Massive galaxy merging and cosmogony

I introduce a new method to measure the galaxy-galaxy two-point projected correlation function, wp(r p) down to very small scales (kpc). These close-pair statistics provide a strict upper limit on the rate of merger events among the galaxies under consideration, and lead to constraints of the average growth rate from merging. Modern cosmology predicts that massive galaxies reside in massive halos and that these galaxies have to grow by mergers. To test these predictions, I apply this novel method to a sample of most luminous early-type galaxies in the z ∼ 0.2 Universe using the Sloan Digital Sky Survey (SDSS) Luminous Red Galaxy (LRG) sample. I measure the cross-correlation of LRGs with red and blue companions of various luminosities on very small scales and interpret these in terms of merging. I find that accretion onto LRGs is dominated by mergers of old galaxies more massive than L*. I integrate over all types of merger events and find that these massive red galaxies are growing by about 1.7% per Gyr by merging. Comparison of this result with measurements of luminosity function evolution suggests that merging can indeed account for all the growth of these galaxies since redshift z = 1.;I show that the correlation function on small scales measures the galaxy distribution within dark-matter halos in the HOD model of galaxy clustering. My measurements of the LRG auto-correlation function imply that the inner slope of the radial profile where the density of the galaxies n goes like r-tau, has tau = 2. This is much steeper than the results found by the N-body simulations for dark matter alone (tauNFW = 1). This result suggest that either the galaxies do not follow the dark matter distribution on all scales or that the baryons substantially change the dark matter profile in the very inner parts of the halos.