  Aims. We use magnetic and non-magnetic 3D numerical simulations of solar
granulation and G-band radiative diagnostics from the resulting models to
analyse the generation of small-scale vortex motions in the solar photosphere.
Methods. Radiative MHD simulations of magnetoconvection are used to produce
photospheric models. Our starting point is a non-magnetic model of solar
convection, where we introduce a uniform magnetic field and follow the
evolution of the field in the simulated photosphere. We find two different
types of photospheric vortices, and provide a link between the vorticity
generation and the presence of the intergranular magnetic field. A detailed
analysis of the vorticity equation, combined with the G-band radiative
diagnostics, allows us to identify the sources and observational signatures of
photospheric vorticity in the simulated photosphere. Results. Two different
types of photospheric vorticity, magnetic and non-magnetic, are generated in
the domain. Nonmagnetic vortices are generated by the baroclinic motions of the
plasma in the photosphere, while magnetic vortices are produced by the magnetic
tension in the intergranular magnetic flux concentrations. The two types of
vortices have different shapes. We find that the vorticity is generated more
efficiently in the magnetised model. Simulated G-band images show a direct
connection between magnetic vortices and rotary motions of photospheric bright
points, and suggest that there may be a connection between the magnetic bright
point rotation and small-scale swirl motions observed higher in the atmosphere.
