The NIR versus 1.4 GHz FIRST flux density. The NIR flux pertains to the K_s-band fluxes of the NIR components (components N; Table 3) coincident with the radio structure centers. The NIR magnitudes are in the Vega system. The radio core flux density (top) pertains to the radio “core” flux density (Table 6) estimated using funtools on circular regions of approximately the same size (~2 arcsec) and centered on the NIR emission regions N (Table 3; see Sect. 5.2). The total radio flux density (bottom) pertains to the total FIRST flux density as a sum of the flux density of all the FIRST components (Table 1). The errorbar associated with the FIRST flux density corresponds to 1 ×  rms, where rms is the root mean square, a measure of the noise level in the FIRST image.