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Accurate knowledge of the morphology of halos and its evolution are key constraints on the galaxy formation model as well as a determinant parameter of the strong-lensing phenomenon. Using the cosmological hydrodynamic simulation, the Evolution and Assembly of GaLaxies and their Environments (EAGLE), we aim to provide a comprehensive analysis of the evolution of the morphology of galaxy halos and of their mass distributions with a focus on the snapshot at redshift z=0. 5. We developed an iterative strategy involving a principal component analysis (PCA) to investigate the properties of the EAGLE halos and the differences in alignment between the various components. The mass distributions of the dark-matter (DM), gas, and star halos are characterised by a half-mass radius, a concentration parameter and (projected) axis ratios. We present statistics of the shape parameters of 336\, 540 halos from the EAGLE RefL0025N0376 simulation and describe their evolution from redshift z=15 to z=0. We measured the three-dimensional and two-dimensional projected shape parameters for the DM, the gas, and the star components as well as for all particles. At z=0. 5, the minor axis of gas aligns with the minor axis of DM for massive halos (M>10^12 M_), but this alignment is poorer for less massive halos. The DM halos axis ratios b/a and c/a have median values of 0. 82 0. 11 and 0. 64 0. 12, respectively. The sphericity of gas in halos w/ and w/o stars appears to be negatively correlated to the total mass, while the sphericity of DM is insensitive to it. The measured projected axis ratios, bₚ/aₚ, of star halos at z=0. 5 have a median value of 0. 80 0. 07, which is in good agreement with ground-based and space-based measurements within 1. For DM halos, we measure a value of 0. 85 0. 06.
Petit et al. (Sat,) studied this question.