A deep Hα survey of galaxies in the two nearby clusters Abell 1367 and Coma: The Hα luminosity functions

We present a deep wide field Hα, imaging survey of the central regions of the two nearby clusters of galaxies Coma and Abell 1367, taken with the WFC at the INT 2.5 m telescope. We determine for the first time the Schechter parameters of the Hα luminosity function (LF) of cluster galaxies. The Hα LFs of Abell 1367 and Coma are compared with each other and with that of Virgo, estimated using the B band LF by Sandage et al. (1985) and a L(Hα) vs. MB relation. Typical parameters of φ*≈ 100.00±0.07 Mpc-3, L* ≈ 1041.25±0.05 erg s-1 and α ≈ -0.70 ± 0.10 are found for the three clusters. The best fitting parameters of the cluster LFs differ from those found for field galaxies, showing flatter slopes and lower scaling luminosities L*. Since, however, our Hα survey is significantly deeper than those of field galaxies, this result must be confirmed on similarly deep measurements of field galaxies. By computing the total SFR per unit volume of cluster galaxies, and taking into account the cluster density in the local Universe, we estimate that the contribution of clusters like Coma and Abell 1367 is approximately 0.25% of the SFR per unit volume of the local Universe.