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  • Print publication year: 1994
  • Online publication date: August 2010

Knots in Extragalactic Radio Jets

from I - Evidence and Implications of Anisotropy in AGN



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) [1] and NGC6251 (z=0.023) [2] 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.