Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-01-04
Astronomy and Astrophysics
Astrophysics
9 pages with 8 figures
Scientific paper
A remarkable correlation is found in radio-loud quasars and BLLacs when the directly observed angular motions, u, of features ejected in the innermost regions of their jets are plotted on logarithmic scales versus the directly observed 15 GHz flux density, S, of their central engines: an abrupt upper envelope cut-off with a slope of 0.5 is obtained. This upper envelope and slope can be explained in a simple non-relativistic ejection model if (a), radio-loud quasars are radio standard candles and (b), for the sources defining the cut-off, the features are all ejected with similar speeds. The upper envelope is then due to the maximum projected velocity seen when the accretion disk is edge-on, and ejections are in the plane of the sky. In our simple ejection model, where S is a good measure of relative distance, the observed distribution of angular motions can be explained if the radio luminosity of the source is a function of viewing angle, increasing towards face-on. Here we show that when u is plotted versus redshift, z, the same upper envelope cut-off is seen. It is not as sharply defined, since, in this simple model, the u upper envelope will be smeared out by sources lying at different cosmological distances, z_(c). Normalizing all sources to the same distance (1 Jy) using the flux density, S, removes this smearing and improves the sharpness of the upper envelope, supporting our assumption that S is a measure of relative distance. In this model the redshift of quasars cannot be a reliable indication of their distance. (abridged)
Bell Moley B.
McDiarmid D. R.
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