The 2dF galaxy redshift survey: The environmental dependence of galaxy star formation rates near clusters

We have measured the equivalent width of the Ha emission line for 11 006 galaxies brighter than Mb, = -19 (ΩΛ = 0.7, Ωm = 0.3, H0 = 70 km s-1 Mpc-1) at 0.05 < z < 0.1 in the 2dF Galaxy Redshift Survey (2dFGRS), in the fields of 17 known galaxy clusters. The limited redshift range ensures that our results are insensitive to aperture bias, and to residuals from night sky emission lines. We use these measurements to trace μ*, the star formation rate normalized to L*, as a function of distance from the cluster centre, and local projected galaxy density. We find that the distribution of μ* steadily skews toward larger values with increasing distance from the cluster centre, converging to the field…