On the preferred length scale in the anisotropy field of extragalactic IRAS sources

We investigate the existence and meaning of a preferred length in the large-scale distribution of 60-micron 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 naive 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 = 0.3-0.5 or Omega = 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.