Introduction

Philosophy

It seems that every time a new population of extragalactic object is discovered, the first reaction of astronomers is to construct a luminosity function. Beyond sheer botany, this serves the useful purpose of giving a check on the completeness of surveys. The long-term motivation is Physics: the hope that the luminosity function and its change with redshift (the nearest we can get to an evolutionary track for a single object) will tell us something about how these spectacular sources operate. However, it has to be said that this objective remains in the far distance, despite nearly three decades of effort.

Why the radio waveband? Apart from the weight of history (radio astronomers take the blame for starting AGN research), the lack of foreground extinction and the lack of catalogue contamination by galactic objects are still very powerful advantages.

Notation

There are a few (arbitrary) conventions commonly adopted in the literature on this subject. The comoving density of objects per unit log10 power is denoted by ρ. The Hubble constant, where quoted explicitly, is given in the form h = H0/100 kms−1Mpc−1. Unless otherwise specified, Ω = 1 and h = 0.5 are assumed.

Radio astronomers' who's who

Radio astronomy takes the brutalist line of ordering the Universe according to output.