Three-dimensional Spectroscopy of Blue Compact Galaxies: Diagnostic Diagrams

Here we present the analysis of three-dimensional spectroscopic data of three blue compact galaxies (Mrk 324, Mrk 370, and III Zw 102). Each of the more than 22,500 spectra obtained for each galaxy has been fitted by a single Gaussian from which we have inferred the velocity dispersion (σ), the peak intensity (Ipeak), and the central wavelength (λc). The analysis shows that the σ versus Ipeak diagrams look remarkably similar to those obtained for giant extragalactic H II regions. They all present a supersonic narrow horizontal band that extends across the entire range of intensities and that results from the massive nuclear star-forming regions of each galaxy. The σ versus Ipeak diagrams also present several inclined bands of lower intensity and an even larger σ arising from the large galactic volumes that surround the main central emitting knots. We also show that the σ versus λc and λc versus Ipeak diagrams are powerful tools that are able to unveil the presence of high- and low-mass stellar clusters, and thus allow for the possibility of inferring the star formation activity of distant galaxies even if they are not spatially resolved.