Speaker
Description
Galaxies that are spatially correlated, also show position-shape correlations of their major axes. This correlation, called intrinsic alignment, is a major contaminant in cosmological analyses of weak lensing surveys and therefore needs to be modelled well and understood. While intrinsic alignment correlations have been established and modelled quite well for linear scales for large central (red) ellipticals, the exact connection to further galaxy evolution and properties remains unclear. One such unknown, is the alignment of disk galaxies for which hydrodynamical simulations give controversial predictions. Another area where many questions remain is that of the redshift evolution of intrinsic alignments and how baryonic processes and galaxy evolution, e.g. gas inflows or mergers, influence them. Both morphology and kinematics are thought to be strongly correlated with intrinsic alignment. As hydrodynamical simulations become more realistic, we can uncover exactly which galaxy evolution processes and properties influence intrinsic alignments, what drives these alignments; learning more about how galaxies are oriented within their halos and towards the large scale structure.
I have performed a direct comparison of TNG300-1, Horizon-AGN and EAGLE, remeasuring variables for consistency, which are publicly available. This comparison reveals that while the simulations agree on many main trends, there are also substantial differences between them. In all three simulations, galaxies show radial alignments that are higher for red or dispersion dominated galaxies. However, the simulations vary in correlation amplitude and in the impact of choosing samples based on colour or kinematics. Furthermore, when comparing the redshift evolution of galaxy and halo alignments between TNG300 and COLIBRE, their halo alignments agree well, with TNG galaxies evolving similarly, but COLIBRE galaxies do not show significant evolution in redshift. The inclusion of cold gas in COLIBRE possibly leads to substantially different shapes and orientation evolution of galaxies than in TNG300. This difference in redshift evolution is measured for the full samples ($M_\star>10^{9.27} \mathrm{M}_\odot/h$) as well as sub-populations split by colour, mass or kinematic properties. Finally, I will also present how combing multiple projections of shapes leads to gain in signal-to-noise in both measurements and modelling. This research gives insight on the impact of galaxy properties and evolution on intrinsic alignments and also leads to better priors that can be used to mitigate the intrinsic alignments effects on weak lensing analyses.
| Other topic / keywords: | Galaxy evolution |
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