Intrinsic Alignments of Galaxies with The EFT Model

Abstract

The focus of this thesis is to study Intrinsic Alignments (IA) of galaxies using the Effective Field Theory (EFT) model. The EFT model is perturbative, and in this work it is explored at the one-loop level. There are several other IA models such as: Linear Alignment (LA), Non-Linear Alignment (NLA), and the Halo model etc. The results focus on a comparison between the EFT and the NLA model. The EFT model relies on a perturbative expansion of local operators, and it can be applied to the local dark matter (DM) density field and the intrinsic shape of galaxies.

The contribution due to the higher derivatives of the tidal field to the 3D IA power spectrum has a bias parameter associated with the intrinsic shape denoted as b^{g}_{R}. This motivates the following research question: how does the bias parameter b^{g}_{R} of the EFT model affect constraints on cosmological parameters relative to the NLA model ? Assuming that the “true” Universe follows the NLA model. The bias vector formalism allows for quantifying the bias that is input into the modelling due to systematic signals by using the Fisher matrix, and the formalism used here is based on the work by Amara et al. (2008). The choices for the analysis conducted are suited towards the next generation Stage IV surveys like LSST.

The primary b^{g}_{R}= -0.02 value is changed to increasingly negative values to observe the effect in the bias vector ellipse (which is mis-modelled as EFT) relative to the fiducial ellipse that corresponds the NLA model at a confidence level of 68.3% (1σ) and 95.4% (2σ) for two cosmological parameter spaces, namely (Ωm, σ8) and (w0,wa). This shows clear trends in the bias vector ellipse with a shift towards (high Ωm, low σ8) and (high w0, low wa) for both of the parameter spaces considered, relative to the fiducial (NLA) ellipse. The results suggest a significant bias in constraints relative to the fiducial (NLA) values used for the cosmology if the b^{g}_{R} value is changed to increasingly negative values at or greater than b^{g}_{R}=-0.08, based on the range of b^{g}_{R} values considered here.