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Toward a new level of modeling of environmental effects on galaxies

Abstract : Galaxies lie in a large panel of environments from isolated galaxies, to pairs, groups or clusters. The environment is expected to have an impact on galaxy properties such as morphology, stellar formation, metallicity\ldots. Some studies already tried to quantify the importance of the global environment (linked to the dark matter halo mass) and the local environment (galaxy position in the group). These studies have shown that the environment plays a minor role except for low mass galaxies. But the quantification of the environment is difficult since detected groups in redshift space (the only one accessible by the observer) are very elongated, making it difficult to extract spherical groups in real space. If these quantification errors are too important, environment effects will not be measured correctly. Moreover, other physical processes are at work inside groups whose relative roles are not well understood. For example, major or minor mergers (rich or poor in gas, between satellite galaxies, or after the decay of the orbit of a satellite onto the central galaxy by dynamical friction), rapid flybys harassing galaxies, stripping of the interstellar gas by ram pressure or of the gaseous reservoir by tidal forces. Although semi-analytical codes of galaxy formation from initial conditions of a LambdaCDM Universe fit well a large set of observed relations, there are still some discrepancies that might be possibly explained by a lack of correct physical recipes of environmental effects in these models. Our goal with this thesis is to have a detailed comprehension of the role of environment on galaxy properties, and finally determine the major physical processes in the modulation of these properties with both local and global environment. For this, an optimal extraction of galaxy groups from the projected phase space is necessary. We performed a study and re-implementation of some existing group finder to estimate their strengths and weaknesses in the detection of galaxy groups. A galaxy mock catalogue in redshift space, designed to mimic the primary spectroscopic sample of the SDSS survey was created to apply several galaxy group algorithms. An advantage is the already known membership that we can compare to galaxy groups extracted from redshift space. Semi-analytical codes of galaxy formation give us such galaxy catalogs we transformed to be coherent with the vision of an observer. With these mock catalogues, we tested the very popular Friends-of-Friends grouping algorithm. We determined the optimal linking lengths against the set of tests and optimal criterion we developed to judge the efficiency of an algorithm. It appears that this choice of linking lengths depends on the scientific goal to do with the group catalogue. A large part of the thesis consisted on the realization of a new grouping algorithm called MAGGIE (Models and Algorithm for Galaxy Groups, Interlopers and Environment), Bayesian and probabilistic. MAGGIE uses our priors acquired with analysis of cosmological simulations for large scale structure and of observations obtained from large galaxy surveys, to better constrain the selection of galaxy groups from redshift space. Comparison of MAGGIE with the FoF algorithm shows that MAGGIE is superior in avoiding the fragmentation of real space groups, the membership selection (completeness, reliability) and in the group properties (group mass, luminosity). The better performance of MAGGIE comes from its probabilistic nature, the use of astrophysical and cosmological priors, and the use of halo abundance matching technique linking central galaxy distributions (stellar mass or luminosity) to physical properties of dark matter halos. The future application of MAGGIE on galaxy surveys such as the Sloan Digital Sky Survey or the deeper Galaxy and Mass Assembly, taking care of their own observational problems, should improve our understanding of the modulation of galaxy properties with their global and local environments and physical processes operating inside galaxy groups.
Keywords : astronomy
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  • HAL Id : tel-02095295, version 1

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Manuel Duarte. Toward a new level of modeling of environmental effects on galaxies. Astrophysics [astro-ph]. Observatoire de Paris, 2014. English. ⟨tel-02095295⟩

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