Measuring dark energy from galaxy surveys
Carlton BaughDurham University
London 21st March 2012
Galaxies to cosmological parameters
Connecting dark matter to linear theory
Linear perturbation theory Evolved matter distribution: MXXL
Angulo et al. 2012
Connecting galaxies to mass
H-a H-band
Orsi et al. 2010
A hybrid tool to study dark energy
N-body simulation Galaxy formation simulation
Bias and nonlinear
effects
Angulo et al. 2008
Scale dependent biases
Linear theory
Dark matter
Angulo et al. 2008
Scale dependent RSD
Jennings et al. 2011
Linear theory
Scale dependent RSD
Jennings et al. 2011
The need for improved RSD models
Jennings et al. 2011
Using linear theory leads to systematic errors similar to difference in signal
Measuring DE using galaxy pairsPeculiar motions distort apparent distribution of pair angles:
Jennings et al. 2012
Marinoni & Buzzi 2010
A probe of dark energy
• Peculiar velocities give distortion in pair angle distribution
• Probe of Hubble expansion• Distortion sensitive to nature
of dark energy• Distinguish models with same
BAO and halo mass function• Requires simulations
Jennings et al. 2012
Why build a mock catalogue?
A synthetic galaxy can catalogue be used to: • Test estimators: e.g. Galaxy clustering, photo-z,
group-finders• Devise new statistics: e.g. pair distortions• Uncover systematic effects (we already know the
right answer)• Estimate errors• Generate predictions for different dark energy
cosmologies
What is a mock catalogue?
N-body simulation Combine with galaxy formation model
Millennium, Horizon, MICE, MXXL e.g. GALFORM; GALICS, LGALAXIES; MORGANASpringel et al. 2005, Teyssier et al. 2009;Fosalba et al 2008; Angulo et al. 2012 Cole et al. ;Hatton etal; de Lucia et al; Monaco +
A priori calculation of baryon physics
STEP 1 STEP 2
Build galaxy catalogue on observer’s past lightcone.
Constructing observer’s past lightcone
redshift
STEP 3
e.g. Blaizot et al 2005; Fosalba et al.Kitzbichler & White; Merson et al.
Apply survey “window function”
• Apply angular footprint• Apply scanning mask• Incorporate sampling• Redshift completeness
(synergy with OU-SIM)• Steps 1, 2, 3 generic• Step 4 is survey specific
Synthetic images
Merson et al. 2012
Merson et al. 2012
Merson et al. 2012
Summary
• Hybrid tool: N-body and galaxy formation sims• Linear theory not accurate enough for Euclid
on large-scales• Scale dependent: nonlinearities, bias, RSD• Mock catalogues will help refine estimators• Devise new tests
Recommended
