ANISOTROPIES OF THE 60 MICRON IRAS GALAXY SAMPLE AT ANGULAR SCALES GAMMA-GREATER-THAN-2-DEGREES

We investigate the anisotropies in the 60 μm IRAS Point Source Catalog at all angular scales γ > 2°. We perform several different types of harmonic analysis up to the octopole terms. While the dipole amplitude is not much affected by the inclusion of higher order harmonics, the maximum direction is shifted by ∼ 30° in Galactic latitude when the octopole terms are included in a simultaneous fitting. The amplitudes of individual harmonics with l > 2 are strongly correlated, but the overall quadrupole and octopole moments are determined very well: The quadrupole-to-dipole ratio is 1.5-1.8 and steadily increases with flux in the range 0.6-20 Jy, while the octopole-to-dipole ratio is around 0.5-0.6 with no systematic flux dependence. The source-count rms fluctuation σ(γ) is found to be approximately proportional to γβ, where β depends somewhat on the range of γ and on the flux interval but always lies between -0.63 and -0.90. Restricting ourselves to angles γ > 5° and to flux intervals where at least 1000 sources are available, we find a well-defined result β = -0.66 ± 0.03, which substantially differs from the white-noise slope. We compare our results to a simple model where the cosmic structure is modeled by an isotropic field of stochastic perturbations.