elise jennings - bccpbccp.berkeley.edu/beach_program/presentations12/jennings.pdf · - model...
TRANSCRIPT
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Elise Jennings University of Chicago
THE ENRICO FERMI INSTITUTE
THE UNIVERSITY OF CHICAGO
Cosmology on the beach - Cancun 2012
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•Redshift space distortions
• The Alcock-Paczynski effect
• Testing dark energy using pairs of galaxies
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Large volume N-body simulations: an essential tool
- Model nonlinear fluctuation growth, peculiar
motions, nonlinear and scale dependent bias - How well can we constrain w(z) using BAO?
(see Angulo et al. 2008)
- Accuracy in measuring growth rate f
1. Expansion history to better than 1%
2. Growth rate of structures to ~2%
e.g. BOSS, WiggleZ, EUCLID,WFIRST, BigBOSS, LSST, etc...
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Peculiar velocities affect the inferred
distance to an object
Kaiser (1987)
Hamilton (1997)
true
distance
peculiar
velocity
redshift
distance
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Assuming a FRW metric - a spherical object uniformly
expanding in all directions
Using the correct cosmological model to estimate distances etc
But redshift space distortions lead to radial anisotropies which
we need to model...
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t
Real space
Assuming homogeneity & isotropy &
flat Universe
Expect the separation vector to be
randomly orientated
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t
Redshift space
Apparent angle of inclination
Distant observer approximation
Conservation of probability
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•How robust is the
selection criterion?
•Is the
normalisation
independent of z?
•How well does
this test work in
different
cosmologies?
PIC FROM MB
2011
Marinoni & Buzzi 2011
Normalisation parameter α
depends on selected pairs
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EJ, CMB & SP
2010
SUGRA
INV
LCDM & quintessence dark energy N-body simulations Modify N-body code : L-Gadget 2 (Springel 2005)
Np = 10243 ~ 1 x 109 particles
Lbox = 1500 h-1 Mpc
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Measurements
of the
distribution in
LCDM at z=0
Selection effects
very important as
including outliers
randomizes the
distribution
Subhalo pairs
identified at
various redshifts
with dr < R200 and
a limit on dV
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EJ, CMB & SP 2011
Measurements
the first moment
of the
distribution
LCDM prediction
using normalisation
measured from
simulation
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EJ, CMB & SP 2011
INV cosmology
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EJ, CMB & SP 2011
INV cosmology
SUGRA cosmology
Key assumptions
•Correct
normalisation for
distribution
•Correct
cosmological model
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EJ, CMB & SP 2011
When it is LCDM...assuming a LCDM
cosmology and fitting for the
normalisation seems to work...
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Assuming LCDM
and fitting for the
normalisation
does not work...
when correct
model is not
LCDM !
Theory &
observation should
not agree as we
have assumed the
wrong
cosmological
model!
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EJ, CMB & SP 2011
Measured assuming
LCDM cosmology
Prediction from
a LCDM simulation
•Assume a cosmology to
find distances to galaxies
•Run an N-body sim in
the same cosmology with
same number density &
volume as the survey
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• Anisotropy of pairs of galaxies looks like a promising
probe of Dark Energy – distinguish LCDM and
quintessence models that have identical BAO and mass
functions
• Alternative use of the AP effect in addition to BAO
measurements.