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Notes for object 3C 356

10 note(s) found in NED.

1. 2000MNRAS.311....1B
Re:3C 356
3C 356 has long been a puzzle, with two equally bright infrared galaxies
separated by about 5 arcsec corresponding to the location of two radio
core-like features. The identification of the true nucleus has been a
matter of some debate, with different authors favouring the northern or
the southern galaxy for different reasons (see Best et al. 1997 for a
more complete discussion). For the current data, the slit was placed to
include both components, with zero offset corresponding to the location
of the northern galaxy (see Fig. 13). As is observed for the continuum
emission (e.g. Rigler et al. 1992, Best et al. 1997), the line emission
from the northern region is compact whilst that from the southern region
is more extended but gives a comparable integrated intensity (see also
Lacy & Rawlings 1994; McCarthy et al. 1996). The northern region shows
virtually no variation in its velocity with position, and a low velocity
width; the southern region, redshifted by about 1200 km s^-1^, shows a
steep velocity shear of 500 km s^-1^ in 3 arcsec and a slightly broader

2. 1999MNRAS.309..969H
Re:3C 356
3.39 3C 356
This high-redshift radio galaxy was observed with the ROSAT PSPC and
HRI by Crawford & Fabian (1993, 1996b). We confirm the existence of a
very weak source in the HRI observation, and our measurements are
consistent with theirs within the errors.

3. 1997MNRAS.286..241J
Re:3C 356
3.3.14 3C 356
The identification problems with this object have been discussed previously
(Eales & Rawlings 1990; Rigler et al. 1992). There are two nuclei 5 arcsec
apart, lying on a roughly north-west-southeast line. The north-west nucleus is
more compact and brighter in the optical, whereas the south-east nucleus
appears brighter in K-band images. The slit is centred on the north-west
nucleus and aligned so that the south-east nucleus falls in the slit. We
detected [O III] emission clearly in the central pixel and marginally in the
pixel 3 arcsec to the south-east. A detailed analysis of the spectrum of this
object has been published by Lacy & Rawlings (1994).

4. 1997ApJS..112..415M
Re:3C 356
3C 356 (z=1.079; Fig. 18).--Ground-based images (see, e.g., Le Fevre et al.
1988; Rigler et al. 1992; McCarthy et al. 1995) of 3C 356 show two components.
There is some uncertainty as to which of the two components contains the active
nucleus that produces 3C 356, as compact radio components have been detected at
both positions (see, e.g., Fernini et al. 1993; Pedelty et al. 1989a; Eales &
Rawlings 1990). We detect only the northwest component in our image; we do not
see the lower surface brightness component 4" to the southeast. Our image shows
structure in the northwest component: there is a high surface brightness
conelike structure and a fainter extension 0.6" to the northwest. We believe
that the component detected in our image is the true nucleus since nearly all
of the other 3CR galaxies at this redshift are detected in our images. A deeper
HST image of this object is given by Best et al. (1996a), who also conclude
that this component is the correct identification.

5. 1997A&A...325..898B
Re:3C 356
3.5. 3C 356 (z=1.086)
3C 356 has been observed with the ROSAT PSPC for 18.6 ksec and detected at the
~6{sigma} level for a total of ~30 net counts (Crawford & Fabian 1993). While
the spectrum is well fitted by a hot thermal plasma model, it is inconsistent
with an absorbed power law, Cygnus A type. It should be stressed, however, that
an unabsorbed power law with spectral index ~1.0, such as that predicted by our
IC model, gives an adequate representation of the data. By adopting this
spectral slope one derives a luminosity ~1.4x10^44^ erg s^-1^ in the 0.2-4.0 keV
energy interval. From the analysis of the PSPC data it has been suggested that
the source is extended, a good description being that of a point-like source
(with radius r<12") contributing ~20% of the flux and an extended component
approximately aligned with the radio axis. This has been confirmed by a
subsequent observation with the ROSAT HRI, which failed to detect a point source
at the position of the radio galaxy at the flux level expected from the PSPC
observation (Crawford & Fabian 1996a). These authors suggest that the most
likely interpretation of the source is that of the emission from a hot
intracluster gas in a cluster of galaxies hosting 3C 356. The radio structure
(ellipsoid semi-axis 290x70 Kpc) has been derived from the 1490 MHz map of Leahy
et al. (1989). The angular size subtended by the hot spots is ~80 arcsec. Since
3C 356 is the radio galaxy with the largest volume in our sample, the IC
contribution from the scattering of the CMB photons is expected to be important.
Assuming that the radio galaxy lies on the plane of the sky, we find that this
contribution accounts for ~37% of the soft X-ray luminosity. The inferred hidden
quasar luminosity, which would be required to account for the remaining soft
X-ray luminosity of the source, is ~3.7 L_< Q >_. The predicted angular size of
the source along the radio axis would be ~36 arcsec for an e-folding drop in the
radial luminosity profile. If the inclination of the radio axis with respect to
the line of sight is substantial, say {theta}_ax_=60^deg^, the efficiency of the
IC model increases and we expect an asymmetric source with a luminosity ratio ~3
between the two X-ray lobes. New optical spectropolarimetric data (Cimatti et a.
1997) obtained with the Keck Telescope show that the two radio-optical
components (a & b) are polarized in the UV rest frame continuum emission and
that there is a broad MgII {lambda}2800 emission line both in total and
polarized light associated with component (a), indicating that 80% of the 2800A
flux is contributed by non-stellar radiation. These authors conclude that their
observations definitely support the AGN unification model, but that it ramains
unclear which of the two components is hosting the hidden quasar: if it is
located in component (b), then its luminosity would have to be at least as high
as the maximum luminosity observed in 3C quasars, while if located in component
(a) the energy requirements would be greatly alleviated leading to a luminosity
closer to that of a typical quasar. The luminosity of the hidden quasar required
by our model is consistent with these findings.

