Measuring dark energy from galaxy surveys Carlton Baugh
Measuring dark energy from galaxy surveys Carlton Baugh Durham University London 21 st 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 Dark matter Linear theory Angulo et al. 2008
Scale dependent RSD Linear theory Jennings et al. 2011
Scale dependent RSD Jennings et al. 2011
The need for improved RSD models Using linear theory leads to systematic errors similar to difference in signal Jennings et al. 2011
Measuring DE using galaxy pairs Marinoni & Buzzi 2010 Peculiar motions distort apparent distribution of pair angles: Jennings et al. 2012
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? STEP 1 STEP 2 N-body simulation Combine with galaxy formation model A priori calculation of baryon physics Millennium, Horizon, MICE, MXXL Springel et al. 2005, Teyssier et al. 2009; Fosalba et al 2008; Angulo et al. 2012 e. g. GALFORM; GALICS, LGALAXIES; MORGANA Cole et al. ; Hatton etal; de Lucia et al; Monaco +
Constructing observer’s past lightcone STEP 3 red shi ft Build galaxy catalogue on observer’s past lightcone. 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
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