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Compact Steep Spectrum Sources (CSS) have projected linear sizes < 20 kpc and overall steep spectrum (5 ∼ v−α, α ≥ 0.6). Interactions with a dense interstellar medium may confine the CSSs and produce the high amounts of Faraday rotation that some distorted sources present. The first results of a detailed study of the multifrequency polarization properties of a sample of CSS sources with MERLIN and the VLA are presented.
3C286 (1328+307) is a powerful radio source identified with a quasar at z=0.849. There is a foreground galaxy responsible for an H I absorption line system at z=0.6922 (Brown & Roberts 1973), centered approximately 2.″5 to the southeast of 3C286. The radio source has a steep spectrum (α = −0.61, Sv ∝ vα between 1.4 and 15 GHz) which turns over at about 100 MHz. Subarcsecond resolution radio images show a misaligned triple structure, dominated by the central component (Spencer et al. 1989) which accounts for at least 95% of the total flux density at all frequencies. 3C286 is one of the strongest extragalactic sources in polarized emission (0.84 Jy at 5 GHz and 1.41 Jy at 1.4 GHz) and with a rotation measure close to 0 rad m–2 (Rudnick and Jones 1983). Hence the observed orientation of the electric field vector is essentially independent of frequency.
In this paper we report the first results of the 327 MHz VLBI survey which has been carried out in the last two years to select potential candidate sources for the future SVLBI missions and to search for directions of small scattering-“holes” in the interstellar scattering medium. During the three VLBI sessions conducted so far, we observed about 80 sources. Preliminary data analyzed from the first part of the survey shows that at least 17 out of 50 sources have compact components with a size smaller than 30 mas.
We discuss our VLBA observations at 5 and 2.7 GHz and our MERLIN observations at 1.6 and 5 GHz. A MERLIN+VLBA image provided good starting model for self-calibration and we obtained an unprecedent image of the bent jet of 3C 216. Our observations suggest the detection of strong polarization position angle variation across the observing band. If this is due to Faraday rotation then 3C216 may have a four-figure observed rotation measure, which is unlikely to be due to errors in the polarization position angle calibration.
We analyze polarization observations of 3C 147 at milliarcsecond scale which we have made with the VLBA at L, S, and C band and with the MERLIN array at K band. Several constraints placed by the observations on the physical conditions of the magnetoionic gas which produces the Faraday rotation are briefly discussed. Our data show that the Faraday rotation increases towards the VLBI core component with a maximum observed value of RM~ 4600±80 rad m−2. Such a value does not support the inclusion of 3C 147 as a source with exceedingly-high faraday rotation (SEFR), as suggested from published low-resolution observations.
VLA observations of selected FR-II jets (3C208, 3C352, 3C434, 3C9 and 3C14) between 5 and 15 GHz are used to derive astrophysical properties in the jets of these radio sources. We interpret the results as giving support for unifying schemes of radio galaxies and quasars. We have also determined the Faraday rotation for jets and counter-jet sides. Rotation measures are used to constrain the internal density and mach numbers of the jets, obtaining values similar to those of quasar jets but higher than those of radio galaxies. The radio brightness can be explained by doppler boosting of the synchrotron radiation, giving evidence for orientation effects as an origin for the Laing-Garrington effect.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html
The observational properties of knots in jets of two high-z quasars are presented and discussed. The knots along 3C9 and 3C309.1 jets have similar characteristics, suggesting that a common process may be responsible for knot formation. The knot's spectral indices tend to be flat at regions of disturbed flow and may be explained by particle re-acceleration due to small-scale shocks.
Unresolved or partially resolved regions of enhanced synchrotron emission are often found in jets of extragalactic radio sources.
The VLA has provided maps of kiloparsec-scale jets with multiple knots of arcsecond dimensions in nearby FR I sources like M87 (z=0.0043)  and NGC6251 (z=0.023)  and provided valuable information about the physics of energy transports in jets.
A considerable amount of theoretical work has been done to explain the nature of such compact structures. However, most of the published data of high-z objects show unresolved knots along their jets. Spectral index information is difficult to obtain for sources with small angular sizes (< 30″), due to practical limitations. This is most unfortunate for distant sources since only knots are bright enough to be detected within low-brightness collimated flows.
This work is an attempt to give an interpretation of MERLIN, VLA and EVN observational data at 6 and 18 cm for two high-redshift quasars with bent and knotty jets, and to describe their radio properties. In calculating distances Ho = 75 km s−1Mpc−1 and qo = 0.5 are adopted.
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