Prof. David Alonso

Abstract:

In this paper, we present a new method to extract cosmological parameters using the radial scale of the baryon acoustic oscillations as a standard ruler in deep galaxy surveys. The method consists of an empirical parametrization of the radial two-point correlation function, which provides a robust and precise extraction of the sound horizon scale at the baryon drag epoch. Moreover, it uses data from galaxy surveys in a manner that is fully cosmology independent and therefore unbiased. A study of the main systematic errors and the validation of the method in cosmological simulations are also presented, showing that the measurement is limited only by cosmic variance. We then study the full information contained in the baryon acoustic oscillations, obtaining that the combination of the radial and angular determinations of this scale is a very sensitive probe of cosmological parameters, able to set strong constraints on the dark energy properties, even without combining it with any other probe. We compare the results obtained using this method with those from more traditional approaches, showing that the sensitivity to the cosmological parameters is of the same order, while the measurements use only observable quantities and are fully cosmology independent.

Abstract:

We study the non-linear gravitational collapse of dark matter into halos through numerical N-body simulations of Lemaître–Tolman–Bondi void models. We extend the halo mass function formalism to these models in a consistent way. This extension not only compares well with the simulated data at all times and radii, but it also gives interesting clues about the impact of the background shear on the growth of perturbations. Our results give hints about the possibility of constraining the background shear via cluster number counts, which could then give rise to strong constraints on general inhomogeneous models, of any scale.

Abstract:

We propose a new method for the extraction cosmological parameters using the baryon acoustic oscillation (BAO) scale as a standard ruler in deep galaxy surveys with photometric determination of redshifts. The method consists in a simple empirical parametric fit to the angular two-point correlation function ω(θ). It is parametrized as a power law to describe the continuum and as a Gaussian to describe the BAO bump. The location of the Gaussian is used as the basis for the measurement of the sound horizon scale. This method, although simple, actually provides a robust estimation, since the inclusion of the power law and the use of the Gaussian remove the shifts which affect the local maximum. We discuss the effects of projection bias, non-linearities, redshift space distortions and photo-z precision and apply our method to a mock catalogue of the Dark Energy Survey, built upon a large N-body simulation provided by the MICE collaboration. We discuss the main systematic errors associated with our method and show that they are dominated by the photo-z uncertainty.