Multi probe cosmological analysis with the dark energy survey
Ongoing and future photometric surveys will enable detailed measurements of the late time Universe and powerful tests of the nature of dark energy and General Relativity. These surveys will be able to obtain cosmological constraints from multiple probes, and the combination of these probes can improve their robustness and constraining power. This thesis is focused on the combination of multiple tracers of large scale structure (LSS) to obtain tighter cosmological constraints. First, we combine the galaxy clustering from the Dark Energy Survey (DES) Year 1 (Y1) data with CMB lensing from the optimal combination of South Pole Telescope (SPT) and Planck, obtaining constraints on the galaxy bias, the growth function and the cosmological parameters. Our results are consistent with LCDM and other measurements of DES Y1. However, their constraining power is limited due to conservative scale cuts. We expect an improved signal to noise in future analyses. We then combine the galaxy clustering of two different galaxy samples (the so called multi tracer approach) to explore the constraints on redshift space distortions (RSD) and primordial non Gaussianities (PNG) For this purpose, we consider a pair of optimistic samples (with large bias differences and number densities) and the DES Year 3 (Y3) lens samples. We find that the constraints on RSD can be improved a factor of five at low redshift with respect to a single tracer, and the constraints on PNG can be improved more than a factor three. We also test the impact of including CMB lensing cross correlations in our analysis, in which we keep the cosmology fixed, finding it mainly improves the galaxy bias constraints. Last, we define and optimize a magnitude limited galaxy sample to be used for the galaxy clustering measurements in the DES Y3 analysis, in combination with galaxy galaxy lensing. We rely on Fisher forecasts, and we test how these change given the variations obtained for the number density and estimated redshift uncertainty for a set of magnitude cuts. We also characterize the impact of redshift binning choices in our cosmological constraints for this sample and the other DES Y3 lens sample: redmagic. Finally, our forecasts show that we can potentially obtain 15\ tighter constraints with this magnitude limited sample, compared to redmagic.