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The Redshift Distribution of Flat-Spectrum
Radio Sources at Low Flux-Densities
J.P. McKean et al.
Jodrell Bank Observatory, U.K.
Gravitational lens statistics can be used to constrain the cosmo-
logical parameters providing one has a statistically complete sam-
ple. The relative size and completeness of CLASS coupled with its
stringent search criteria make it ideal for performing a lens statis-
tics analysis. A major uncertainty in the analysis is the poor sta-
tistical information known about the unlensed parent population
at low ux-densities. These sources could potentially be lensed
into the CLASS sample due to the lensing amplication.
We conducted a pseudo-survey to nd sources at low ux-densities
(5 to 12 mJy). These sources were selected in exactly the same
manner as the CLASS, S  30 mJy, sample. Objects in our nal
sample of 36 at-spectrum radio sources were observed photo-
metrically (in 6 colours) and spectroscopically depending on their
optical brightness. The aim of these observations was to obtain
redshifts which would ll the gaps in our knowledge of the red-
shift distribution at low ux-densities. These results, as well as
forming a vital part of the CLASS lens statistics analysis, will also
contribute to our understanding of the at-spectrum radio source
population at low ux-densities..
(Co-Authors I.W.A. Browne, P. Helbig, N.J. Jackson, P.N.
Wilkinson)
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