Towards Cosmography of the Local Universe
arxiv(2024)
摘要
Anisotropies in the distance-redshift relation of cosmological sources are
expected due to large-scale inhomogeneities in the local Universe. When the
observed sources are tracing a large-scale matter flow in a general spacetime
geometry, the distance-redshift relation with its anisotropies can be described
with a geometrical prediction that generalises the well-known
Friedmann-Lemaître-Robertson-Walker result. Furthermore, it turns out that a
finite set of multipole coefficients contain the full information about a
finite-order truncation of the distance-redshift relation of a given observer.
The multipoles of the distance-redshift relation are interesting new
cosmological observables that have a direct physical interpretation in terms of
kinematical quantities of the underlying matter flow. Using light cones
extracted from N-body simulations we quantify the anisotropies expected in a
Λ cold dark matter cosmology by running a Markov chain Monte Carlo
analysis on the observed data. In this observational approach the survey
selection implements an implicit smoothing scale over which the effective rest
frame of matter is fitted. The perceived anisotropy therefore depends
significantly on the redshift range and distribution of sources. We find that
the multipoles of the expansion rate, as well as the observer's velocity with
respect to the large-scale matter flow, can be determined robustly with our
approach.
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