We present the result of a decomposition of the 2dFGRS galaxy overdensity field into an orthonormal basis of spherical harmonics and spherical Bessel functions .
Galaxies are expected to directly follow the bulk motion of the density field on large scales , so the absolute amplitude of the observed large-scale redshift-space distortions caused by this motion is expected to be independent of galaxy properties .
By splitting the overdensity field into radial and angular components , we linearly model the observed distortion and obtain the cosmological constraint \Omega _ { m } ^ { 0.6 } \sigma _ { 8 } = 0.46 \pm 0.06 .
The amplitude of the linear redshift-space distortions relative to the galaxy overdensity field is dependent on galaxy properties and , for L _ { * } galaxies at redshift z = 0 , we measure \beta ( L _ { * } , 0 ) = 0.58 \pm 0.08 , and the amplitude of the overdensity fluctuations b ( L _ { * } , 0 ) \sigma _ { 8 } = 0.79 \pm 0.03 , marginalising over the power spectrum shape parameters .
Assuming a fixed power spectrum shape consistent with the full Fourier analysis produces very similar parameter constraints .