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 gamma(r) = 1.71 and correlation length r(0) = 5.1h(-1) Mpc. In redshift space the slope is shallower, gamma(s) = 1.47 and the correlation length is slightly higher, s(0) = 5.9h(-1) Mpc. Early-type galaxies are clustered more strongly by a factor 3.5-5.5, than late-type galaxies. In real space the slope of the correlation function for early-type galaxies is gamma(r) 1.85, slightly steeper than for late types, gamma(r) 1.64. In redshift space, however, early-type galaxies have a very shallow correlation function slope, gamma(s) = 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 similar to 2 than L* and brighter galaxies on scales greater than or similar to 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 less than or similar to 1h(-1) Mpc, may be enhanced by environmental factors.