We have presented in this paper new, higher resolution radio images of a group of 14 galaxies belonging to the 2-Jy sample of radio sources. The new images improve on the data already available for these objects and, in general, the database that we are building up on the sample.
Although the radio data presented here are mainly useful in the context of the work we are doing on the sample, it is still interesting to highlight some general results that can be derived from the new data. These will be briefly described in the following sections.
From our previous studies we have found that the core dominance [i.e. ratio
between the core and the extended radio fluxes
,
in tests of unified schemes commonly used as
an indicator for the orientation of a source] appears to depend on both the
morphological classification (Morganti et al. 1995) and the optical
characteristics of the radio galaxies. Among the FRII radio galaxies, most
Narrow Line Radio Galaxies (NLRGs) show low values of
,
while BLRGs
tend to have large
(Laing et al. 1994; Morganti et al. 1997a;
Hardcastle et al. 1998) supporting the idea that BLRGs are more beamed toward
us.
What do the new radio data tell us? In the observed sample we have three BLRG:
0035-02, 1602+01, 1938-15 (two of them only recently classified as BLRG).
Both 0035-02 and 1602+01 have very prominent cores and the core flux
densities measured in the new observations are consistent with what was found
before. In particular we find R=0.33 and R=0.061 for 0035-02 and 1602+01
respectively (if using the total fluxes taken from single dish observations,
Peacock & Wall 1985). On the other hand, in 1938-15 we do not detect any
core in our higher resolution map. This sets an upper limit to the value of
R (core flux
1.5 mJy;
0.0004), well below the average value
for BLRG (
). Thus, this object appears to be an exception like
0347+05 (
)
as pointed out by Tadhunter et al. (1998).
These objects deserve some follow-up work to understand their real nature and
why they show such differences from the other BLRG.
For the objects for which we have two frequencies available, i.e. the objects
observed with ATCA, we could investigate the presence of asymmetries in the
depolarization. This asymmetry has been found in 0039-44, 0409-75 and
1938-15 and it is also notable that these are among the
highest redshift sources in the sample and they are all small (i.e.
kpc) radio sources.
No obvious correlation has been found between the depolarization and the RM(but see later for 0409-75).
If the depolarisation is produced by an external Faraday screen (as generally believed), this screen can be due to either the X-ray halo around the radio source or to gas associated with the radio galaxy itself. In the latter case, we do not have the resolution high enough (specially in the ATCA data) to investigate in detail the structure of DP and RM in the sources.
On the other hand, if the depolarisation is due to the X-ray halo around the
radio source we can estimate the Faraday dispersion ()
for our
small sources from the formula given in Garrington et al. (1991):
where DP is the
depolarization and k=0.81 if we want to obtain
in units of cm-3
G pc.
For our frequencies we derive
and we
find values of the Faraday dispersion ranging from
cm-3
G pc
for the E lobe of 0409-75 to
cm-3
G pc for the E
lobe of 0039-44. These values are typically higher than what found for
extended sources (Garrington et al. 1991; Morganti et al. 1997b) but they lie
on the established trend found by Garrington & Conway (1991) between the
linear size and the Faraday dispersion as do the CSS (Garrington & Akujor
1996). For the CSS, this result is expected if they represent simply young
version of the extended radio galaxies but living in a similar kind of
environment. In this case, the trend between size and
would represent
the radial decline of the density of the environment and the small
radio sources in our sample could be, to first order, seen as an evolved phase
of CSS on their way to becoming extended objects.
Of the three objects considered above, the only case in which both a large
depolarization and a large RM has been observed is 0409-75. It is
interesting to note that this object also shows a quite low ionization state
(e.g. [O III] 5007/[O II]
3727 = 0.19, Dickson 1997) for a galaxy of such a high radio
power. Thus, in the case of this object the weakness of [O III]
5007 could be due
to a low ionization parameter, for instance, due to an interaction between the
radio jet and a particularly rich ambient gas.
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Figure 20:
Image of 0442-28 at 6-cm.
The contour levels are:
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Figure 22:
Image of 0453-20 at 6-cm.
The contour levels are:
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Figure 24:
Image of 1602+01 at 6-cm.
The contour levels are:
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Figure 26:
Image of 2314+03 at 6-cm. The contour levels are:
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