6. 1996ApJS..106..247C
Re:3C 356
3C 356 (z=1.08; Figs. 27 and 40).--Images in both [O II] {lambda}3727 and the
continuum are given in Paper I and in Rigler et al. (1992). These images show
two components in both the lines and continuum: one is compact, the other is
very diffuse. There has been considerable uncertainty as to which component
should be identified with the nucleus of the radio source. Eales & Rawlings
(1990) and Fernini et al. (1993) report detections of both objects in the
radio. The compact component shows high-ionization emission lines (e.g.,
[Ne V] {lambda}3426), but the more diffuse component is brighter at 5 GHz. Our
spectra were taken with the slit aligned along the two components (P.A.=327).
They show a velocity difference of roughly 1200 km s^-1^ between the two, and
a strong velocity shear in the extended [O II] {lambda}3727 associated with
the diffuse object. It is unclear if one is justified in thinking of this as
one object when considering the dynamical implications of the observed

7. 1995ApJS...99...27M
Re:3C 356
3C 356 (z = 1.08; Figs. 46 and S8).-A bright foreground star makes
continuum imaging of this object quite difficult. High-resolution images
of this object are given by Le Fevre, Hammer, & Jones (1988a). This image
shows that the host galaxy is extremely nucleated. A large (4") region of
diffuse continuum lies 5" to the southeast of the nucleus. This region
has a rather flat surface brightness distribution and an integrated flux
equivalent to that of the nucleus. Our [O II] image shows that this
region has strong [O II] emission extended over similar scales. The
spatially integrated [O II] flux is also approximately equal to the core
[O II] flux. The radio source is a large (72") asymmetric double,
oriented in position angle 162^deg^ (Pedelty et al. 1989a). There is some
uncertainty regarding which of the two continuum objects contains the
nucleus of the radio source. Two core positions have been reported (Laing
et al. 1984; Pedelty et al. 1989a; Fernini et al. 1993) that correspond
to the two continuum objects. We identify the northern object as the
nucleus on the basis of its compact structure and high-ionization
spectrum. The diffuse object to the southeast has spatially resolved
emission lines with a low excitation level. Pales & Rawlings (1990)
identify the other object as the nucleus. At this point it remains
unclear which of the two objects is the true nucleus.

8. 1993MNRAS.263..936D
Re:3C 356
3C356 (Fig. A1r). K-band images of this unusual galaxy have also been
obtained by Eales & Rawlings (1990), Eisenhardt & Chokshi (1990) and
Rigler et al. (1992), while optical images have been presented by
McCarthy (1989) and Le Fevre et al. (1988b). The K-band image is
dominated by two components 5 arcsec apart. There has been some
astrometric confusion as to which of these corresponds to the compact
core of the radio source which is a large (72 arcsec) double in position
angle 161^deg^ (Leahy et al. 1989). Eisenhardt et al. (1991) and McCarthy
(1989) assumed that the radio core corresponds to the unresolved object
to the north-west, which has the bluer optical - infrared colours and is
completely dominant in the optical continuum and [O II] images (although
Le Fevre et al. asserted that it has redder optical colours than the
south-east component). In contrast, Eales & Rawlings (1990) claimed that
the radio core corresponds to the south-east component. Now two radio
cores have been detected (Fernini 1991), coincident with both candidate
identifications. As found by Rigler et al. (1992), the southern component
is elongated roughly perpendicular to the radio axis, but for the source
as a whole our image yields a position angle of 159^deg^. Although this
object has been discussed as a prime example of the alignment effect, it
is so confused and atypical that it would seem dangerous to use it to
address the alignment effect in general.

