We present numerical simulations of the spectral evolution and emission of radio components in relativistic jets .
We compute jet models by means of a relativistic hydrodynamics code .
We have developed an algorithm ( SPEV ) for the transport of a population of non-thermal electrons including radiative losses .
For large values of the ratio of gas pressure to magnetic field energy density , \alpha _ { { } _ { B } } \sim 6 \times 10 ^ { 4 } , quiescent jet models show substantial spectral evolution , with observational consequences only above radio frequencies .
Larger values of the magnetic field ( \alpha _ { { } _ { B } } \sim 6 \times 10 ^ { 2 } ) , such that synchrotron losses are moderately important at radio frequencies , present a larger ratio of shocked-to-unshocked regions brightness than the models without radiative losses , despite the fact that they correspond to the same underlying hydrodynamic structure .
We also show that jets with a positive photon spectral index result if the lower limit \gamma _ { min } of the non-thermal particle energy distribution is large enough .
A temporary increase of the Lorentz factor at the jet inlet produces a traveling perturbation that appears in the synthetic maps as a superluminal component .
We show that trailing components can be originated not only in pressure matched jets , but also in over-pressured ones , where the existence of recollimation shocks does not allow for a direct identification of such features as Kelvin-Helmholtz modes , and its observational imprint depends on the observing frequency .
If the magnetic field is large ( \alpha _ { { } _ { B } } \sim 6 \times 10 ^ { 2 } ) , the spectral index in the rarefaction trailing the traveling perturbation does not change much with respect to the same model without any hydrodynamic perturbation .
If the synchrotron losses are considered the spectral index displays a smaller value than in the corresponding region of the quiescent jet model .