AVISM: Algorithm for Void Identification in coSMology

Abstract: Cosmic voids are key elements in our understanding of the large-scale structure of the Universe. They are crucial to constrain cosmological parameters, understand the structure formation and evolution of our Universe, and they could also be pristine laboratories for studying galaxy formation without all the hassle due to environmental effects. Thus, the ability to accurately and consistently identify voids, both in numerical simulations and in observations, becomes mandatory. We present Algorithm for Void Identification in coSMology (AVISM), a new void finder for analysing both cosmological simulation outputs and observational galaxy catalogues. In the first case, the code should handle raw particle or cell data, dark matter halos or synthetic galaxy catalogues. In the case of observational data, the code should be coupled with external tools providing with the required dynamical information to apply the algorithm. A set of numerical tests designed to assess the code's capabilities are carried out. AVISM's performance is also compared, both statistically and on a one-to-one basis, with the DIVE and ZOBOV state-of-the-art void finders using as input a dark matter halo catalogue from a large-volume cosmological simulation. An application to a galaxy survey is provided to demonstrate the code's ability to handle real data. We have designed a new void finder algorithm that combines geometrical and dynamical information to identify void regions plus a hierarchical merging process to reconstruct the whole 3D structure of the void. The outcome of this process is a void catalogue with complex boundaries without assuming a prior shape. This process can be repeated at different levels of resolution using finer grids, leading to a list of voids-in-voids and a proper description of void substructure.