3 Discussion and conclusions  

We have surveyed the Hydra cluster, Abell 1060, for star-forming galaxies using an objective prism technique to detect H$\alpha$ emission. We detect a total of 33 ELGs in the survey area, all of which have been identified with previously-known objects from one or more of a variety of catalogues. Radial velocities have been determined for 7 ELGs without previous determinations, and measurements have been made of global H$\alpha$ + N[II] equivalent width and flux values for 13 ELGs. For a complete galaxy sample (n=180) with $V \le 16$ within 2$^\circ$ of the cluster centre, 24 galaxies are detected in emission, of which 18 are cluster members.

In accord with previous work (MWI) we have classified the appearance of the emission as compact or diffuse. It has previously been found that compact emission is associated with a disturbed galaxy morphology, and is most likely the result of tidally-induced star formation either by galaxy-galaxy or cluster-galaxy interactions (see Moss & Whittle 1993). Furthermore the fraction of spirals in a cluster with compact emission has previously been found to correlate with cluster richness (see Moss & Whittle 1997). Using the complete galaxy sample we show that the fraction of spirals detected with compact emission in Abell 1060 is consistent with this correlation.

Finally, although the small sample of detected cluster ELGs in Abell 1060 precludes a detailed comparison of star formation rates between these cluster galaxies and corresponding types in the field, it is to be noted that at least three early-type cluster spirals (types S0 to Sa) and an elliptical have global H$\alpha$ equivalent widths greater than 20 Å, which would be anomalously high for these galaxy types in the field. This is consistent with an enhanced star formation rate in early-type cluster spirals found in previous work (Moss & Whittle 1993).

Acknowledgements

We thank V.M. Blanco who generously provided the plate material on which this study is based. SMB is supported by the Particle Physics and Astronomy Research Council. CM thanks the Institute of Astronomy, Cambridge for support during the course of this project. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, Caltech, under contract with the National Aeronautics and Space Administration. Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatories, are operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation.