Sandro Bardelli — Page 3

arXiv2003

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

[ABRIDGED] We present the first statistical analysis of the complete ESO-Sculptor redshift survey (ESS). The flux-calibrated sample of 617 galaxy spectra with R_c<20.5 is separated into 3 spectral classes (early, intermediate, and late). We report in detail on the spectral classification, the polynomial K-corrections, and all sources of corresponding random and systematic errors. The derived luminosity functions (LF) in the Johnson-Cousins B and Rc bands are in agreement with the results from the comparable CNOC2 survey (Lin et al. 1999), whereas the ESS provides the first estimates of LFs per spectral type in the Johnson V band. A renewed interpretation of the galaxy LFs from a redshift survey are obtained by fitting the ESS LFs with composite functions based on the local LFs per morphological type (Sandage, Binggeli & Tammann 1985; Jerjen & Tammann 1997). As good or better fits than with pure Schechter functions are obtained using: for the early-type LF, a two-wing Gaussian; for the intermediate-type LF, the sum of a Gaussian modeling the Spiral galaxies and a steep Schechter function (alpha=-1.5) representing the dwarf elliptical galaxies; for the late-type LF, a similar composite function with a flat or weaker slope (-0.8 0.1 which separates the giant and dwarf galaxy populations.

astro-ph↗

arXiv2001

A study of the core of the Shapley Concentration: VI. Spectral properties of galaxies

We present the results of a study of the spectral properties of galaxies in the central part of the Shapley Concentration, covering an extremely wide range of densities, from the rich cluster cores to the underlying supercluster environment. Our sample is homogeneous, in a well defined magnitude range (17=<b_J=<18.8) and contains ~1300 spectra of galaxies at the same distance, covering an area of ~26 sq.deg. These characteristics allowed an accurate spectral classification, that we performed using a Principal Components Analysis technique. This spectral classification, together with the [OII] equivalent widths and the star formation rates, has been used to study the properties of galaxies at different densities: cluster, intercluster (i.e. galaxies in the supercluster but outside clusters) and field environment. No significant differences are present between samples at low density regimes (i.e. intercluster and field galaxies). Cluster galaxies, instead, not only have values significantly different from the field ones, but also show a dependence on the local density. Moreover, a well defined morphology-density relation is present in the cluster complexes, although these structures are known to be involved in major merging events. Also the mean equivalent width of [OII] shows a trend with the local environment, decreasing at increasing densities, even if it is probably induced by the morphology-density relation. Finally we analyzed the mean star formation rate as a function of the density, finding again a decreasing trend (at ~ 3sigma significance level). Our analysis is consistent with the claim of Balogh et al. (1998) that the star formation in clusters is depressed.

astro-ph↗