Halo occupation distribution in galaxy surveys

FACUNDO RODRIGUEZ

Córdoba

Encuentro; 8° Friend of Friend Meeting; 2018

Instituto de Astronomía Teórica y Experimental

The present work is framed within the studies of the large-scale structure of theUniverse and, in particular, in the relationship between ordinary (or baryonic) matterand the so-called ?dark matter?. To contextualize our studies, we decided to start witha historical review about the researches and controversies that occurred in the area inwhich this thesis is performed.The current paradigm assumes that galaxies are formed inside the halos of dark matter.However, a great diversity of astrophysical mechanisms are involved in the formationprocess, which makes it difficult to determine how many galaxies populate a halo of agiven mass. In order to estimate the relationship between galaxies and halos, differentstatistical estimatorsemerged that allow linking the mass of the halos with the numberof galaxies they possess. One of them, which was established as a simple and at the sametime powerful tool, is the halo occupation distribution (known in Spanish as DOH), thecentral concept of the present work. This estimator is defined as the probability that ahalo of mass M contains N galaxies with some characteristics, giving the possibility ofassociating, in a statistical way, galaxies and haloes.At present, large catalogues of galaxies are available that allow us to identify groupsof galaxies, determine their mass and then study the DOH. But, for this, only the spec-troscopic information provided by the surveys is used, without taking advantage of largeamounts of photometric data that are also released by them. That is why, one of theobjectives of this work was to propose a method of discounting background galaxies thatallows combining photometric and spectroscopic data to expand the range of luminositiesand masses in which DOH can be studied. To evaluate this technique we employed anotherof the most used tools in the studies of the large-scale structure of the universe: syntheticcatalogues. From simulations of dark matter populated with semi-analytical models wemade synthetic catalogues that allowed us to establish the virtues and shortcomings ofour technique before implementing it in the Sloan Digital Sky Survey (SDSS) catalogue.Another of the objectives that we proposed in this thesis was to compare the DOH withother estimators. In particular, we compared it with the mass-richness relation obtainedfrom gravitational lens studies. For this we worked with other researchers, who measuredthe mass and richness of a sample of groups and we, using the technique mentioned in theprevious paragraph, determined the DOH of said sample. But, since both estimators arenot directly comparable, we use the same determinations but we modify the calculationof the DOH to be able to make the comparison. We obtained a great agreement betweenboth estimates.