An improved method for the identification of galaxy systems: Measuring   the gravitational redshift by Dark Matter Haloes
  We introduce a new method for the identification of galaxy systems in redshift surveys based on the halo model. This method is a modified version of the K-means identification algorithm developed by Yang et al (2005). We have calibrated and tested our algorithms using mock catalogs generated using the Millennium simulations (Springel et al. 2005) and applied them to the NYU-DR7 galaxy catalog (based on the SDSS datasets). Using this local sample of groups and clusters of galaxies we have measured the effect of gravitational redshift produced by their host dark matter haloes. Our results shows radial velocity decrements consistent with general relativity predictions and previous measurements by Wojtak et al (2011) in clusters of galaxies. 
Mariano Javier de Le\'on Dom\'inguez Romero, Diego Garc\'ia Lambas and   Hern\'an Muriel
astro-ph.CO gr-qc