EVOLUTION OF FAINT IRAS GALAXIES

Abstract

There has been some disagreement about the strength of evolution exhibited by IRAS galaxies. With a parameterisation such that the co-moving density increases as $(1+z)^P$ measurements of $P$ range from $2\pm3$ to $6.7\pm2.3$. We have recently completed a deep IRAS redshift survey which should help to clarify the situation. Paying particular attention to possible systematic effects (notably Malmquist Bias) we claim positive detection of evolution within this sample at the $3\sigma$ level. Our best estimate of the strength of evolution seen in this survey is $P=5.6\pm1.6\pm0.7$ corresponding to luminosity evolution $L(z)=L_{z=0}(1+z) ^{3.3\pm0.8\pm0.6}$. This estimate is consistent with all previous determinations of the rate of cosmological evolution of IRAS galaxies. Neither this survey nor any previous survey is sufficiently deep to distinguish between pure luminosity and pure density evolution nor between different parameterisation of these forms.