5 Conclusions

We have carried out an H$\alpha$ imaging survey of the central 1 deg² of the nearby clusters Abell 1367 and Coma. Significant H$\alpha$ emission is found associated with 41 galaxies in Abell 1367 and 22 in Coma. These data are used to estimate, for the first time, the H$\alpha$ luminosity function of 2 nearby clusters of galaxies. These LFs are found consistent with the H$\alpha$ luminosity function derived for the Virgo cluster, despite their different nature. The typical Schechter parameters: $\phi^{*} \approx 10^{0.00\pm0.07}$ Mpc^-3, $L^{*} \approx 10^{41.25\pm0.05}$ erg s^-1 and $\alpha \approx -0.70\pm0.10$ are obtained.

Figure 8: MB vs.  $\log L(\mbox{H}\alpha)$ for a large sample of Virgo galaxies. The solid line indicates the adopted fit, the dashed line shows the best fit obtained from a least squares fitting. A distance modulus of 31.7 mag was adopted to convert observed fluxes and magnitudes to luminosities and absolute magnitudes.

The best fitting parameters of the cluster LFs are significantly different from those found for field galaxies, in particular at the faint end where the cluster slope is shallower than the extrapolated slope of the field LF. However it must be stressed that the steep slope found in the field is based on relatively high luminosity points and no data are available below $\log L(\mbox{H}\alpha)\approx 40$ erg s^-1 i.e. where the cluster LFs begin to flatten out. After re-normalizing the cluster data on the field ones, the two sets of data points are found consistent within the completeness limit of the field samples. Until a deeper field LF will be available it is impossible to establish whether the apparent underabundance of low luminosity objects in clusters is a real evolutionary effect or it is an artifact due to incompleteness.

By computing the total SFR per unit volume of the cluster galaxies, and taking into account the cluster density in the local Universe, we estimate that the contribution of types 2 and 1 clusters is about 0.25% and 10.8% respectively of the SFR per unit volume of the local Universe.

Figure 9: Same as Fig. 6. We included the expected curve for the Virgo cluster assuming the B band luminosity function from Sandage et al. (1985) and the $L(\mbox{H}\alpha)~$vs. MB relationship given by Eq. (5).

Acknowledgements

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The INT is operated on the island of La Palma by the ING group, in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofísica de Canarias.