To calculate the power spectrum, we average over the square of the Fourier components of the density contrast, so, to normalize the galaxy spectrum for total matter, we must multiply it by the square of the fraction of matter associated with galaxies, 2.
The power spectrum of a signal indicates the relative magnitudes of the frequency components that combine to make up the signal.
The data used to determine the power spectrum must reflect sufficient excitation in the signal..
The matter power spectrum describes the density contrast of the universe (the difference between the local density and the mean density) as a function of scale.
It is the Fourier transform of the matter correlation function..
In radio astronomy the power spectrum is the power as a function of radio frequency.
In cosmology it usually refers to the strength of galaxy clustering as a function of their separation, or to the strength of temperature variations in the cosmic microwave background versus angular scale..
We have constructed what we call "The Cosmic Spectrum", which represents all the sum of all the energy in the local volume of the universe emitted at different optical wavelengths of light..
The term ‘cosmological parameters’ is forever increasing in its scope, and nowadays often includes ,the parameterization of some functions, as well as simple numbers describing properties of the Universe.
The original usage referred to the parameters describing the global dynamics of the Universe, such as:
The power spectrum depends on various cosmological parameters, mostly on the matter density parameter Ωm Ω m and the expension rate H0 H 0, but also the baryons ( Ωb Ω b) and dark energy ( ΩΛ Ω Λ ).
Given these cosmological parameters, the transfer function and the resulting matter power spectrum can be calculated.
Within the ΛCDM model, the power spectrum shape depends primarily on the primordial power spectrum and on the combination Ωmh, which determines the horizon scale at matter–radiation equality, with a subdominant dependence on the baryon density.
The matter power spectrum describes the density contrast of the universe (the difference between the local density and the mean density) as a function of scale.
It is the Fourier transform of the matter correlation function.
On large scales, gravity competes with cosmic expansion, and structures grow according to linear theory.
