This paper presents the first results of an H \alpha imaging survey of galaxies in the central regions of the A2151 cluster .
A total of 50 sources were detected in H \alpha , from which 41 were classified as secure members of the cluster and 2 as likely members based on spectroscopic and photometric redshift considerations .
The remaining 7 galaxies were classified as background contaminants and thus excluded from our study on the H \alpha properties of the cluster .
The morphologies of the 43 H \alpha selected galaxies range from grand design spirals and interacting galaxies to blue compacts and tidal dwarfs or isolated extragalactic H ii regions , spanning a range of magnitudes of -21 \leq M _ { B } \leq - 12.5 mag .
From these 43 galaxies , 7 have been classified as AGN candidates .
These AGN candidates follow the L ( H \alpha ) vs . M _ { B } relationship of the normal galaxies implying that the emission associated with the nuclear engine has a rather secondary impact on the total H \alpha emission of these galaxies .

A comparison with the clusters Coma and A1367 and a sample of field galaxies has shown the presence of cluster galaxies with L ( H \alpha ) lower than expected for their M _ { B } , a consecuence of the cluster environment .
This fact results in differences in the L ( H \alpha ) vs . EW ( H \alpha ) and L ( H \alpha ) distributions of the clusters with respect to the field , and in cluster to cluster variations of these quantities , which we propose are driven by a global cluster property as the total mass .
In addition , the cluster H \alpha emitting galaxies tend to avoid the central regions of the clusters , again with different intensity depending on the cluster total mass .
For the particular case of A2151 , we find that most H \alpha emitting galaxies are located close to the regions with the higher galaxy density , offset from the main X-ray peak .
Overall , we conclude that both , the global cluster environment as well as the cluster merging history play a non negligible role in the integral star formation properties of clusters of galaxies .