The halo distribution of 2dF galaxies

We use the clustering results obtained by Madgwick et al. (2003) for a sample of 96 791 galaxies from the 2dF Galaxy Redshift Survey with redshift 0.01 < z < 0.15 to study the distribution of late-type and early-type galaxies within dark matter haloes of different mass. Within the framework of our models, galaxies of both classes are found to be as spatially concentrated as the dark matter within haloes, even though, while the distribution of star-forming galaxies can also allow for some steeper profiles, this is ruled out drastically in the case of early-type galaxies. We also find evidence for morphological segregation, as late-type galaxies appear to be distributed within haloes of mass-scales corresponding to groups and clusters up to about two virial radii, whereas passive objects show a preference to reside closer to the halo centre. If we assume a broken power law of the form [N-gal](M) = (m/m(0))(alpha1) for m(cut) less than or equal to m < m(0) and [N-gal](m) = (m/m(0))(α2) at higher masses to describe the dependence of the average number of galaxies within haloes on the halo mass, fits to the data show that star-forming galaxies start appearing in haloes of masses m(cut) ≃ 10(11) M., much smaller than what is obtained for early-type galaxies (m(cut) ≃ 10(12.6) M.). In the high-mass regime m ≥ m(0), [N-gal] increases with halo mass more slowly (α(2) ≃ 0.7) in the case of late-type galaxies than for passive objects which present α2 ≃ 1.1. The above results imply that late-type galaxies dominate the 2dF counts at all mass-scales. We stress that - at variance with previous statements - there is no degeneracy in the determination, of the best functional forms for ρ(r) and [N-gal], as they affect the behaviour of the galaxy-galaxy correlation function on different scales.