The mass function of the Las Campanas loose groups of galaxies

We have determined the mass function of loose groups of galaxies in the Las Campanas Redshift Survey. Loose groups of galaxies in the LCRS range in mass from $M \sim 10^{12}~M_{\odot}$ to $10^{15}~{M}_{\odot}$. We find that the sample is almost complete for masses in the interval $5\times 10^{13}{-}8\times 10^{14}~{M}_{\odot}$. Comparison of the observed mass function with theoretical mass functions obtained from N -body simulations shows good agreement with a CDM model with the parameters $\Omega_{\rm m} = 0.3$, $\Omega_{\Lambda} = 0.7$ and the amplitude of perturbations about $\sigma_8=0.78{-}0.87$. For smaller masses the mass function of LCRS loose groups flattens out, differing considerably from the group mass function found by Girardi & Giuricin (2000) and from mass functions obtained by numerical simulations.