The ESO-Sculptor Survey: Luminosity functions of galaxies per spectral type at redshifts 0.1-0.5

We present the first statistical analysis of the complete ESO-Sculptor Survey (ESS) of faint galaxies. The flux-calibrated sample of 617 galaxies with R-c less than or equal to 20.5 is separated into 3 spectral classes, based on a principal component analysis which provides a continuous and template-independent spectral classification. We use an original method to estimate accurate K-corrections: comparison of the ESS spectra with a spectral library using the principal component analysis allows us to extrapolate the missing parts of the observed spectra at blue wavelengths, then providing a polynomial parameterization of K-corrections as a function of spectral type and redshift. We also report on all sources of random and systematic errors which affect the spectral classification, the K-corrections, and the resulting absolute magnitudes. We use the absolute magnitudes to measure the Johnson-Cousins B, V, R-c luminosity functions of the ESS as a function of spectral class. The shape of the derived luminosity functions show marked differences among the 3 spectral classes, which are common to the B, V, R-c bands, and therefore reflect a physical phenomenon: for galaxies of later spectral type, the characteristic magnitude is fainter and the faint-end is steeper. The ESS also provides the first estimates of luminosity functions per spectral type in the V band. The salient results are obtained by fitting the ESS luminosity functions with composite functions based on the intrinsic luminosity functions per morphological type measured locally by Sandage et al. ( 1985) and Jerjen & Tammann ( 1997). The Gaussian luminosity functions for the nearby Spiral galaxies can be reconciled with the ESS intermediate and late-type luminosity functions if the corresponding classes contain an additional Schechter contribution from Spheroidal and Irregular dwarf galaxies, respectively. The present analysis of the ESS luminosity functions offers a renewed interpretation of the galaxy luminosity function from redshift surveys. It also illustrates how luminosity functions per spectral type may be affected by morphological type mixing, and emphasizes the need for a quantitative morphological classification at z greater than or similar to 0.1 which separates the giant and dwarf galaxy populations.