Two Degree Field Galaxy Redshift Survey and Sloan Digital Sky Survey Galaxy Group Density Profiles

Abstract

We have analyzed the distribution of galaxies in groups identified in the largest redshift surveys available at present: the final release of the 2dF Galaxy Redshift Survey and the first release of the Sloan Digital Sky Survey. Our work comprises the study of the galaxy density profiles and the fraction of galaxies per spectral type as a function of the groupcentric distance. We have calculated the projected galaxy density profiles of galaxy groups using composite samples in order to increase the statistical significance of the results. Special care has been taken in order to avoid possible biases in the group identification and the construction of the projected galaxy density profile estimator. The results show that the projected galaxy density profiles obtained for both redshift surveys are in agreement with a projected Navarro, Frenk, and White prediction in the range 0.15 < r/r200 < 1, whereas a good fit for the measured profiles in the whole range of r/r200 is given by a projected King profile. We have adopted a generalized King profile to fit the measured projected density profiles per spectral type. In order to infer the three-dimensional galaxy density profiles, we deproject the two-dimensional density profiles using a deprojection method similar to that developed by Allen and Fabian. From two-dimensional and three-dimensional galaxy density profiles, we have estimated the corresponding galaxy fractions per spectral type. The two-dimensional fraction of galaxies computed using the projected profiles shows a similar segregation of galaxy spectral types as that obtained by Domínguez and coworkers for groups in the early data release of the 2dF Galaxy Redshift Survey. As expected, the trends obtained for the three-dimensional galaxy fractions show steeper slopes than those observed in the two-dimensional fractions.