This edge brightened double FR II type source at has
such an ultra steep
spectrum that neither lobe was even detected at 2 cm
(
). Both lobes are
roughly equivalent in brightness at both 20 cm and 6 cm, but the
eastern lobe B is fainter
with a steeper spectral index (Fig 10a,b). Both lobes have extended
emission leading to the
hot spots. A flat spectrum core (
) becomes
evident at 6 cm but must steepen
significantly by 2 cm. In the 6 cm image at higher spatial
resolution (0.4", Fig. 10k) the
unresolved core is more distinct. In this image we can see that the
radio axis is slightly
curved in a rough S shape about the core; lobe B is twice the
distance from the core as lobe
A. On the western side the jet is resolved, becoming more
luminous as it approaches the
hot spot at the end of lobe A. Lobe B is smoothly extended to the east.
In the radio polarization images (Fig 10 c and d), lobe B becomes repolarized, with a aperture measurement of DP = 1.3. This is due to extended emission in the lobe, which is more easily detected at 20 cm. The polarization angle rotates in the extended flux east of the peak at 20 cm. This component is not detected at 6 cm. In the higher resolution image (Fig 10 k), the polarization vectors are plotted, and the depolarization to the east in lobe B can be seen. In lobe A, only an unresolved hot spot is detected in polarization at either frequency, and it is strongly depolarized with a DP = 0.25. Since the jet is well defined and associated with the brighter lobe, this appears to be the foreground side in spite of the aperture measurements of the DP which would indicate differently. The depolarization measurements of lobe B are clearly affected by the extended emission and complicated by depolarization within the source and the USS.
The optical identification is in field which has a relatively bright foreground galaxy and three bright stars (Fig 1f). The object is particularly interesting because of the curved nature of the radio source. If the radio axis were simply defined as a straight line between the end of the lobes, then the optical emission in most of the bands would appear slightly mis-aligned. However, using the high resolution radio image (Fig lOk) we see that the optical images are generally well aligned with the radio axis as extrapolated smoothly in an S shape from lobe A, down the resolved jet to the core, and on towards lobe B. Thus the alignment in 4C28.58 is with the position angle of jet at the core.
However, in detail the color gradients are more complicated. The
UV continuum in the
rest frame shown in the V band image (Fig 10e) is distributed over
a large elongated region
and aligned slightly to the north of the radio axis, with
diffuse emission surrounding it. In
the R band the central contour in Fig 10f outlines a depression,
not a peak; the morphology
becomes bifurcated near the position of the radio core, with two
components closely aligned
with the radio axis. In the I band the southern of the two
components begins to dominate.
In the K band the object is slightly extended and the peak is
coincident with the bifurcation
seen in the other bands. The Ly emission line nebula in
Figure 10i is unusual. It is large
and extended, but displaced to the east from the rest of the
source. It is very diffuse with
two barely distinguishable maxima, 55 deg to the radio axis.
The HST R band (F702W) image is shown in Fig 10j. It is scaled to
the ground based
and radio images in Figures 10a - 10j. The radio galaxy is
resolved and consists of two
distinct components aligned along the curved extension of the
radio jet. These are the same
two components seen in the ground based R band image Fig 10f.
An enlarged view of the
HST image of 4C28.58 is shown in Figure 10l. The two major
components, roughly equal in
brightness, are surrounded by small faint clumps. The northern
peak, is more compact
and the slightly fainter of the two sources. The southern
peak
is more extended. Are
the faint structures real? Note that the faint artifacts from
deconvolution that can be seen
in star
are at much fainter level relative to the peak in intensity.
A crucial issue is the position of these components relative to
the radio core. The
astrometry is hindered because of the brightness of the stars
in the field; they are saturated
on the ground based images and in the HST image. The registration of
the various optical
and HST images is not affected since fainter objects in the field
can be used. However,
the absolute positioning to the radio coordinates is probably not
better than 0.5". Thus
although the nominal astrometry puts the radio core near the a
position between and
, it could also plausibly be coincident with the southern
component
. This would
place the northern component
on the apparent foreground
side based on the resolved jet
and the radio lobe intensity asymmetry as discussed above.
The object has more extended emission along the east side than the west side, and although the large emission line nebulae is on a larger scale, it is noteworthy that the peculiar misalignment of the nebulae is on the eastern side too. The nebulae must be illuminated by some source of UV photons, so either the emission line gas or the illumination (or both) is asymmetric. If an asymmetric distribution of gas were responsible for bending the radio jet, the why is the southern jet bent also?
A series of clumps or companions are visible around the source. On
the north side of
is a ridge line that points to
along the radio axis.
The
component has an arc
like feature, centered about the peak of
, and perhaps there
is another very faint arc like
feature further away. The
and
components might all be
parts of an interrupted arc -
they lie roughly along a similar curve. Note there is no evidence of
a lensed radio core. The
"gap" in this "arc" lies roughly in the same plane as the
bifurcation in the main object.