CONICET | Buscador de Institutos y Recursos Humanos

The current paradigm assumes that galaxies form by baryon condensation within the potential wells defined by the collisionless collapse of dark matter halos, but the diversity of astrophysical mechanisms involved in galaxy formation does not allow us to determine how galaxies occupy halos. In this context, the HOD describes the probability distributionthat a virialized halo of mass $M_{h}$ contains $N$ galaxies with somespecified characteristic, for example, in a certain range of absolute magnitude.In this work, we implement the background subtraction technique proposed and evaluated in cite{rodriguez15} both in a galaxy survey as in a mock catalogue.Our method statistically estimates the number of galaxies that are in front of and/or behind the group (hereafter background galaxies), but, in projection, seem to belong to it and allows us to discount these objects. In this way, we can combine two catalogues that share the same sky area, one of groups and another of galaxies. For each group the method requires mass, redshift, angular positions and a characteristic radius, whereas for galaxies only angular positions and apparent magnitudes will be necessary.To estimate the HOD, we compute the absolute magnitude of galaxies assuming that all galaxies are located at the same redshift of the group $z_{gr}$:M=m-25-5log (d_L(z_{gr}))where $d_L(z_{gr})$ is the luminosity distance in Mpc at $z_{gr}$. We determine, statistically the background contribution and discount it from the group. We do this for different absolute magnitudes limits thus, if $M_{lim}$ sets the upper limit for the range of absolute magnitudes where the HOD will be estimated, we choose those galaxies that meet $Mleq M_{lim}$.With this procedure we can estimate the number of galaxies ($N$) that each group has and then, binning groups in mass intervals, obtain the HOD as the average of $N$, ($$).