The Stromlo-APM redshift survey. 2: Variation of galaxy clustering with morphology and luminosity

We present clustering measurements for samples of galaxies selected by morphological type and luminosity from the recently completed Stromlo-APM redshift survey. We find very different results between real and redshift-space estimates of the correlation function. The real space correlation function for the all-galaxies sample is well fitted on scales 0. 2-20h^-1^ Mpc by a power law with slope γᵣ_ = 1. 71 and correlation length r₀_ = 5. 1h^-1^ Mpc. In redshift space the slope is shallower, γS_ = 1. 47 and the correlation length is slightly higher, s₀_ = 59h^-1^ Mpc. Early-type galaxies are clustered more strongly by a factor 3. 5-S. 5, than late-type galaxies. In real space the slope of the correlation function for early-type galaxies is γᵣ_ = 1. 85, slightly steeper than for late types, γᵣ_ = 1. 64. In redshift space, however, early-type galaxies have a very shallow correlation function slope, γS_ = 1. 25. This implies that these early-type galaxies suffer from enhanced redshift-space distortions compared to late-type galaxies. Low-luminosity galaxies are clustered more weakly by a factor of ~2 than L^*^ and brighter galaxies on scales ~> 1h^-1^ Mpc. Also the slope of the correlation function is steeper for low-luminosity galaxies, so that the amplitude is a factor 4 lower at 10h^-1^ Mpc. No difference, however, is seen between the clustering of L^*^ and more luminous galaxies, an observation which may be hard to reconcile with some theories of biased galaxy formation. Both redshift-space and real-space clustering estimates show a similar dependence on luminosity. Our results hint that luminosity segregation may be a purely primordial effect, due to a lower bias factor for low-luminosity galaxies, whereas morphological segregation, being most apparent on scales <~ 1h^-1^ Mpc, may be enhanced by environmental factors.