On the Unification of Radio Galaxies and Quasars

Extract

A comparison of the projected linear size evolution of extended quasars and radio galaxies are often used as a test of the radio galaxy - quasar unification schemes. If both the mentioned categories of radio sources differ to an observer only due to the various viewing directions, then their radio linear sizes are expected to evolve with redshift in the same way (Gopal-Krishna & Kulkarni, 1992). However, apart from the simplest linear size parameter L we can still determine two independent parameters assessing the asymmetry of the radio structure: Q - the arm lengths ratio; M - misalignment, which measures the apparent bending, and defined as the ratio of the displacement of the core from the source axis to the linear size. The asymmetry parameters Q and M can also be a powerful tool in the consistency test for the orientation based unification scheme as their evolutionary patterns should be the same for radio galaxies and quasars. Contrary to the linear size, they are not sensitive to the simple homological rescaling of the whole structure and hence to the age or expansion velocity of the structure.