Evolution of linear sizes

Abstract

The angular size-flux density relation for quasars is examined to discover if an inverse relation between the radio luminosity (P) and the linear size (l) replaces the need to define a size evolution. The discussion is limited to samples studied in the 178-408 MHz range, where steep spectra are observed. Angular size data in the 408 MHz range down to 55 mJy are shown to require an evolution in linear sizes of the radio sources. A numerical expression is defined for the growth rate. It is noted that models of the radio luminosity function indicate that the median luminosity of radio sources is steady in the flux density range 10-1 Jy at 408 MHz while the angular size increases by a factor of three. The median redshift in the same range of flux density increases from 0.35 to more than 1, while the angular size decreases with increasing redshift.