A Spitzer-IRS view of early-type galaxies with cuspy/core nuclei and
  with fast/slow rotation
  The recent literature suggests that an evolutionary dichotomy exists for
early-type galaxies (Es and S0s, ETGs) whereby their central photometric
structure (cuspy versus core central luminosity profiles), and figure of
rotation (fast (FR) vs. slow (SR) rotators), are determined by whether they
formed by "wet" or "dry" mergers. We consider whether the mid infrared (MIR)
properties of ETGs, with their sensitivity to accretion processes in particular
in the last few Gyr (on average z < 0.2), can put further constraints on this
picture. We investigate a sample of 49 ETGs for which nuclear MIR properties
and detailed photometrical and kinematical classifications are available from
the recent literature. In the stellar light cuspy/core ETGs show a dichotomy
that is mainly driven by their luminosity. However in the MIR, the brightest
core ETGs show evidence that accretions have triggered both AGN and star
formation activity in the recent past, challenging a "dry" merger scenario. In
contrast, we do find, in the Virgo and Fornax clusters, that cuspy ETGs,
fainter than M$_{K_s}=-24$, are predominantly passively evolving in the same
epoch, while, in low density environments, they tend to be more active. A
significant and statistically similar fraction of both FR (38$^{+18}_{-11}$\%)
and SR (50$^{+34}_{-21}$\%) shows PAH features in their MIR spectra. Ionized
and molecular gas are also frequently detected. Recent star formation episodes
are then a common phenomenon in both kinematical classes, even in those
dominated by AGN activity, suggesting a similar evolutionary path in the last
few Gyr. MIR spectra suggest that the photometric segregation between cuspy and
core nuclei and the dynamical segregation between FR and SR must have
originated before z~0.2.
