We have extended our H \alpha objective prism survey of 8 low-redshift clusters ( viz .
Abell 262 , 347 , 400 , 426 , 569 , 779 , 1367 and 1656 ) to include a complete sample of early-type galaxies within 1.5 Abell radii of the cluster centres .
Of the 379 galaxies surveyed , 3 % of E , E–S0 galaxies , 6 % of S0s and 9 % of S0/a galaxies were detected in emission .
From a comparison of cluster and supercluster field galaxies , we conclude that the frequency of emission-line galaxies ( ELGs ; W _ { \lambda } \geq 20 Å ) is similar for field and cluster early-type galaxies .
A similar result has previously been obtained for galaxies of types Sa and later .
Together , these results confirm the inference of Biviano et al .
that the relative frequency of ELGs in clusters and the field can be entirely accounted for by the different mix of morphological types between the differing environments , and that , for galaxies of a given morphological type , the fraction of ELGs is independent of environment .
Detected emission is classified as ‘ compact ’ or ‘ diffuse ’ , identified as circumnuclear starburst or AGN emission and disk emission respectively .
By comparing spectroscopic data for cluster early-type ELGs with data for field galaxies from the Palomar Spectroscopic Survey of nearby galactic nuclei , we demonstrate there is modest evidence for an enhancement of compact HII emission relative to AGN emission in the early-type cluster ELGs as compared to the field .
For the cluster early-type galaxies , compact HII emission correlates strongly with a disturbed morphology .
This suggests that , as for later type cluster galaxies , this enhanced compact HII emission can readily be explained as an enhancement of circumnuclear starburst emission due to gravitational tidal interactions , most likely caused by sub-cluster merging and other on-going processes of cluster virialisation .