We investigate the evolution of stellar population gradients from z = 2 to z = 0 in massive galaxies at large radii ( r > 2 R _ { \mathrm { eff } } ) using ten cosmological zoom simulations of halos with 6 \times 10 ^ { 12 } M _ { \odot } < M _ { \mathrm { halo } } < 2 \times 10 ^ { 13 } M _ { \odot } .
The simulations follow metal cooling and enrichment from SNII , SNIa and AGB winds .
We explore the differential impact of an empirical model for galactic winds that reproduces the mass-metallicity relation and its evolution with redshift .
At larger radii the galaxies , for both models , become more dominated by stars accreted from satellite galaxies in major and minor mergers .
In the wind model , fewer stars are accreted , but they are significantly more metal poor resulting in steep global metallicity ( \langle \nabla Z _ { \mathrm { stars } } \rangle = -0.35 dex/dex ) and color ( e.g . \langle \nabla g - r \rangle = -0.13 dex/dex ) gradients in agreement with observations .
In contrast , colour and metallicity gradients of the models without winds are inconsistent with observations .
Age gradients are in general mildly positive at z = 0 ( \langle \nabla Age _ { \mathrm { stars } } \rangle = 0.04 dex/dex ) with significant differences between the models at higher redshift .
We demonstrate that for the wind model , stellar accretion is steepening existing in-situ metallicity gradients by about 0.2 dex by the present day and helps to match observed gradients of massive early-type galaxies at large radii .
Colour and metallicity gradients are significantly steeper for systems which have accreted stars in minor mergers , while galaxies with major mergers have relatively flat gradients , confirming previous results .
The effect of stellar migration of in-situ formed stars to large radii is discussed .
This study highlights the importance of stellar accretion for stellar population properties of massive galaxies at large radii , which can provide important constraints for formation models .