3. VLA structure and polarimetry of CSSs

3.1. Derived values

The values and some of the properties of these sources estimated from the VLA A-configuration images at 5, 8.4 and 15 GHz are presented in Table 1 (click here). The contents of Table 1 (click here) are as follows: Column 1: source name; Column 2: the observing frequency in MHz; Columns 3 to 5: major axis, minor axis (both in arcsec) and the PA in degrees of the restoring beam major axis; Column 6: the rms noise in the total intensity map far from the source of emission; Column 7: - the rms noise , where and are the rms noise on the blank sky in the distributions of the Stokes parameters Q and U; Column 8 component label; Columns 9 and 10: RA and Dec. of the component peak; Column 11: peak flux density (mJy) of the component; Column 12: total flux density (mJy) of the component. The total intensity images at 5 GHz for the sources listed in Table 1 (click here) except for 1741+279, 2033+187 and 2147+145 were presented in Mantovani et al. (1992). However, observational parameters and derived properties obtained from the VLA observations at 5 GHz are incorporated in Table 1 (click here) to aid the reader.

   

Source Obs. Beam C R.A. (B1950) Dec.(B1950) Flux Dens.

maj. min. PA peak total

0320+053 4885 0.42 0.41 -76 0.10 0.16 03 20 41.54 05 23 34.6 705.6 715.2

8440 0.27 0.27 47 0.06 0.07 41.54 34.2 413.9 466.9

14940 0.18 0.14 66 0.10 0.20 41.52 34.3 157.8 201.5

0358+004 4885 0.41 0.40 65 0.3 0.2 a 03 58 33.36 00 28 11.2 246.6 311.8

c 33.31 10.8 122.2 154.0

d 33.12 08.6 3.2 5.9

8440 0.30 0.28 51 0.07 0.06 a 33.35 11.3 144.4 209.5

c 33.31 10.8 87.2 107.5

d 33.11 08.7 1.0 4.5

0809-056 4885 0.43 0.37 -0.7 0.08 0.09 a 08 09 35.53 -05 40 19.3 186.2 303.6

b 35.45 19.4 2.3 2.3

c 35.19 20.2 85.4 151.2

8440 0.24 0.23 37 0.02 0.03 a 35.51 19.6 79.8 170.8

b 35.42 19.8 2.4 2.7

c 35.17 20.5 45.3 80.2

14490 0.13 0.12 42 0.06 0.13 a 35.52 19.6 23.6 66.6

b 35.42 19.7 1.7 1.7

c 35.17 20.5 18.5 27.1

1239-044 4885 0.43 0.38 -32 0.08 0.09 a 12 39 45.10 -04 29 51.2 60.2 336.8

b 44.78 54.60 291.8 634.3

8440 0.34 0.32 48 0.08 0.05 a 45.10 51.4 29.2 180.1

b 44.82 54.7 158.8 332.0

14490 0.12 0.12 45 0.10 0.18 a 45.08 51.0 3.5 72.5

b 44.82 54.7 31.2 151.4

1422+202 4885 0.46 0.36 -76 0.08 0.12 a 14 22 37.47 20 14 00.5 65.2 157.1

b 37.50 13 57.6 33.5 38.2

c 37.48 54.8 14.0 31.0

d 37.47 52.5 4.3 8.2

e 37.50 49.5 193.6 319.6

f 37.79 47.8 1.9 25.9

8440 0.30 0.27 50 0.06 0.05 a 14 22 37.47 20 14 00.5 28.6 87.1

b 14 22 37.51 13 57.5 26.6 27.0

c 37.48 57.2 7.5 21.9

d 37.48 52.45 2.5 5.0

e 37.51 49.4 102.1 209.0

f 37.76 47.9 0.8 17.4

14940 0.17 0.15 50 0.12 0.21 a 14 22 37.47 20 14 00.4 5.8 18.5

b 37.51 13 57.5 15.0 18.7

c 37.49 54.7 1.6 2.1

e 37.51 49.4 34.0 92.2

1741+279 8440 0.19 0.19 44 0.06 0.05 a 17 41 57.91 27 54 10.2 5.1 43.1

b 57.89 04.8 73.3 81.9

c 57.91 04.7 102.0 110.8

d 58.01 00.9 0.6 6.3

14490 0.17 0.16 47 0.10 0.18 a 57.91 10.3 1.9 5.7

b 57.89 04.8 41.0 48.5

c 57.91 04.7 164.9 170.7

2033+187 8440 0.34 0.21 75 0.04 0.05 20 33 18.03 18 46 40.1 174.0 178.8

14940 0.19 0.13 70 0.10 0.22 18.03 40.0 75.0 75.2

2147+145 8440 0.35 0.22 78 0.04 0.06 a 21 47 59.30 14 35 44.7 369.1 378.8

b 59.29 44.9 13.7 16.1

14940 0.19 0.13 74 0.15 0.22 a 59.30 44.7 154.6 165.1

b 59.28 45.0 4.3 4.6

   

