4C48.48

This large radio source at has the biggest asymmetry in the lobe intensities of the of the high redshift USS sources. The overall appearance of 4C48.48 is that of a triple (Figures 8a-8f), but this is misleading since the central component has a spectral index of and is spatially resolved in the higher resolution images (Figure 8g - 8l). Thus we label it B1. The easternmost outer lobe, B2, is extended and has a low surface brightness component: the UV plot at 20 cm indicates there is additional diffuse emission. The radio emission is dominated by the western lobe A, which is spatially resolved at 1.2" at all frequencies. The faint extension along the radio axis in Figure 8a and 8b can be seen as a separate knot in the higher resolution images (Figures 8g-8k). In these figures with 0.4" resolution, lobe A is bent to the south. In the high resolution 2 cm image (Figure 8j) there is an additional faint extension on the northeastern most side of lobe A. Because this component is resolved from the rest of lobe A at 2 cm but is not seen at 6cm at the same resolution, it must have a flat spectrum. Since it is also near the center of the optical identification and the apex of the bend in the radio axis it is likely to be the core.

In the polarization image (8d) the lobe is resolved into two weakly polarized components, but maintain roughly the same polarization angle. Most of the polarized flux at 20 cm comes from the Al component, with possibly a slight outward extension that includes (See zoom image in Fig 8l). At 6cm, lobe A is repolarized and all the components are luminous in the polarization image (Figure 8e). The polarization angle rotates smoothly, maintaining a direction roughly perpendicular to the radio axis as the axis is bent to the south (see zoom image in 8i and 8l). At 2cm in Fig 8f, only is polarized and the source appears unresolved. This feature is offset from the peak of the center of total intensity image in Fig 8c. The radio intensity and polarization asymmetry suggest that A is the foreground lobe and B is background lobe.

The optical identification is unfortunately 2.5" from a foreground star. The wings of the star overlap the radio galaxy morphology in all bands, distorting the appearance. A second star is also visible in the images to the southwest. The U band image is slightly contaminated by the redshifted Ly which barely enters the band on the red side, but since the morphology is distinctly different from the narrow band image, it is mostly the UV continuum at 1100 A in the rest frame. There is an extended narrow ridge line extending along the radio axis to the northeastern lobe B, from approximately the position of the radio core as discussed above. Fainter aligned continuum extends in the opposite direction to the southwest, with an outward flaring appearance. In the narrow band image the Ly is bright and extends over nearly 10" in large nebula aligned with the radio axis. The line emission is centrally peaked and smoothly distributed at 1" resolution. The V band is similar to the U band with a sharply defined alignment with the radio axis. The continuum maintains its brightness without fading along the ridge line for at least 2". In R band as we move further to the red the morphology begins to resolve into two main components, and in I band the bifurcation becomes evident, and the southwest component is more prominent. In K band 4C48.48 has become bimodal, with the northeastern component the brightest again. The K band also includes H line emission, which may contribute significantly to the morphology.

There is no question about the bifurcation feature in 4C48.48. If the radio core is at the center of it, the natural interpretation that the bifurcation is due to an obscuring disk would suggest that the aligned UV continuum is stronger on the backside of the source, towards the weaker depolarized lobe B. Confirmation of the radio core, and the detection of any submillimeter continuum would be extremely useful in aiding the interpretation.