S E M I N A R IDepartament d'Astronomia i Astrofísica
Universitat de València
Polarisation observations of Compact Steep Spectrum Sources at sub-arcsecond resolution
Istituto di Radioastronomia - INAF, Bologna, Italy
Seminari del departament d'Astronomia i Astrofísica
Dilluns 08 novembre 2010
Measurements of the polarised emission from Compact Steep-Spectrum (CSS) sources can provide important information about the physical conditions inside and around the region of radio emission. CSS sources are physically small objects with radio sizes smaller than 15 kpc that reside inside their host galaxies. The most widely accepted interpretation is that CSS galaxies are young radio sources of ages < 10^6 yr. The measurement of the physical properties of CSS sources can provide insight into the conditions at the birth of a powerful radio source and those of sources developing in dense interstellar environments. An effect on the synchrotron polarised emission produced by this magnetized thermal plasma is Faraday rotation, which is proportional to the product of electron density and the magnetic field component parallel to the direction of propagation integrated along the line of sight. The magnetized plasma responsible for Faraday rotation and depolarisation can be situated either within the source, in a foreground screen, or in both. However, there are several indications, such as the magnitudes of the RMs, the total rotation of the electric vector position angle > 90 deg without very high depolarisation, that most of the observable effects are not internal to the source, but are produced in foreground material in the vicinity of the radio synchrotron source. A model to describe the depolarisation behaviour in external screens has been discussed by Burn (1966) and later generalized by Tribble (1991). Many CSS sources have been observed mainly with radio interferometers like the VLA and the VLBA. Our investigations have provided very interesting results about the polarised state of the radio emission CSS sources.