The local Universe in the era of large surveys. II. Multi-wavelength characterisation of activity in S0 galaxies

Abstract

This is the second paper in a series using data from about 56,000 S0 galaxies of the local Universe (z < 0.1) retrieved from the NSA catalogue. It builds on the outcomes of the previous work, which introduced a new classification scheme for these objects based on the principal component analysis (PCA) of their optical spectrum and its projections on to the first two eigenvectors (the PC1-PC2 diagram). We provide an exhaustive characterization of the activity of present-day S0s throughout both the broad-band PC1-PC2 and narrow-line BPT/WHAN spectral classifiers, contrasting the different types of activity classes they define, and present an alternative diagram that exploits the concordance between WHAN and PCA demarcations. The analysis is extended to the mid-infrared, radio and X-ray wavelengths by crossmatching our core sample with data from the WISE, FIRST, XMM-Newton, and Chandra surveys. This has allowed us to carry out a thorough comparison of the most important activity diagnostics in the literature over different wavebands, discuss their similarities and differences, and explore the connections between them and with parameters related to star formation and black hole accretion. Among the results obtained, we highlight the finding of evidence that nebular emission from S0-Seyfert and LINER systems that are radio and X-ray emitters is not driven by star birth, while it cannot be discarded that for a number of the members of the latter class the dominant ionising radiation comes from post-AGB stars. These and other outcomes from the present work should be transferable to other morphologies.