Density Parameter Ω0 Research Articles

Luminosity segregation as a constraint on the theory of biased galaxy formation

THE theory of biased galaxy formation with cold dark matter (CDM) is presently the most successful attempt to reproduce the distribution of galaxies in the Universe1–6, permitting a reconciliation of the observed low value of the cosmological density parameter ω0 ≤ 0.2 with the value of unity predicted by inflation. Specific tests of the bias hypothesis, namely that galaxies are more clustered than the mass1,2,4, however, have not yet led to definitive conclusions. Here we show that a systematic luminosity segregation effect in the clustering of galaxies is expected and provides an unambiguous test of the biased galaxy formation theory. We examine in detail how the clustering of galaxies correlates with their luminosity, using different biased models and numerical simulations5–7. We find that a strong effect is expected at luminosities larger than L* the characteristic luminosity of galaxies and that the amplitude of the predicted effect at these luminosities agrees with observations8. At luminosities fainter than L* however, strong limits have been put on this segregation effect9. These limits are incompatible with any biased CDM theory in which the bias parameter bb for bright galaxies is greater than 1.5 on large scales.

Evidence for a low-density inflationary universe?

The inflationary unvierse model predicts the density parameter Ω0 to be ∼ 1.0 with the cosmological constant Λ0 usually taken to be zero, whereas observational estimates give Ω0≤0.2 and Λ0∼10-57 cm−2. It was found, however, that the observed variation of angular diameter with redshift for extragalactic radio sources could be interpreted in terms of a low density universe with linear size evolution of the sources for either an inflationary model with ∧≠0 or an open model with ∧=0.

Vacuum Energy in Cosmic Dynamicsa

Annals of the New York Academy of SciencesVolume 470, Issue 1 p. 363-363 Vacuum Energy in Cosmic Dynamicsa H. J. BLOME, H. J. BLOME Sonderforschungsbereich Radioastronomie und Institut für Astrophysik und Extraterrestrische Forschung Auf dem Hügel 71 D-53 Bonn, Federal Republic of GermanySearch for more papers by this authorW. PRIESTER, W. PRIESTER Sonderforschungsbereich Radioastronomie und Institut für Astrophysik und Extraterrestrische Forschung Auf dem Hügel 71 D-53 Bonn, Federal Republic of GermanySearch for more papers by this author H. J. BLOME, H. J. BLOME Sonderforschungsbereich Radioastronomie und Institut für Astrophysik und Extraterrestrische Forschung Auf dem Hügel 71 D-53 Bonn, Federal Republic of GermanySearch for more papers by this authorW. PRIESTER, W. PRIESTER Sonderforschungsbereich Radioastronomie und Institut für Astrophysik und Extraterrestrische Forschung Auf dem Hügel 71 D-53 Bonn, Federal Republic of GermanySearch for more papers by this author First published: May 1986 https://doi.org/10.1111/j.1749-6632.1986.tb47989.x a This paper appeared in full length in: Blome, H. J. & W. Priester. 1985. Vacuum energy in cosmic dynamics. Astrophys. Space Sci.117: 327–335. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume470, Issue1Twelfth Texas Symposium On Relaivistic AstrophysicsMay 1986Pages 363-363 RelatedInformation

Vacuum energy in cosmic dynamics

The analysis of the Th/U ratio in meteorites and the evolutionary ages of globular clusters favour values of the cosmic age of (19±5)×109 yr. This evidence together with a Hubble parameterH 0>70 km s−1 Mpc−1=(14×109 yr)−1 cannot be reconciled in a Friedmann model with Λ=0. It requires a cosmological constant in the order of 10−56 cm−2, equivalent to a vacuum densityρ v =10−29 g cm−3 The Friedmann-Lemaitre models (Λ>0) with a hot big-bang have been calculated. They are based on a present value of the baryonic matter density ofρ 0=0.5×10−30 g cm−3 as derived from the primordial4He and2H abundances. For a Hubble parameter ofH 0=75 km s−1 Mpc−1, our analysis favours a set of models which can be represented by a model with Euclidean metric (density parameter Ω0=1.0, deceleration parameterq 0=−0.93, aget 0=19.7×109 yr) and by a closed model with perpetual expansion (Ω0=1.072,q 0=−1.0, aget 0=21.4×109 yr). A present density parameter close to one can indeed be expected if the conjecture of an exponential inflation of the very early universe is correct. The possible behaviour of the vacuum density is demonstrated with the help of Streeruwitz' formula in the context of the closed model with an inflationary phase at very early times.