Astrocladistics: A Phylogenetic Analysis of Galaxy Evolution II. Formation and Diversification of Galaxies |
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Authors: | Didier Fraix-Burnet Philippe Choler Emmanuel JP Douzery Anne Verhamme |
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Institution: | (1) Laboratoire d’Astrophysique de Grenoble, Grenoble, France;(2) Laboratoire d’ Ecologie Alpine, Grenoble, France;(3) Laboratoire de Paleontologie, Phylogenie et Paleobiologie, Institut des Sciences de l’ Evolution de Montpellier, Montpellier, France |
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Abstract: | This series of papers is intended to evaluate astrocladistics in reconstructing phylogenies of galaxies. The objective of
this second paper is to formalize the concept of galaxy formation and to identify the processes of diversification. We show
that galaxy diversity can be expected to organize itself in a hierarchy. In order to better understand the role of mergers,
we have selected a sample of 43 galaxies from the GALICS database built from simulations with a hybrid model for galaxy formation
studies. These simulated galaxies, described by 119 characters and considered as representing still undefined classes, have
experienced different numbers of merger events during evolution. Our cladistic analysis yields a robust tree that proves the
existence of a hierarchy. Mergers, like interactions (not taken into account in the GALICS simulations), are probably a strong
driver for galaxy diversification. Our result shows that mergers participate in a branching type of evolution, but do not
seem to play the role of an evolutionary clock. |
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