9. 1993AJ....105.1690F
Re:3C 356
3C 356
A previous radio image of 3C 356 by Pedelty et al. (1989) showed two
radio lobes with an angular separation of 72", but no core or jet. Figure
1 shows a greyscale image and Fig. 6(a) shows a total intensity contour
map of 3C 356 at 5 GHz at 0.38" resolution.
Our observations show two compact radio features, (D) and (E), in
the inner part of the source. The peak of the brighter feature, (D), is
at {alpha} = 17^h^23^m^06.955^s^ and {delta} = 51^deg^00'14.15", in
good agreement with that of the optical identification suggested by
Spinrad et al. (1985), which is at {alpha} = 17^h^23^m^06.96^s^ and
{delta} = 51^deg^00'14.1". This peak also appears to coincide with the
compact peak of the resolved 2.2 micron feature (b) detected by Eales &
Rawlings (1990) and by Eisenhardt & Choksi (1990). This coincidence does
not, however, uniquely establish the optical identification of the
extended radio structure; there is a similarly good positional agreement
between another galaxy noted by Riley et al. (1980) at
{alpha} = 17^h^23^m^06.66^s^ (+/- 0.20^s^) and
{delta} = 51^deg^00'18.2" (+/- 2.0"), the compact 2.2 micron feature (a)
in both Eales & Rawlings (1990) and Eisenhardt & Choksi (1990), and the
fainter radio peak (E) at {alpha} = 17^h^23^m^06.663^s^ and
{delta} = 51^deg^00'18.09". Rigler et al. (1992) suggest that (a/E) is
the parent of the radio structure because this galaxy has a higher
ionization spectrum. They also suggest that (b/D), which exhibits an
extended optical emission line system, is a companion galaxy that has
wandered into the path of an unseen radio jet emanating from (a/E).
Gaussian fits to our 6 cm data show that both (D) and (E) are
unresolved (Table 5). Our 3.6 cm data detect both (D) and (E) at a
resolution of 0.84" [Fig. 6(d)] with peak flux densities of 1.05 and 0.25
mJy, respectively. Thus, the 6 to 3.6 cm spectral indices
(defined by S_{nu}_ is proportional to {nu}^-{alpha}^) of (D) and (E)
are 0.1 and 1.1, respectively. (D), therefore, has the more typical
spectral index for the compact core of an extended radio galaxy,
whereas (E) has a spectral index more typical of a steep-spectrum,
compact source.
We conclude that the available data on the two compact radio
features near the center of 3C 356 do not resolve the identification
ambiguity uniquely. Instead, both (a/D) and (b/E) display several
characteristics of active galactic nuclei and it cannot yet be determined
which galaxy is responsible for the large-scale radio structure. This
ambiguity may remain until more sensitive radio images detect a large-
scale radio jet linking one of these two nuclei to the radio lobes.
Figures 6(b) and 6(c) show enlargements of the southeast and
northwest lobes of 3C 356 at the same 0.38" resolution with polarization
E vectors overlaid. The southeast lobe [Fig. 6(b)] contains three compact
structures (A, B, and C) of which (A) and (B) are of approximately equal
brightness. The northwest lobe [Fig. 6(c)] has a better defined hot spot
(F) and a much larger trail of extended emission than the southeast lobe.
The results of fitting 2-D elliptical Gaussian models to features (A),
(B), (C), and (F) are given in Table 6, along with the northwest and
southeast lobe flux densities.
Figures 6(e) and 6(f) reveal the detailed structures of the northern
and southern lobes of 3C 356 with polarization E vectors overlaid. Figure
6(g) shows a contour map of the total intensity at 20 cm at 3.9"
resolution from the B configuration.

10. 1974ApJ...191...43K
Re:3C 356
Geometry is not clean.
Two unresolved radio sources 69 arcsec apart
in position angle 161 degrees.
Star "N" of Fig. 8, which was
Wyndham, J.D. (1966) Ap. J., 144, 459
suggested identification,
is 14 arcsec [north-west] of the southern radio component.
It is a Galactic star from a spectrum by Schmidt
Macdonald, G.H., Kenerdine, S., and Neville, A.C.
(1968) MNRAS, 138, 25
and from the stellar colors (Table 4 here).
Star "M" of Figure 8 is 9 arcsec [south] of the northern
radio component and has stellar colors (Table 4).
A 200-inch image-tube plate shows no other objects
on a line joining the radio components.
There are several faint galaxies within 25 arcsec of "M"
one of which is within 2 arcsec of the northern radio component.
Can the complex be two independent sources,
one empty and the other (northern) a galaxy in a cluster?

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