We study the occupation statistics of galaxies in dark matter haloes using galaxy groups identified from the 2-degree Field Galaxy Redshift Survey with the halo-based group finder of Yang et al .
( 2004b ) .
The occupation distribution is considered separately for early and late type galaxies , as well as in terms of central and satellite galaxies .
The mean luminosity of the central galaxies scales with halo mass approximately as L _ { c } \propto M ^ { 2 / 3 } for haloes with masses M < 10 ^ { 13 } h ^ { -1 } \ > { M _ { \odot } } , and as L _ { c } \propto M ^ { 1 / 4 } for more massive haloes .
The characteristic mass of 10 ^ { 13 } h ^ { -1 } \ > { M _ { \odot } } is consistent with the mass scale where galaxy formation models suggest a transition from efficient to inefficient cooling .
Another characteristic halo mass scale , M \sim 10 ^ { 11 } h ^ { -1 } \ > { M _ { \odot } } , which can not be probed directly by our groups , is inferred from the conditional luminosity function ( CLF ) that matches the observed galaxy luminosity function and clustering .
For a halo of given mass , the distribution of L _ { c } is rather narrow .
Detailed comparison with mock galaxy redshift surveys indicates this implies a fairly deterministic relation between L _ { c } and halo mass .
The satellite galaxies , however , are found to follow a Poissonian number distribution , in excellent agreement with the occupation statistics of dark matter subhaloes .
This provides strong support for the standard lore that satellite galaxies reside in subhaloes .
The central galaxies in low-mass haloes are mostly late type galaxies , while those in massive haloes are almost all early types .
We also measure the CLF of galaxies in haloes of given mass .
Over the mass range that can be reliably probed with the present data ( 13.3 \la { log } [ M / ( h ^ { -1 } \ > { M _ { \odot } } ) ] \la 14.7 ) , the CLF is reasonably well fit by a Schechter function .
Contrary to recent claims based on semi-analytical models of galaxy formation , the presence of central galaxies does not show up as a strong peak at the bright end of the CLF .
The CLFs obtained from the observational data are in good agreement with the CLF model obtained by matching the observed luminosity function and large-scale clustering properties of galaxies in the standard \Lambda CDM model .