A spectroscopic analysis of the whole sample of Hα Emission-Line Galaxies (ELGs) contained in the lists 1 & 2 of the Universidad Complutense de Madrid (UCM) objectiveprism survey is presented. A significant fraction (59%) of star-forming galaxies with low ionization or high extinction properties has been found. This kind of ELG is only incompletely detected in the blue or in other ELG surveys. We have found evidence for evolution among some of the different ELG classes. A comparison between the populations detected by Case, Kiso, UM and UCM surveys is presented. We conclude that a deep Hα survey is better able to sample all the ages, evolutionary stages and luminosities of current star-forming galaxies than other surveys using blue-emission lines or colors. Finally, the luminosity and spatial distributions of the UCM galaxies are determined. The contribution of the newly found current star-forming ELGs adds new clues to galaxy evolution and has to be taken into account when trying to consider the density of ELGs and total Star Formation Rate in the Universe.

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Abstract. -We present the results of Thuan & Gunn r CCD imaging observations of the Universidad Complutense de Madrid (UCM) sample of emission-line galaxies (ELGs), selected by the presence of H a emission in low-resolution objective prism spectra. In this work we characterize photometrically and morphologically a total of 212 objects from the UCM survey. This Paper presents the observations and basic reductions, and lists a set of photometric parameters calculated for each UCM object. In addition, for the first time in a ELGs sample, we have determined the morphological classification of the objects using simultaneously five different criteria.