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Astron. Astrophys. 325, 911-914 (1997)

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3. The images

In Fig. 1 we present the radio images for the six objects reported in Table 1. In order to highlight the magnetic field orientation, in the figures we have drawn the B-vectors rather than the E-vectors as usually found in literature, and the vector length is arbitrary.

[FIGURE] Fig. 1. The contour levels are -3, 3, 6, 12, 25, 50, 100, 200, 400, 800 [FORMULA] the rms noise. The vertical bar on the left side corresponds to a linear size of 5 Kpc. The vectors superimposed onto the contour levels are of arbitrary length and show the direction of the projected magnetic field. The cross marks the location where the polarization parameters of the extended emission have been measured. (a) [FORMULA] at 1.66 GHz in A configuration. The restoring beam is 1.2 [FORMULA] 1 arcsec in P.A. [FORMULA]. The rms noise on the image is 0.1 mJy. The peak flux is 609 mJy. (b) [FORMULA] at 1.36 GHz in B configuration. The restoring beam is 7 [FORMULA] 5 arcsec in P.A. [FORMULA]. The rms noise on the image is 0.12 mJy. The peak flux is 715 mJy. (c) 1514-241 at 1.36 GHz in B configuration. The restoring beam is 10 [FORMULA] 6 arcsec in P.A. [FORMULA]. The rms noise on the image is 0.25 mJy. The peak flux is 1847 mJy. (d) [FORMULA] at 1.66 GHz in A configuration. The restoring beam is 3 [FORMULA] 1.5 arcsec in P.A. [FORMULA]. The rms noise on the image is 0.15 mJy. The peak flux is 1156 mJy. (e) 2131-021 at 8.4 GHz in A configuration. The restoring beam is 0.3 [FORMULA] 0.3 arcsec. The rms noise on the image is 0.05 mJy. The peak flux is 1597 mJy. (f) 2240-260 at 8.4 GHz in A configuration. The restoring beam is 0.6 [FORMULA] 0.3 arcsec in P.A. [FORMULA]. The rms noise on the image is 0.1 mJy. The peak flux is 692 mJy.

By comparing the images at 5 GHz in B configuration and at 1.6/1.4 GHz in A configuration (they have comparable UV coverage and resolution), we found that the Faraday rotation is usually very small. Therefore the orientation of the B vectors in the images presented here is very close to the intrinsic one.

The radio images in Fig. 1 show various features as jets, lobes, halos and, perhaps, even hot-spots. We detected polarized emission not only in the core but, in the majority of the cases, also in the extended features. This permitted us to investigate the magnetic field geometry in regions not affected by relativistic beaming effects.

The percentage of the polarization flux density in the core is usually between [FORMULA] and 5 [FORMULA]. The polarized flux density in the extended emission (when detected) varies from a few percent to about 50  [FORMULA] across the source. The value given in Table 1 corresponds to the location of maximum brightness (excluding the core) in the polarization image and is indicated with a cross in the images. Here the polarization percentage is typically 10 - 20 %.

We presented these 6 objects because a well defined jet is clearly detected, and significant polarized emission has been revealed along most of the jet length. The observed projected magnetic field runs mostly parallel to the local jet direction. In Table 1 we show the polarization parameters and the difference between the projected B field orientation with respect to the local jet direction at the off nucleus peak position in polarized intensity. Also these numbers confirm that the magnetic field tends to be parallel to the jet direction.

In 1514-241, 1807+698, 2131-021 and 2240-260 the polarization angle drastically change in a "blob" (possibly a hot spot) at the edge of the source.

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© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998

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