Connecting traces of galaxy evolution: the missing core mass --
  morphological fine structure relation
  Deep exposure imaging of early-type galaxies (ETGs) are revealing the
second-order complexity of these objects, which have been long considered
uniform, dispersion-supported spheroidals. "Fine structure" features (e.g.
ripples, plumes, tidal tails, rings) as well as depleted stellar cores (i.e.
central light deficits) characterize a number of massive ETG galaxies, and can
be interpreted as the result of galaxy-galaxy interactions. We discuss how the
timescale for the evolution of cores and fine structures are comparable, and
hence it is expected that they develop in parallel after the major interaction
event which shaped the ETG. Using archival data, we compare the "depleted
stellar mass" (i.e. the mass missing from the depleted stellar core) against
the prominence of the fine structure features, and observe that they correlate
inversely. This result confirms our expectation that, while the Super Massive
Black Hole (SMBH) binary (constituted by the SMBHs of the merger progenitors)
excavates the core via three-body interactions, the gravitational potential of
the newborn galaxy relaxes, and the fine structures fade below detection
levels. We expect the inverse correlation to hold at least within the first Gyr
from the merger which created the SMBH binary; after then, the fine structure
evolves independently.
