Disentangling the Evolution of S0 Galaxies Using Spectral Data Cubes
While it is fairly well accepted that S0 galaxies evolve from spiral disk systems, the mechanism by which they do so is not well determined. A number of processes, ranging from simply running out of gas to environmentally-driven gas removal, interactions and mergers, have been proposed, and the reality is probably that there are multiple routes between these two states.
One key way to explore how the disk and bulge components in S0 galaxies reached their current states is provided by studies of their spectra: stellar population analysis provides information on the sequence in which these components formed, while the kinematic information in these data holds clues to the degree of violence in the transformation process.
With the availability of large integral-field unit (IFU) spectral surveys of nearby galaxies, there is now the potential to extract this information in a systematic way, to address the questions of which evolutionary channels S0 have galaxies evolved down, and whether these channels depend on other properties of the galaxy such as its mass or environment. Accordingly, we have been developing new tools to extract optimally the information contained within such data, to isolate the spectral properties of these galaxies' disks and bulges.
Results to date are already proving interesting, with bulges of S0s in clusters systematically younger than the disks that surround them, implying a last chaotic burst of star formation near their centres in a reasonably violent transition, while those in less dense environments seem to show older bulges, consistent with star formation in a spiral galaxy simply ceasing.