The clustering of galaxies and groups

Abstract

We show that there are typically 8 satellites in the magnitude range -16 ≥M(_BT)≥ -18 within a projected distance of 1h(^-1)Mpc of a bright galaxy, their surface density being described by a power law of slope ~ 0.8. If the clustering of the bright galaxies is accounted for this corresponds to 4 satellites and a steeper slope. The satellite distributions around late and early type galaxies are significantly different. The bright-faint cross-correlation function has a lower amplitude than the bright autocorrelation function. However, we also find that faint satellites are more strongly clustered around bright galaxies than brighter satellites are, contradicting theoretical expectations. We look at the dynamics of satellites around Milky Way-like galaxies. The observations are consistent with galaxies having isothermal dark halos, containing ~ 10(^12)Mo out to at least 150h(^-1)kpc. The circular velocity of the halo is equal to the circular velocity of the inner parts of the bright galaxy. We place a 95% lower limit on the density of the Universe, Ω > 0.024 by assuming that all the mass in the Universe is within 150h-'kpc of bright galaxies. We confirm the Holmberg effect: an excess of satellites close to the minor axis of the bright galaxy. We show that Low Surface Brightness (LSB) galaxies have fewer close companions than High Surface Brightness galaxies. Since LSB galaxies have a low star formation rate, this is consistent with theories in which star formation is tidally triggered. We develop a method for estimating the clustering of objects of particular masses, based on the statistics of a gaussian field. This allows the clustering to be estimated in the mildly non-linear regime, giving results which are in good agreement with the results of numerical simulations. Our results lead us to suggest that objects of above and below the average mass exist in separate regions of the Universe. We demonstrate the potential