Assembly bias evidence in close galaxy pairs
  The growth channel of massive galaxies involving mergers can be studied via
close pairs as putative merger progenitors, where the stellar populations of
the satellite galaxies will be eventually incorporated into the massive
primaries. We extend our recent analysis of the GAMA-based sample of close
pairs presented in Ferreras et al. to the general spectroscopic dataset of SDSS
galaxies (DR14), for which the high S/N of the data enables a detailed analysis
of the differences between satellite galaxies with respect to the mass of the
primary galaxy. A sample of approximately two thousand satellites of massive
galaxies is carefully selected within a relatively narrow redshift range
(0.07<z<0.14). Two main parameters are considered as major drivers of the star
formation history of these galaxies, namely: the stellar velocity dispersion of
the satellite ($\sigma$), as a proxy of "local" drivers, and the ratio between
the stellar mass of the satellite and the primary, $\mu=M_{\rm SAT}/M_{\rm
PRI}$, meant to serve as an indicator of environment. Consistently with the
independent, GAMA-based work, we find that satellites around the most massive
primaries appear older, at fixed velocity dispersion, with respect to
satellites of lower mass primaries. This trend is more marked in lower mass
satellites ($\sigma$~100 km/s), with SSP-equivalent age differences up to ~0.5
Gyr, and can be interpreted as a one-halo assembly bias, so that satellites
corresponding to smaller values of the mass ratio $\mu$ represent older
structures, akin to fossil groups.
