ABSTRACT We present a new sample of compact steep spectrum (CSS) sources with radio luminosity below 1026 W Hz-1 at 1.4 GHz; these are called low-luminosity compact (LLC) objects. The sources have been selected from the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey and observed with the multi-element radio linked interferometer network (MERLIN) at the L and C bands. The main criterion used for selection was the luminosity of the objects, and approximately one-third of the CSS sources from the new sample have a value of radio luminosity comparable to Fanaroff-Riley type 1 sources (FR Is). About 80 per cent of the sources have been resolved and about 30 per cent have weak extended emission and disturbed structures when compared with the observations of higher-luminosity CSS sources. We have studied the correlation between radio power and linear size, and the redshift with a larger sample that also included published samples of compact objects and large-scale FR IIs and FR Is. In the radio power versus linear size diagram, the LLC objects occupy the space below the main evolutionary path of radio objects. We suggest that many of these might be short-lived objects, and their radio emission may be disrupted several times before they become FR IIs. We conclude that there exists a large population of short-lived LLC objects unexplored so far, and some of these could be precursors to large-scale FR Is.
