  In this study, we investigate the impact of local stellar radiation in
cosmological zoom simulations of the formation of Milky Way-sized galaxies. We
include the radiation field as an additional feedback component that is
computed alongside gravity with a tree code in an optically thin approximation.
We resimulate the initial conditions of five Milk Way-like systems taken from
the Auriga project with and without stellar radiation, and study the effects of
local stellar radiation on several properties of the galaxies and the
circumgalactic medium (CGM). Similar to previous findings, we observe that
local stellar radiation can modify gas cooling in the circumgalactic medium and
thus suppress star formation and the surface densities of young stars and HI
gas, while having little impact on the total gas content. Even though the
magnitude of the effect we find is smaller than reported in earlier work, the
radiation field is thus clearly an important component in simulations of late
time galaxies. In particular, it also suppresses the peak of the rotation curve
and reduces the mass of the stellar bulge. In the CGM region, the young stellar
radiation exceeds the external UVB and dominates the radiation field within the
virial halo at all redshifts. Nevertheless, we find that the local stellar
radiation has overall little impact on the radial density and temperature
profile of the CGM gas. The metallicity profile is slightly reduced, however,
as well as the HI and MgII column densities within $\sim 0.3\,R_{\rm vir}$. In
contrast, we find that the OVI column density is hardly impacted by the
radiation field. Additional effects can be expected from the radiation of the
central AGN during phases of quasar activity, which has not yet been included
in the simulations of the present study.
