The density evolution of IRAS galaxies

A maximum likelihood test for density evolution is applied to a full-sky redshift survey of 5297 galaxies selected from the IRAS data base and flux-limited at 1.2 Jy. No evidence for evolution is found. Attention is given to important systematic errors which decrease the certainty with which evolution can be measured, namely, limited knowledge of the cosmological model, the unknown intrinsic spectral energy distribution of IRAS galaxies from 16 to 140 microns, the effect of density fluctuations, a Malmquist-like bias arising from flux errors in the IRAS Point Source Catalog, and possible incompleteness of the sample at high redshifts and low Galactic latitudes. It is shown that the Malmquist bias could result in a significant overestimation of the evolution rate, especially if the catalog has a flux limit near the completion limit of the Point Source Catalog.