Spectral features of SO Galaxies in low- and high-density environments

Abstract

We aim to investigate the possibility that the formation pathway of lenticular galaxies depends on the environment, using their spectra. To this end, we estimate extinction-corrected local densities for all the galaxies with z . 0:1 in the Sloan Digital Sky Survey Data Release 12 within the limits of the Legacy Survey. The local densities are cross-matched with two morphological catalogues, one in which galaxies are visually classified by Nair and Abraham (2010), and one in which morphologies are assigned by a neural network based classification by Domínguez Sánchez et al. (2018), in order to compile subsets of lenticular galaxies in low- and high-density environments. We also compute the mean spectra representative of each one of the datasets by stacking the normalized, rest-frame shifted individual spectra. The efffects of inclination biases and morphological misclassifications in these composite spectra are discussed. We find that lenticular galaxies in low-density regions are generally bluer with enhanced emission lines in comparison with their high-density counterparts. The comparative also reveals a possible excess of automatically classified S0 galaxies in low-density regions with a relevant reservoir of ionized gas and star formation activity, which may indicate contamination from Sa. In visually classified galaxies the misclassification errors involve both Sa and E and tend to be more important in galaxies with intermediate (30o < i < 60o) inclinations