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Description
We present results of an H{alpha} survey in the rich cluster A 1689 at z=0.18, using the LDSS++ spectrograph on the Anglo-Australian Telescope (AAT). We obtained spectra covering redshifted H{alpha} at z=0.16-0.22, for 522 galaxies brighter than I=22.5, covering a field of 8.7x8.7arcmin^2^ (~1.1x1.1h^-1^Mpc at z=0.18). We securely detect H{alpha} emission in 46 of these galaxies; accounting for selection effects arising from sampling and cluster membership, we determine that 24+/-4 per cent of cluster members brighter than M_R_=-16.5+5logh are detected with H{alpha} flux greater than 4h^-2^x10^38^erg/s. From a Hubble Space Telescope mosaic covering 7.5x10.0arcmin, we determine morphologies for 199 galaxies brighter than I=21, and find that ~20 per cent of the cluster members are of type Sa or later. More than 90 per cent of cluster spirals show H{alpha} emission, compared with less than 10 per cent of E and S0 galaxies.
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