Clocking the formation of today's largest galaxies: Wide field integral
  spectroscopy of Brightest Cluster Galaxies and their surroundings
  The formation and evolution of local brightest cluster galaxies (BCGs) is
investigated by determining the stellar populations and dynamics from the
galaxy core, though the outskirts and into the intracluster light (ICL).
Integral spectroscopy of 23 BCGs observed out to 4 r_e is collected and high
signal-to-noise regions are identified. Stellar population synthesis codes are
used to determine the age, metallicity, velocity, and velocity dispersion of
stars within each region. The intracluster light (ICL) spectra are best modeled
with populations that are younger and less metal-rich than those of the BCG
cores. The average BCG core age of the sample is 13.3$\pm$ 2.8 Gyr and the
average metallicity is [Fe/H] = 0.30 $\pm$ 0.09, whereas for the ICL the
average age is 9.2$\pm$3.5 Gyr and the average metallicity is [Fe/H] =
0.18$\pm$0.16. The velocity dispersion profile is seen to be rising or flat in
most of the sample (17/23), and those with rising values reach the value of the
host cluster's velocity dispersion in several cases. The most extended BCGs are
closest to the peak of the cluster's X-ray luminosity. The results are
consistent with the idea that the BCG cores and inner regions formed quickly
and long ago, with the outer regions and ICL forming more recently, and
continuing to assemble through minor merging. Any recent star formation in the
BCGs is a minor component, and is associated with the cluster cool core status.
