Effelsberg contribution to the B3/VLA survey

Homogeneous databases over a wide frequency range for a large sample of radio sources with intermediate or low flux densities are an important ingredient to modern astrophysics. We have therefore embarked on a project to obtain flux densities for the B3-VLA sample over a frequency range as wide as possible. The aim is to study the spectral properties of a complete sample of radio sources. The B3-VLA sample is composed of sources that are roughly equally distributed in 5 flux density intervals, and that is 50 times fainter than the 3C survey. The sample contains 1049 radio sources. The spectral database of the whole sample comprises flux densities at 151 MHz, 327 MHz, 408 MHz, 1.4 GHz, 4.85 GHz, and 10.6 GHz.



In the above figiure we show a radio colour-colour diagram illustrating the differ-
ent population areas of radio galaxies and quasars. The high-frequency spectral index exhibits a larger spread than the low-frequency one. This is to be expected
if spectral steepening due to synchrotron and inverse Compton energy losses is important: it changes the high-frequency spectral index first, before the sources have aged sufficiently such as to affect the low-frequency one as well. The ex-
pected evolutionary track in this diagramme would be roughly speaking that re-
flected in the overall distribution of, in particular, radio galaxies: if these sources commence their lives with flat (injection) spectra, they should gradually move downward at a faster rate than leftward. Also evident in the figure is that radio galaxies (crosses) have on average steeper high-frequency spectra than quasars; in particular, they dominate the lowest part of the diagramme.

A thorough statistical analysis of the B3/VLA source survey is in progress. In particular, we are evaluating their polarization properties, along with some 200 rotation measures that will reesult from this study..