The power spectrum in nearby superclusters

Abstract

The power spectrum of the distribution of galaxies in the Virgo, Coma and Perseus superclusters and their environment is studied. On scales of |$3-20\,{h}^{-1}$| Mpc the distribution of faint and normal galaxies in the Virgo supercluster is similar in a wide interval of absolute magnitudes from –15 to –19. Galaxies brighter than –19 mag basically populate high-density regions; the amplitudes of the spectra in the Virgo, Coma and Perseus superclusters are similar for galaxies of the same luminosity. On larger scales the amplitude of the power spectrum of normal and bright galaxies coincides, up to an absolute magnitude of about – 20. The power spectra of all galaxies over the interval |$1-80 \,{h}^{-1}$| Mpc in the directions of the northern and southern galactic hemispheres are analysed. In both regions the spectrum can be expressed as a combination of two power laws, with a transition scale at 10 h–1 Mpc. On larger scales the spectrum is steeper with an index |$n \approx -1.8$|⁠, on smaller scales the spectrum is flatter, with |$n \approx -1.0$|⁠. On large scales the shape of the power spectrum of galaxies is different from the one predicted by the Cold Dark Matter (CDM) model with Ω = 1. It coincides with the shape of the spectrum in the low-density CDM model with |${\Omega }_{0} = 0.2$|⁠. On smaller scales the spectral index of – 1.0 is determined by non-linear dynamical evolution. The transition scale between different regions is determined by the amplitude of the spectrum of all matter. The fluctuations on 10 h–1 Mpc scales enter the non-linear regime when the amplitude of the matter spectrum is substantially smaller than the amplitude of the spectrum of galaxies.