Untangling galaxy components: full spectral bulge-disc decomposition
  To ascertain whether photometric decompositions of galaxies into bulges and
disks are astrophysically meaningful, we have developed a new technique to
decompose spectral data cubes into separate bulge and disk components, subject
only to the constraint that they reproduce the conventional photometric
decomposition. These decompositions allow us to study the kinematic and stellar
population properties of the individual components and how they vary with
position, in order to assess their plausibility as discrete elements, and to
start to reconstruct their distinct formation histories. An initial application
of this method to CALIFA integral field unit observations of three isolated S0
galaxies confirms that in regions where both bulge and disc contribute
significantly to the flux they can be physically and robustly decomposed into a
rotating dispersion-dominated bulge component, and a rotating low-dispersion
disc component. Analysis of the resulting stellar populations shows that the
bulges of these galaxies have a range of ages relative to their discs,
indicating that a variety of processes are necessary to describe their
evolution. This simple test case indicates the broad potential for extracting
from spectral data cubes the full spectral data of a wide variety of individual
galaxy components, and for using such decompositions to understand the
interplay between these various structures, and hence how such systems formed.
