Spectroscopic decomposition of the galaxy and halo of the cD galaxy NGC
  3311
  Information on the star-formation histories of cD galaxies and their extended
stellar haloes lie in their spectra. Therefore, to determine whether these
structures evolved together or through a two-phase formation, we need to
spectroscopically separate the light from each component. We present a pilot
study to use BUDDI to fit and extract the spectra of the cD galaxy NGC 3311 and
its halo in an Integral Field Spectroscopy datacube, and carry out a simple
stellar populations analysis to study their star-formation histories. Using
MUSE data, we were able to isolate the light of the galaxy and its halo
throughout the datacube, giving spectra representing purely the light from each
of these structures. The stellar populations analysis of the two components
indicates that, in this case, the bulk of the stars in both the halo and the
central galaxy are very old, but the halo is more metal poor and less
$\alpha$-enriched than the galaxy. This result is consistent with the halo
forming through the accretion of much smaller satellite galaxies with more
extended star formation. It is noteworthy that the apparent gradients in age
and metallicity indicators across the galaxy are entirely consistent with the
radially-varying contributions of galaxy and halo components, which
individually display no gradients. The success of this study is promising for
its application to a larger sample of cD galaxies that are currently being
observed by IFU surveys.
