exhibits pronounced ionisation channels in the outer regions. These channels are potential pathways through which Lyman continuum photons may escape. For density-bounded ISM, the ionised ISM extends well beyond the stellar regions into the halos of the galaxies, highlighting their potential contribution to the ionising photon budget during the EoR. The findings emphasise the importance of spatially resolved ISM studies in understanding the mechanisms facilitating the escape of LyC photons.