The Evolution of Star-Forming Galaxies and

The Star Formation Rate Density of the Universe

J. Gallego

Departamento de Astrofísica

Universidad Complutense. 28040 Madrid, Spain.

jgm@astrax.fis.ucm.es

The measurement of the Star Formation Rate (SFR) density of the Universe as a function of look-back time is a fundamental parameter in order to understand the formation and evolution of galaxies. The current picture is that the global SFR density has dropped by about an order of magnitude from a peak at redshift of $\sim$1.5 to the current value at z=0. Using H$\alpha$ luminosity as SFR tracer, the Universidad Complutense de Madrid (UCM) Survey provided the global SFR density in the Local Universe. Because H$\alpha$ is observable in the optical only out to redshifts z<0.4, it becomes necessary to determine useful calibrations between other physical parameters as [OII]$\lambda$3727 or broad-band luminosities and the SFR specially suitable for the different types of star-forming galaxies found by deep spectroscopic surveys in redshifts up to z$\sim$3.

The fundamental parameter that determines galactic evolution is mass, not luminosity. Determining the mass function for the local star-forming galaxies results in a key contour condition to solve the problem of analyzing similar objects at different redshifts. Combining these local results with published Keck data for z$\sim$1 star-forming galaxies we conclude that star-forming galaxies at z=0 have similar SFR per unit mass and burst strengths to those at z$\sim$1, but are intrinsically less massive. These results agree qualitatively with a ``downsizing'' scenario, in which more massive galaxies form at higher redshift. The results suggest that these high-z star-forming objects may be related to local luminous starbursts.