Measuring dark energy from galaxy surveys

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