483 research outputs found
Redshift surveys and cosmology: A summary of the Dunk Island Conference
Redshift surveys constitute one of the prime tools of observational cosmology. Imaging surveys of the whole sky are now available at a wide range of wavelengths, and provide a basis for the new generation of massive redshift surveys currently in progress. The very large datasets produced by these surveys call for new and sophisticated approaches to the analysis of large-scale structure and the galaxy population. These issues, and some preliminary results from the new redshift surveys, were discussed at the second Coral Sea Cosmology Conference, held at Dunk Island on 24-28 August 1999. This is a summary of the conference; the full conference proceedings are on the WWW at http://www.mso.anu.edu.au/DunkIsland/Proceedings
Measuring H0 from the 6dF Galaxy Survey and future low-redshift surveys
Baryon acoustic oscillations (BAO) at low redshift provide a precise and
largely model-independent way to measure the Hubble constant, H0. The 6dF
Galaxy Survey measurement of the BAO scale gives a value of H0 = 67 +/- 3.2
km/s/Mpc, achieving a 1-sigma precision of 5%. With improved analysis
techniques, the planned WALLABY (HI) and TAIPAN (optical) redshift surveys are
predicted to measure H0 to 1-3% precision.Comment: Proceedings of IAU Symposium 289, "Advancing the Physics of Cosmic
Distances", Richard de Grijs & Giuseppe Bono (eds), 2012, 4p
THE ABELL CLUSTER INERTIAL FRAME
A re-analysis of Lauer \& Postman's (1994; LP) finding that the Abell cluster
inertial frame (ACIF), defined by the 119 Abell clusters within 15,000 km/s, is
moving at almost 700 km/s with respect to the cosmic microwave background. Such
a motion is inconsistent with most cosmological models at a confidence level of
95% or higher. We obtain an exact expression for a cluster's peculiar velocity
in terms of the residual magnitude about the mean relation between the metric
luminosity of brightest cluster galaxies and the slope of their luminosity
profiles. We compare this to the approximation used by LP. We develop a maximum
likelihood procedure for recovering the Local Group motion from the scatter in
this relation which yields an unbiased estimate for the motion with
significantly smaller uncertainties than LP's method. We re-analyse LP's data
and find that the Local Group is moving relative to the ACIF at 626 (+/-242)
km/s towards l=216, b=-28 (+/-20). This implies that the ACIF is itself moving
relative to the cosmic microwave background at 764 (+/-160) km/s towards l=341,
b=49 (+/-20). This motion is consistent with that derived by LP but has a 10%
larger amplitude and 20% smaller errors, making it even harder to reconcile
with cosmological models.Comment: To appear in A.J., 20 pages, Postscript, see also
http://meteor.anu.edu.au/~colless/Preprints/ACIF.p
Accretion of the Magellanic system onto the Galaxy
Our Galaxy is surrounded by a large family of dwarf galaxies of which the most massive are the Large and Small Magellanic Clouds (LMC and SMC). Recent evidence suggests that systems with the mass of the Local Group accrete galaxies in smaller groups rather than individually. If so, at least some of the Galaxy's dwarfs may have fallen in with the LMC and SMC, and were formed as part of the Magellanic system in the nearby universe. We use the latest measurements of the proper motions of the LMC and SMC and a multicomponent model of the Galactic potential to explore the evolution of these galaxy configurations under the assumption that the Magellanic system may once have contained a number of bound dwarf galaxies. We compare our results to the available kinematic data for the local dwarf galaxies, and examine whether this model can account for recently discovered stellar streams and the planar distribution of Milky Way satellites. We find that in situations where the LMC and SMC are bound to the Milky Way, the kinematics of Draco, Sculptor, Sextans, Ursa Minor, and the Sagittarius Stream are consistent with having fallen in along with the Magellanic system. These dwarfs, if so associated, will likely have been close to the tidal radius of the LMC originally and are unlikely to have affected each other throughout the orbit. However there are clear cases, such as Carina and Leo I, that cannot be explained this way
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