Determination of Halo Occupation Distribution

In this work, we propose a new method to calculate the Halo Occupation Distribution (HOD). It consist of subtract galaxies that are in front or behind the group (background galaxies), but, for projection effects, seem to belong to this. This allows to combine spectroscopic information from catalogs of galaxy groups with photometric information from catalogs of galaxies, the main advantage of this is the possibility to estimate the HOD in more ranges of absolute magnitudes. To evaluate the procedure, we used mock catalogs of galaxies and groups constructed with an imposed HOD. We compare this fiducial HOD with the obtained results by applying our method. Finally, we implement background subtraction in the Sloan Digital Sky Survey DR7, compare to the results of Yang et al. (2008) and calculate the HOD in other ranges of absolute magnitudes.