9,249 research outputs found
Numerical action reconstruction of the dynamical history of dark matter haloes in N-body simulations
We test the ability of the numerical action method (NAM) to recover the
individual orbit histories of mass tracers in an expanding universe in a region
of radius 26Mpc/h, given the masses and redshift-space coordinates at the
present epoch. The mass tracers are represented by dark matter haloes
identified in a high resolution N-body simulation of the standard LCDM
cosmology. Since previous tests of NAM at this scale have traced the underlying
distribution of dark matter particles rather than extended haloes, our study
offers an assessment of the accuracy of NAM in a scenario which more closely
approximates the complex dynamics of actual galaxy haloes. We show that NAM can
recover present-day halo distances with typical errors of less than 3 per cent,
compared to 5 per cent errors assuming Hubble flow distances. The total halo
mass and the linear bias were both found to be constained at the 50 per cent
level. The accuracy of individual orbit reconstructions was limited by the
inability of NAM, in some instances, to correctly model the positions of haloes
at early times solely on the basis of the redshifts, angular positions, and
masses of the haloes at the present epoch. Improvements in the quality of NAM
reconstructions may be possible using the present-day three-dimensional halo
velocities and distances to further constrain the dynamics. This velocity data
is expected to become available for nearby galaxies in the coming generations
of observations by SIM and GAIA.Comment: 12 pages, 9 figures. submitted to MNRA
Phenomenology of the Invisible Universe
Cosmology is operating now on a well established and tightly constraining
empirical basis. The relativistic LambdaCDM hot big bang theory is consistent
with all the present tests; it has become the benchmark. But the many open
issues in this subject make it reasonable to expect that a more accurate
cosmology will have more interesting physics in the invisible sector of the
universe, and maybe also in the visible part.Comment: Proceedings of 'Invisible Universe International Conference', Paris,
June 29- July 3, 200
Discovery of the Hot Big Bang: What happened in 1948
The idea that the universe is filled with the thermal radiation now termed
the Cosmic Microwave Background was first discussed in eleven publications in
the year 1948. These papers offer a detailed example of the process of
development of a new and now very productive line of research, and of the
confusion that can attend new ideas. The confusion in this case left a common
misunderstanding of the considerations that motivated the idea of the sea of
radiation.Comment: A 24-page preprint; version 2 has additions, revisions and
corrections to version
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