STUDY OF A COMPLETE SAMPLE OF H-ALPHA EMISSION-LINE GALAXIES

Abstract

ABSTRACT The Universidad Complutense de Madrid survey is a long project with the aim of finding and analyzing star formation galaxies using the H-alpha line as the tracer for the massive star formation processes. In order to obtain a representative complete sample of such a technique, several objective prism plates were taken with the Schmidt telescope at Calar Alto Almeria (Spain). The combination of IIIaF Kodak emulsion and a RG630 filter was used for covering the red spectral region, from 6400A to a redshift of 0.045 for the H-alpha line. A compilation of descriptions and positions is presented for 272 emission-line candidates from 545 square degrees of the sky. Also apparent magnitude and equivalent width estimators are given. Spectroscopical observations were carried out for the full sample of H-alpha emission--line galaxy (ELGs) candidates. All the spectroscopic information is presented in the form of an appendix. Each ELG was classified into one of eight natural groups of star forming galaxies. The ELG types most commonly found (47%) are intermediate to low-luminosity objects with a very intense star-formation region which dominates the optical output of the galaxy. This kind of ELGs is similar to the galaxy population detected in the blue objective prism surveys, but what is more important, it was found a second population (43%) of star-forming galaxies with low ionization or high extinction properties. This ELGs group are not detected nor in the blue (University of Michigan survey) neither in other surveys (Kiso, IRAS, Markarian) using other selection techniques. Emission-line ratio diagnostic diagrams reveal that the ELGs in the different natural groups tend to have distinctly different line ratios. This suggests that the various ELGs types differ from one another in terms of metal abundance of their ionized gas, the ionization parameter and the relative importance of the starburst process in the galaxy, confirming a previous similar result found for the UM survey. There is present a trend for lower metallicities at lower luminosities. It has not been found any galaxy with metallicity lower than I Zw 18. >From the original IRAS data it was obtained for the whole sample the far-infrared fluxes. In the one hand it is necessary to apply a two-component model for reproducing the general behaviour of the UCM sample at that spectral range. In the other hand the FIR properties of a H-alpha selected sample are well differentiated against FIR-selected samples. The line+continuum flux is the main selection parameter for the UCM survey, but other secondary effects are discussed. An study of the luminosity and spatial distribution of the UCM galaxies is presented. The ELGs follow at great scale the distribution of the catalog galaxies. Using the UCM ELGs as SFR tracers a luminosity function for the SFR at the local Universe is computed. These result has important implications for our understanding of the origin of the star formation phenomena as well as the evolution of the galaxies. In the future, we propose to extend the survey to new sky regions and deeper redshifts and to quantify the SFR at the Local Universe by means of the UCM sample. The original is written in spanish.