ΩBand Ω0from 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...

The dynamics of isolated Local Group galaxies

We measured velocities of 862 individual red giant stars in seven isolated dwarf galaxies in the Local Group: NGC 6822, IC 1613, VV 124 (UGC 4879), the Pegasus dwarf irregular galaxy (DDO 216), Leo A, Cetus and Aquarius (DDO 210). We also computed velocity dispersions, taking into account the measurement uncertainties on individual stars. None of the isolated galaxies is denser than the densest...

Galaxy & Cluster Biasing from Local Group Dynamics

Comparing the gravitational acceleration induced on the Local Group of galaxies by different tracers of the underline density field we estimate, within the linear gravitational instability theory and the linear biasing ansatz, their relative bias factors. Using optical SSRS2 galaxies, IRAS (PSCz) galaxies and Abell/ACO clusters, we find bO,I ≈ 1.21 ± 0.06 and bC,I ≈ 4.3 ± 0.8, in agreement with...

WIMPs and MACHOs

MACHOs: THE PLOT THICKENS

We discuss the implications of the recent upward revision of the LMC microlensing rate by the MACHO Collaboration. We conclude: (i) A good case for the existence of baryonic dark matter in the halo has been made; (ii) The case for the existence of cold dark matter is unaffected and still compelling; and (iii) The Galactic halo is still an excellent place to search for cold dark matter particles...