Population Gradients in the SDSS Galaxy Catalog. The role of merging
  We investigate the role of the environment on the colour and stellar
population gradients in a local sample of ~3500 central and ~1150 satellite
SDSS early-type galaxies (ETGs). The environment is parameterized in terms of
the number of satellite galaxies, N_gal in each group. For central galaxies, we
find that both optical colour and mass-to-light (M/L) ratio gradients are
shallower in central galaxies residing in denser environments (higher N_gal).
This trend is driven by metallicity gradients, while age gradients appear to be
less dependent on the environment and to have a larger scatter. On the other
hand, satellites do not show any differences in terms of the environment. The
same results are found if galaxies are classified by central age, and both
central and satellite galaxies have shallower gradients if they are older and
steeper gradients if younger, satellites being independent of ages. In central
galaxies, we show that the observed trends can be explained with the occurrence
of dry mergings, which are more numerous in denser environments and producing
shallower colour gradients because of more uniform metallicity distributions
due to the mixing of stellar populations, while no final clues about merging
occurrence can be obtained for satellites. Finally we discuss all systematics
on stellar population fitting and their impact on the final results.
