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Systematic variations of the Hubble flow
EWASS 2015 talkSpecial Session 2
June 22, 2015
by
Christoph Saulder(University of Vienna)
in collaboration withSteffen Mieske (ESO Chile), Eelco van Kampen (ESO Garching), and Werner Zeilinger (University of Vienna)
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Why do we need Dark Energy?● Mainly to explain the accelerated expansion
of the universe (distant supernovae type Ia – Nobel prize 2011)
What is Dark Energy?● We do not know!!!
– Simplest assumption: cosmological constant – Phantom dark energy or quintessence
– Many other models without any proof
● But it fits our data well, if we assume isotropy and homogeneity (FLRW-metric).
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Timescape Cosmology● cosmological model based on the assumption that
the universe is NOT homogeneous at all scales
==> voids and clusters+filaments (walls)by MPA
by 2dFGRS
by 2dFGRS
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● General Relativity is a non-linear theory (FACT).● At last scattering the universe was very close to
homogeneity (FACT).● Today the matter distribution in the universe has
void-dominated fractal bubble structure (FACT).
● ==> averaging over large scale and high density contrast has to be modified.
● Back-reactions from inhomogeneities expected● Wiltshire, 2007 model: dropping the cosmological
time parameter and assuming a two phase model (voids and walls) with a fractal bubble structure.
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Consequences of this theory
● Voids expand faster than walls ● Structure formation made the universe
inhomogeneous and caused the apparent accelerated expansion.
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Consequences of this theory
● Voids expand faster than walls ● Structure formation made the universe
inhomogeneous and caused the apparent accelerated expansion.
● Thereby, one naturally gets an
accelerated expansionwithout the need for
Dark Energy!
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Testing the theory● Idea: Search for systematic variations of the
Hubble flow depending on the structure in the line of sight, because voids expand faster than walls in timescape cosmology.
● We need: ● A redshift independent distance indicator:
fundamental plane of elliptical galaxies
with calibrations of Saulder+2013
& updated values from Saulder+2015a
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● Large sample distributed over a large area of the sky to avoid biases and get good statistics.
==> SDSS DR10 + 2MRS
● A complete model of matter distribution in the local universe: Saulder+2015b, submitted
● Simulated data for both theories to estimate potential biases and compare the observations to
==> wide angle mock catalogues based on the Millennium simulation: Saulder+2015b, submitted & Saulder+2015c, in prep.
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The semi-final results
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Conclusions & Summary● We managed to perform a meaningful test for
timescape cosmology against the standard model with public survey data and simulated data only.
● Surprising diversity of our observational parameters between the different mock catalogues for the same cosmological model.
● Final results in preparation (Saulder+2015c, in prep.)
● Statistical analysis is still work in progress (least squares, binning, KS-test, etc.)
● So far, the data seems to favour -CDM, but its significance depends on the analysis method.
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ANY QUESTIONS?
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Supplementary slides
Only for Q&A … if asked for.
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CDM bias due to coherent infall
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Finite infinity regions
● Approximated by (overlapping) spherical regions with an average density equal to the renormalized critical density in timescape cosmology.
by Wiltshire 2007
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Variations between the different mock catalogues
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Full data, binned
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Full data, least squares
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Mock catalogues, -CDM
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Mock catalogues, timescape
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N/A
Sorry,
but I haven't prepared a slide for this question.