The Hα luminosity function and star formation rate at z∼0.2

We have measured the H alpha + [N II] fluxes of the I-selected Canada-France Redshift Survey (CFRS) galaxies lying at a redshift z below 0.3 and hence derived the Ha luminosity function. The magnitude limits of the CFRS mean that only the galaxies with M-B greater than or similar to-21 mag were observed at these redshifts. We obtained a total Ha luminosity density of at least 10(39.44+/-0.04) ergs s(-1) Mpc(-3) at a mean z = 0.2 for galaxies with rest-frame EW(H alpha + [N II]) greater than or similar to 10 Angstrom. This is twice the value found in the local universe by Gallego et al. Our H alpha star formation rate, derived from Madau, is higher than the UV observations at the same z, implying a UV dust extinction of similar to 1 mag. We found a strong correlation between the Ha luminosity and the absolute magnitude in the B band: M(B-AB)=46.7-1.6 log L(H alpha). This work will serve as a basis of future studies of Ha luminosity distributions measured from optically selected spectroscopic surveys of the distant universe, and it will provide a better understanding of the physical processes responsible for the observed galaxy evolution.