On the survival of metallicity gradients to major dry-mergers
  Using a large suite of galaxies with a variety of concentrations and
metallicity gradients, we study the evolution of non-dissipative ("dry") equal
mass mergers. Our purpose in generating these simulations is to explore how the
metallicity gradient in dry mergers depends on the structure and metallicity
gradients of the galaxies involved in the merger. Specifically, we would like
to answer: Could dry mergers lead to metallicity gradients as observed in
elliptical galaxies in the local Universe? Do dry mergers always lead to a
flattening of the initial (i.e., pre-merger) gradient? From this modeling, we
conclude that: The ratio of the remnant and the initial galaxy slopes span a
wide range of values, up to values greater than 1 (with values greater than one
resulting only when companions have gradients twice the progenitor). For a
merger between two ellipticals having identical initial metallicity slopes
(i.e., equal companion and galaxy slopes), the metallicity profile of the
remnant flattens, with a final gradient about 0.6 times the initial one.
Ellipticals can maintain their original pre-merger metallicity gradient if the
companion slope is sufficiently steep. The amount of flattening neither depends
on the characteristics of the orbit of the progenitors or on their initial
concentration. Given the diversity in outcomes of the mergers, we conclude that
dry mergers do not violate any observational constraints on the systematic
characteristics of metallicity gradients in local ellipticals. In fact, dry
mergers may be important within the context of the results of our simulations
and may explain the large scatter in gradients for massive ellipticals and the
relative paucity of massive ellipticals with no or shallow metallicity
gradients.