Source O.I. z C PA RM DP DP

6 cm 3.6 cm 2 cm (1+z)² 6 cm 3.6 cm 2 cm 6-3.6 3.6-2

0358+004 G 0.426 a 0 0 4.9 9.5 0.52

0809-056 a -7 9.5 10.9 11.3 0.87 0.96

c -25 7.5 11.0 13.1 0.68 0.84

1239-044 G 0.480 a -19 -42 13.5 14.7 0.92 1.3

b 24 52 2.3 3.7 5.3 0.62 0.70

1422+202 Q 0.871 a -75 -263 6.3 6.8 7.5 0.93 0.91

b 0.8

c -28 -98 34.2 34.2 1

d -42 -147 39.0 63.3 0.62

e -39 -137 10.2 10.9 0.94 1.3

1741+279 Q 0.372 a 18.3

b 0 0 7.6 9.6 0.79

c 135 254 4.0 2.2

a: see notes on individual sources.

3.2. VLA polarimetry

The images obtained at 8.4 GHz and 15 GHz were convolved with a two-dimensional, circularly-symmetric Gaussian with a width of 0.4 arcsec. This approximates the resolution of the synthesized beam of the VLA A-array at 5 GHz. Parameters were calculated from the new images. Table 2 (click here) contains the following information: Column 1: source name; Column 2: optical identification; Column 3: the measured redshift; Column 4: component label; Columns 5 to 7: PA in degrees of the electric field vector at the peak of polarized emission (1 rms error calculated from the distribution of PAs in a small box around the peak of polarized emission) at 5, 8.4 and 15 GHz respectively; Column 8: the Rotation Measure defined as RM=d()/d() in radm^-2, where () is the PA at wavelength . The RM is estimated by fitting the points with a linear least-squares fit; when computed between two frequencies RM suffers from an ambiguity. Column 9: the RM corrected for redshift; Columns 10 to 12: polarization percentage at 5, 8.4 and 15 GHz respectively; Columns 13 and 14: the depolarization index, defined as the ratio of the fractional polarization at the longer wavelength to the fractional polarization at the shorter wavelength.

3.3. Notes on individual sources

3.3.1. 0320+053

This source appears, at best, to be only slightly resolved even at 15 GHz. At a redshift of 0.575 (Heckman et al. 1994), the linear diameter is <0.3 kpc ( km s^-1 Mpc^-1; q₀=1). There was no detection of polarized emission above the noise levels at any of the observing frequencies. The spectral index () ranges from between 5 and 8.4 GHz to between 8.4 and 15 GHz.

3.3.2. 0358+004 (3C 99)

The image obtained for 3C 99 at 8.4GHz is presented in Fig. 1 (click here) and shows the well-known asymmetric triple structure (Mantovani et al. 1990). The 8.4 GHz image shows that the polarized emission comes mainly from component A. The jet region (i.e. the region between components A and C) is also slightly polarized with the magnetic field aligned with the jet axis. The 15 GHz data were affected by interference and are not presented here. In the earlier investigation of its structure by Mantovani et al. (1990), the A component was shown to contain a hot spot with a compact bright feature which has been detected in VLBI observations. Additionally, it was suggested that component C contains the nucleus.

  
Figure 1: VLA image of 0358+004 at 8.4 GHz. contours are at -0.2, 0.2, 0.4, 0.6, 1, 2, 4, 8, 16, 32, 64, 128, 256 mJy . The peak flux density is 144.4 mJy . A vector length of 1= 10 mJy

  
Figure 2: VLA image of 0809-056 at 8.4 GHz. contours are at -0.15, 0.15, 0.3, 0.6, 1, 2, 4, 8, 16, 32, 64, 128 mJy . The peak flux density is 79.8 mJy . A vector length of 1= 10 mJy

  
Figure 3: VLA image of 0809-056 at 15 GHz. contours are at -0.3, 0.3, 0.6, 1, 2, 4, 8, 16, 32 mJy . The peak flux density is 23.6 mJy . A vector length of 1= 12.5 mJy

3.3.3. 0809-056

The two images obtained for 0809-056 at 8.4 GHz and 15 GHz (Figs. 2 (click here) and 3 (click here) respectively) confirm the double structure found at 5GHz. The point-like component labelled B is likely to be the core of the source since it has a flat spectrum. It is also not polarized at the detection threshold of the present observations with an upper limit of about 3.5 per cent at 8.4 GHz. If this is the case, the source is asymmetric, with the further component (C) more depolarized, while going from shorter to longer wavelengths, and with a larger Faraday rotation than A. The more extended features in the lobes are not seen at 2 cm. The extended emission from the lobe, which is polarized at both 6 and 4 cm, is below the detection limits at 2 cm
even in the image smoothed to the 6 cm resolution.

The magnetic field is aligned along the two components and suddenly changes direction by about in the hot spots. The spectral indices of the two lobes are as steep as 1.3-1.4.

