The fraction of matter in voids

Abstract

view Abstract Citations (22) References (48) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Fraction of Matter in Voids Einasto, Jaan ; Saar, Enn ; Einasto, Maret ; Freudling, Wolfram ; Gramann, Mirt Abstract Evacuation of matter from voids is investigated using numerical simulations. Cold dark matter-type and simple power-law models with different density parameters and scales are used. The density distribution of model samples is compared with the distribution of observed samples of galaxies. Our goal is to restore the actual distribution of matter from the observed distribution of galaxies as accurately as possible. Based on the assumptions that the dominating constituent of the universe is dark matter, and that in systems of galaxies the dark matter is concentrated approximately as strongly as visible galaxies, we calculate from the discrete distribution of particles and galaxies continuous density fields using a smoothing length not exceeding the characteristic radius of systems of galaxies. We compare the mass-weighted density distributions of model and real samples and find that they are different. Models contain a smooth population of particles in low-density regions which has no counterpart in the observed distribution of galaxies; in other words, galaxies do not follow the matter distribution in the whole range of densities. This disagreement between modeled matter distributions and the observed galaxy distribution does not depend on the details of the considered models but is a generic feature of the range of models considered in this paper. However, the disagreement is a feature of the smoothing scale we chose to investigate here. To simulate the observed distribution of galaxies, the distribution of matter in models is truncated at a certain threshold density. We demonstrate that the threshold density is equal to the mean density of matter. Particles in high-density regions can be identified with the clustered population, including dark coronae around galaxies and clusters. Particles in low-density regions form the void population. During the evolution particles flow from low-density regions to high- density ones. In the present epoch approximately 15% of matter lies in voids and 85% of matter forms the clustered population. This result poses a problem for some cosmological models, since the density of the clustered population is according to available estimates {OMEGA}_c_ ~ 0.15 of the critical cosmological density, and the total density including the matter in voids is {OMEGA}_matter_~ 0.20. Possibilities to hide some dark matter in intermediate-density regions are discussed. It is demonstrated that the fraction of matter in the clustered population, F_c_, is related to the conventional biasing parameter via b = 1/F_c_. Thus, the biasing parameter cannot be considered as a free parameter; its value is determined by the data discussed above. The value of the biasing parameter depends on the smoothing scale; for our adopted scale 1.2 h^-1^ Mpc, b ~ 1..18. Publication: The Astrophysical Journal Pub Date: July 1994 DOI: 10.1086/174336 Bibcode: 1994ApJ...429..465E Keywords: Astronomical Models; Cosmology; Dark Matter; Density Distribution; Evacuating; Fractions; Galactic Evolution; Matter (Physics); Universe; Voids; Computer Programs; Computerized Simulation; Data Smoothing; Numerical Analysis; Astrophysics; COSMOLOGY: THEORY; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE; GALAXIES: CLUSTERING; METHODS: NUMERICAL full text sources ADS |