ar X iv : a st ro - p h / 98 03 00 8 v 2 5 F eb 1 99 9 Ω B and Ω 0 From MACHOs and Local Group Dynamics

8 v 1 2 M ar 1 99 8 Ω B and Ω 0 From MACHOs and Local Group Dynamics

We obtain restrictions on the universal baryon fraction, f B ≡ Ω B /Ω 0 , by assuming that the observed microlensing events towards the Large Magellanic Cloud are due to baryonic MACHOs in the halo of the Galaxy and by extracting a bound to the total mass of the Milky Way from the motion of tracer galaxies in the Local Group. We find a lower bound f B > 0.31 +0.19 −0.15. Consistency with the pr...

ar X iv : a st ro - p h / 99 02 29 8 v 2 1 3 A pr 1 99 9 New limits on Ω Λ and Ω M from old galaxies at high redshift

ar X iv : a st ro - p h / 98 08 03 4 v 1 5 A ug 1 99 8 Weighing Superclusters

We present a summary report on a detailed study of the mass and dynamical state of the Corona Borealis supercluster using the largest redshift survey of this object to date. Extensive N-body experiments are performed on simulated superclusters in both critically-flat and low-density cosmological models to test the robustness and errors of the mass estimators used on the data. From the redshifts...

ar X iv : a st ro - p h / 98 03 27 7 v 1 2 4 M ar 1 99 8 The Most Massive Distant Clusters : Determining Ω and σ 8

The existence of the three most massive clusters of galaxies observed so far at z > 0.5 is used to constrain the mass density parameter of the universe, Ω, and the amplitude of mass fluctuations, σ 8. We find Ω=0.2 −0.4 (95 %). We show that the existence of even the single most distant cluster at z=0.83, MS1054–03, with its large gravitational lensing mass, high temperature, and large velocity ...

ar X iv : a st ro - p h / 97 11 03 5 v 1 4 N ov 1 99 7 CLUSTERS IN VARIOUS COSMOLOGICAL MODELS : ABUNDANCE AND EVOLUTION

The combination of measurements of the local abundance of rich clusters of galaxies and its evolution to higher redshift offers the possibility of a direct measurement of Ω 0 with little contribution from other cosmological parameters. We investigate the significance of recent claims that this evolution indicates that Ω 0 must be small. The most recent cluster velocity dispersion function 1 fro...