Galaxy voids as cosmological laboratories
Final Report Abstract
This DFG research project was based on the exploration of two complementary avenues for the use of cosmic voids as cosmological laboratories: the analysis of the void density profiles and the void number density. With regard to the void density profiles, we developed a new cosmological test based on a physical model for the void-galaxy cross-correlation function projected along and perpendicular to the line of sight. We treat correlations in terms of void-centric angular distances and redshift differences between void-galaxy pairs, hence it is not necessary to assume a fiducial cosmology. This model reproduces the coupled dynamical (RSD) and geometrical (AP) distortions that affect the correlation measurements. It also takes into account the scale mixing due to the projection ranges in both directions. The model is general, so it can be applied to an arbitrary cylindrical binning scheme, not only in the case of the projected correlations. It primarily depends on two cosmological parameters: Ωm , the matter fraction of the Universe today (sensitive to GD), and β, the ratio between the growth rate factor of density perturbations and the tracer bias (sensitive to RSD). In the context of the new generation of galaxy spectroscopic surveys, we calibrated the test using the Millennium XXL simulation for different redshifts. The method successfully recovers the cosmological parameters. We studied the effect of measuring with different projection ranges, finding robust results up to wide ranges. The resulting data covariance matrices are relatively small, which reduces the noise in the Gaussian likelihood analysis and will allow the usage of a smaller number of mock catalogues. The performance evaluated in this work indicates that the developed method is a promising test to be applied on real data. However, it is worth mentioning that this method is a non-fiducial test given a galaxy spectroscopic catalogue and a set of underdense centres. The void identification is a difficult task that deserves particular attention before applying the test to observational data. A non-fiducial way of finding voids has still to be found and the non-trivial effects of identification in Mpc-scales must be completely understood, a topic that we are now addressing. With regard to the void number density, we improved our spherical void finding method, so that voids provided by this void finder are ready to be compared with theory, with no necessity of a further post-processing cleaning steps. For our tests, we used the Minerva cosmological simulations. we studied different cosmology dependent void abundance models. They work satisfactorily with voids identified on the matter distribution. The modelling of the complex effect of galaxy bias in order to constrain cosmology using galaxy voids identified on real data from the spectroscopic surveys. Finally, we studied the effects of GD and RSD, finding successful void volume correction to account for the former, and we are acrively working on the modeling of the latter. The final model will be applied to a new catalogue of cosmic voids identified in the final galaxy samples of BOSS.
Publications
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Non-fiducial cosmological test from geometrical and dynamical distortions around voids. Monthly Notices of the Royal Astronomical Society, 019
Carlos M. Correa, Dante J. Paz, Nelson D. Padilla, Andrés N. Ruiz, Raul Angulo, and Ariel G. Sánchez