3.3.4. 1239-044

This source shows a double lobed-structure that is asymmetric with a flux density ratio between the two lobes of about two, with lobe B being the brighter one. In Figs. 4 (click here) and 5 (click here) we present the 8.4 and 15GHz images respectively. There is no indication of a component which could be the candidate for the nucleus. In the components, the -vectors suggest a circumferential field in the outer edges of the lobes but there are significant changes in the PAs of the vectors within the lobes. The Faraday rotation is generally low, with values <100rad m^-2, over the components. There is a suggestion of a large RM in the region around RA 12 39 44.85 and Dec -04 29 54.3 in lobe B with a value of about 440rad m^-2 in the source rest frame. However, this is close to one of the regions where the PAs change significantly across the lobe, and the high RM needs to be confirmed from more sensitive observations of higher resolution. The lobe A is heavily resolved at 15GHz. The diffuse innermost part of the lobe is below the detection limit even in the smoothed image.

  
Figure 4: VLA image of 1239-044 at 8.4 GHz. contours are at -0.3, 0.3, 0.6, 1, 2, 4, 8, 16, 32, 64, 128, 256 mJy . The peak flux density is 158.8 mJy . A vector length of 1= 10 mJy

  
Figure 5: VLA image of 1239-044 at 15 GHz. contours are at -0.3, 0.3, 0.6, 1, 2, 4, 8, 16, 32 mJy . The peak flux density is 31.2 mJy . A vector length of 1= 12.5 mJy

3.3.5. 1422+202

This asymmetric source shows a long collimated one-sided jet. The core (component B) has a very low value of percentage polarization at 8GHz (Fig. 6 (click here)) which is likely to originate from the emerging part of the jet (see the 15GHz image; Fig. 7 (click here)). Polarized emission is detected all along the jet with the polarization percentage being as high as 30-60% in components C and D. The magnetic field looks quite ordered parallel to the jet axis and it changes direction in the hot spot (component E). The polarized emission at 15GHz from component E is lower than those found at lower frequencies. The reason is possibly that the emission from that component, mainly along the ridge, is resolved out or below the sensitivity of these observations. The RM along the jet is never larger than 130rad m^-2 in the source rest frame. The lobe A on the counter-jet side is less polarized. Its emission is more diffuse and is located closer to the nucleus.

  
Figure 6: VLA image of 1422+202 at 8.4 GHz. contours are at -0.2, 0.2, 0.4, 0.6, 1, 2, 4, 8, 16, 32, 64, 128 mJy . The peak flux density is 102.1 mJy . A vector length of 1= 10 mJy

  
Figure 7: VLA image of 1422+202 at 15 GHz. contours are at -0.3, 0.3, 0.6, 1, 2, 4, 8, 16, 32 mJy . The peak flux density is 34.0 mJy . A vector length of 1= 10 mJy

3.3.6. 1741+279

The image of this source at 8.4GHz (Fig. 8 (click here)) confirms the triple structure seen at 408MHz in the MERLIN map by Mantovani et al. (1992). At 15GHz (Fig. 9 (click here)) we detect only the central components and the hot spot at the end of the northern jet. The central component is resolved in the VLA observations at higher resolution. The C component has an inverted spectral index and is likely to host the nucleus of the source although it has polarized emission. The component B exhibits marginal depolarization between 15GHz to 8.4GHz while component C is more stongly polarized at the lower frequency. However, the values reported in Table 2 (click here) have to be taken with care since the two components are barely separated. Since the RMs of components B and C are consistent with small values, within the errors, the inferred magnetic field is initially along the line connecting the peaks of emission of the two components, and later changes direction gradually to point towards the northern component A. There appears to be a large bend in the jet close to the nucleus. The jet later points northwards and has a wiggling collimated structure.

  
Figure 8: VLA image of 1741+279 at 8.4 GHz. contours are at -0.2, 0.2, 0.4, 0.6, 1, 2, 4, 8, 16, 32, 64, 128 mJy . The peak flux density is 100.4 mJy . A vector length of 1= 10 mJy

  
Figure 9: VLA image of 1741+279 at 15 GHz. contours are at -0.4, 0.4, 0.6, 1, 2, 4, 8, 16, 32, 64, 128 mJy . The peak flux density is 159.4 mJy . A vector length of 1= 10 mJy

  
Figure 10: VLA image of 2147+145 at 8.4 GHz. contours are at -0.2, 0.2, 0.4, 0.6, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512 mJy . The peak flux density is 369.1 mJy

  
Figure 11: VLA image of 2147+145 at 15 GHz. contours are at -0.2, 0.2, 0.4, 1, 2, 4, 8, 16, 32, 64, 128, 256 mJy . The peak flux density is 154.6 mJy

3.3.7. 2033+187

The VLA observations confirm that 2033+187 is unresolved at the sub-arcsecond resolution scale. The emission is not polarized at the sensitivity level of these observations.

3.3.8. 2147+145

This source was found to be unresolved in previous VLA A-array observations at 5GHz and elongated along PA 159 at 15GHz (Cotton 1983). We detect a weak unresolved component north-west of the main component along a PA of 140 and separated from it by about 0.4 arcsec (Figs. 10 (click here) and 11 (click here)). This new component has a steep spectral index () and lies off-axis by about with respect to the axis of the VLBI jet (Cotton et al. 1984). No polarized emission was detected in either components.