Euclid preparation

With about 1.5 billion galaxies expected to be observed, the very large number of objects in the Euclid photometric survey will allow for precise studies of galaxy clustering from a single survey, over a large range of redshifts, 0.2 < z < 2.5. In this work, we use photometric redshifts z ph to extract the baryon acoustic oscillation signal (BAO) from the Flagship galaxy mock catalogue with a tomographic approach to constrain the evolution of the Universe and infer its cosmological parameters. We measured the two-point angular correlation function in 13 redshift bins. A template-fitting approach was applied to the measurement to extract the shift of the BAO peak through the transverse Alcock–Paczynski parameter α . A joint analysis of all redshift bins was performed to constrain α at the effective redshift z eff = 0.77 with Markov chain Monte Carlo and profile likelihood techniques. We also extracted one α i parameter per redshift bin to quantify its evolution as a function of time. From these 13 α i , which are directly proportional to the ratio D A / r d , we constrain the product of the reduced Hubble constant and the sound horizon at the drag epoch, h r d , and the matter density parameter Ω m . From the joint analysis, we constrain D A / r d = 10.764 −0.084 +0.0839 at the 68% confidence level, which represents a three-fold improvement over current constraints from the Dark Energy Survey. As expected, the constraining power in the analysis of each redshift bin is lower, with an uncertainty ranging from ±1.23 to ±0.289. From these results, we constrain Ω m = 0.296 −0.059 +0.074 and h r d = 99.35 −4.55 +4.29 Mpc. We quantify the influence of analysis choices such as the template, scale cuts, and redshift bins, and systematic effects such as redshift-space distortions, over our constraints, both at the level of the extracted α i parameters and at the level of cosmological inference.

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