Optical spectroscopy and the UV luminosity function of galaxies in the Abell 1367 , Coma and Virgo clusters . ⋆

Optical spectroscopy and the UV luminosity function of galaxies in the Abell 1367, Coma and Virgo clusters. Abstract. Optical spectroscopy of 93 galaxies, 60 projected in the direction of Abell 1367, 21 onto the Coma cluster and 12 on Virgo, is reported. The targets were selected either because they were detected in previous Hα, UV or r ′ surveys. The present observations bring to 100% the redshift completeness of Hα selected galaxies in the Coma region and to 75% in Abell 1367. All observed galaxies except one show Hα emission and belong to the clusters. This confirms previous determinations of the Hα luminosity function of the two clusters that were based on the assumption that all Hα detected galaxies were cluster members. Using the newly obtained data we re-determine the UV luminosity function of Coma and we compute for the first time the UV luminosity function of A1367. Their faint end slopes remain uncertain (-2.00<α<-1.35) due to insufficient knowledge of the background counts. If 90% of the UV selected galaxies without redshift will be found in the background (as our survey indicates), the slope of UV luminosity function will be α∼-1.35, in agreement with the UV luminosity function of the field (Sullivan et al. 2000) and with the Hα luminosity functions of the two clusters (Iglesias-Paramo et al. 2002). We discover a point like Hα source in the Virgo cluster, associated with the giant galaxy VCC873, possibly an extragalactic HII region similar to the one recently observed in Virgo by Gerhard et al. (2002).