We investigate the existence and meaning of a preferred length in the large-scale distribution of 60- \mu m IRAS sources applying three tests to the 2-dimensional distribution on the celestial sphere , involving respectively the rms fluctuation and the correlation function of the source number density , and the peak number statistics .
For HDM models we find a best value \lambda _ { 0 } = 45 - 55 h ^ { -1 } Mpc for the peak of the spectral function P ( k ) , close to the preferred wavelength \lambda = 30 - 40 h ^ { -1 } Mpc of naïve single-scale perturbation models .
A feature should indeed be generated in this range by the anticorrelation region of \xi ( r ) , although it is not detected by recent Fourier transform analyses of redshift catalogs .
Our tests provide acceptable fits for CDM models with either \Omega _ { 0 } h = 0.3 - 0.5 or \Omega _ { 0 } h = 0.1 - 0.2 , in agreement with results in current literature .
However , the quality of such fits is less satisfactory than for HDM models , with the exception of the peak number statistics , and we are not able to find a parameter interval satisfying all of our tests simultaneously .
These results may indicate that the cosmic spectrum is more complicated than the smooth shapes predicted by current theoretical models .