1. Introduction
2. Observational Databases
3. Detection of Emission Line Galaxies
3.1. ELG Detection Procedure
3.2. Robustness of the Detection
4. Sample of ELGs
4.1. Equivalent Widths and Line Fluxes
4.2. Completeness of the Sample
5. SED Fitting and Models
5.1. Input of the SED-Fitting Procedure
5.2. Tests on the Input Parameters of the Models
6. Spectra
7. Results and Discussion
7.2. Gas Phase Properties
7.3. The Color of the Galaxies
7.4. Density of O-type Stars and Feedback
8. Conclusions