The Current Star Formation Rate of the Local Universe

The Universidad Complutense de Madrid (UCM) survey is a long-term project aimed at finding and analyzing star-forming galaxies detected by their Hα emission in Schmidt objective-prism plates. The instrumental setup limits the volume of the universe surveyed to a redshift z ≲ 0.045. So far we have discovered several hundred emission-line galaxies (ELGs) undergoing star formation at a wide range of levels. Analyzing a complete sample of ELGs from the UCM survey, we have computed the Hα luminosity function for the star-forming galaxies in the surveyed volume of the universe. A Schechter function provides a good fit to the Hα luminosity function with the following parameters: α = -1.3 ± 0.2, L*(Hα) = 1042.15±0.08 ergs s-1, and ϕ* = 10-3.2±0.2 Mpc-3 for H0 = 50 km s-1 Mpc-1. Integrating over the full range of luminosities, we obtain an Hα luminosity density of 1039.1±0.2 ergs s-1 Mpc-3. Using the Hα emission as a star formation rate (SFR) estimator, this translates into a SFR density for the local universe of 0.013−0.005+0.007 M☉ yr-1 Mpc-3 in star-forming galaxies with EW(Hα + [N II]) > 10 Å and z ≲ 0.045 for a Scalo initial mass function. This is the first observational determination of this quantity, which will provide a direct test of current galaxy formation and evolution models.