Abstract

This is the fourth of a series of papers on low X-ray luminosity galaxy clusters. The sample comprises 45 galaxy clusters with X-ray luminosities fainter than 0.7 x 104(4) erg s(-1) at redshifts lower than 0.2 in the regions of the Sloan Digital Sky Survey. The sample of spectroscopic members of the galaxy clusters was obtained with the criteria: r(p) <= 1Mpc and Delta V <= sigma using our sigma estimates containing 21 galaxy clusters with more than six spectroscopic members. We have also defined a sample of photometric members with galaxies that satisfy r(p) <= 1Mpc, and Delta V <= 6000 km s(-1) including 45 galaxy clusters with more than six cluster members. We have divided the redshift range in three bins: z <= 0.065; 0.065 < z < 0.10; and z >= 0.10. We have stacked the galaxy clusters using the spectroscopic sub-sample and we have computed the best RS linear fit within 1 sigma dispersion. With the photometric sub-sample we have added more data to the RS obtaining the photometric 1 sigma dispersion relative to the spectroscopic RS fit. We have computed the luminosity function using the 1/V-max method fitting it with a Schechter function. The obtained parameters for these galaxy clusters with low X-ray luminosities are remarkably similar to those for groups and poor galaxy clusters at these lower redshifts.