Introduction to Cosmology

Ofer Lahav University College London

• The zoo of cosmological parameters

• Dark Matter and Dark Energy surveys

UCL Astrophysics http://www.star.ucl.ac.uk

Approximately 20 academic staff, 15 post-docs, 40 PhDs, 15 support staff

• Research Areas: Stellar astrophysics, Star formation, Astro-chemistry, Cosmology,Atmospheric Physics, Astro-biology, Instrumentation, Mill Hill Observatory & the MSSL Department

UCL founded 1826

18th Cumberland Lodge meeting July 2005

“Nearly Normal Galaxies” conference

Santa Cruz 1986

cf. Cosmology in 1986

“Standard Cold Dark Matter”

m = 1, =0

H0 = 50 km/sec/Mpc = 1/(19.6 Gyr)

Galaxy redshift surveys of thousands of galaxies (CfA1, SSRS, ORS, IRAS)

Peculiar velocities popular (7S) CMB fluctuations not detected yet

FF

2MASS Galactic chart2MASS Galactic chart

Evidence for Dark Energy

Supernovae as standard candles

CMB – a flat universe LSS - low m

Clusters - low m

Baryon Wiggles as standard rulers

Integrated Sachs Wolfe

Geometry vs. Growth of structure

Multiple approaches are essential!

The Chequered History of theCosmological Constant

The old CC problem:Theory exceeds observational limits on by 10120 !

The new CC problem:Why are the amounts of Dark Matter and Dark Energy so similar?

Matter and Dark Energy tell space how to curve:

k = m + - 1Curvature Matter Dark (Vacuum) Energy

Matter and Dark Energy tell space how to curve:

k = m + - 1Curvature Matter Dark (Vacuum) Energy

k - = m - 1

OR modified curvature

The Universe accelerates at present if

m/2 - < 0

e.g. For m = 0.3 and = 0.7k = 0 (the U. is flat!) and the U. is accelerating! (only ‘recently’, z<0.7)

Just Six numbers (?) Baryons b

Matter m

Dark Energy (Cosmological Constant)

Hubble parameter H0

Amplitude A Initial shape of perturbations (n = 1 ?)

Through the history of the expansion rate:

H2(z) = H20 [M (1+z) 3 + DE (1+z) 3 (1+w) ] (flat Universe)

matter dark energy (constant w) P = w

Comoving distance r(z) = dz/H(z) Standard Candles dL(z) = (1+z) r(z) Standard Rulers dA(z) = (1+z)1 r(z)

The rate of growth of structure also determined by H(z) and by any modifications of gravity on large scales

Probing Dark Matter & Dark Energy

Curvature of the Universe bends light

CMB

Cluster counts

Supernovae

Baryon Wiggles

Cosmic Shear

Probes of Dark Matter and Dark Energy

Angular diameter distanceGrowth rate of structure

Evolution of dark matter perturbations

Standard rulerAngular diameter distance

Standard candleLuminosity distance

Evolution of dark matter perturbationsAngular diameter distanceGrowth rate of structure

Snapshot of Universe at ~400,000 yrAngular diameter distance to z~1000Growth rate of structure (from ISW)

Supernovae

• Geometric Probe of Dark Energy

SDSS

The History of CMB observations

1965

1992

2003

Discovery

COBE

WMAP

WMAP3

m = 0.24 +-0.04 8 = 0.74 +-0.06 n = 0.95 +-0.02 = 0.09 +-0.03

Observer

Dark matter halos

Background sources

Statistical measure of shear pattern, ~1% distortion Radial distances depend on geometry of Universe Foreground mass distribution depends on growth of structure

Weak Lensing: Cosmic Shear

A. Taylor

Recent w from the CTIO

Jarvis & Jain, astro-ph/0502243

W=-0.894+0.156 -0.208

Linder 05

W = P/

W = W0 + (1-a) Wa

Sources of uncertainties

• Cosmological (parameters and priors)

• Astrophysical (e.g. cluster M-T, biasing)

• Instrumental (e.g. “seeing”)

Redshift Surveys

Wiener Reconstruction of density and velocity fields from

the 2MASS Redshift Survey

Erdogdu, Lahav, Huchra et alAstro-ph/0610005

The evolution of the Cosmic Web

in the past 20 years

CfA Great Wall

SDSS

Great Attractor 2dFGRS

From 2dF+CMB (6 parameter fit): m=0.23 §0.02

Cole et al. 2005

Brief History of ‘Hot Dark Matter’

* 1970s : Top-down scenario with massive neutrinos (HDM) – Zeldovich Pancakes

* 1980s: HDM - Problems with structure formation

* 1990s: Mixed CDM (80%) + HDM (20% )

* 2000s: Baryons (4%) + CDM (26%) +Lambda (70%): But now we know HDM exists! How much?

Neutrinos decoupled when they were still relativistic,hence they wiped out structure on small scales

112 neutrinos per cm3

WDMCDM+HDM

CDM

From 2dF < 0.04 ; M < 1.8 eV (Elgaroy & OL 2003)From Ly-a+SDSS +CMB M < 0.17 eV (Seljak et al. 2006)

2015

CMB WMAP 2/3 WMAP 6 yr

Planck Planck 4yr

Clusters AMI

SZA

APEX

AMIBA

SPT

ACT

DES

Supernovae

Pan-STARRS

DES LSST

JDEM/SNAP

CFHTLS

CSP

Spectroscopy

ATLAS

SKAFMOS KAOS

SDSS

Imaging CFHTLS

ATLAS KIDS

DES

VISTA JDEM/SNAP

LSST SKA

Pan-STARRSSDSS

SUBARU

Surveys to measure Dark Energy

2005

20152005 2010

2010

Dark Energy Task Force Recommendations

• An immediate start of a near-term program (which we call Stage III) designed to advance our knowledge of dark energy and prepare for the ultimate “Stage IV” program, which consists of a combination of large survey telescopes and/or a space mission.

Advocate Fisher Matrices!

The Dark Energy Survey

• 4 complementary techniques:

* Cluster counts & clustering * Weak lensing * Galaxy angular clustering * SNe Ia distances

Build new 3 deg2 camera on the CTIO Blanco 4m Construction 2005-2009 Survey 2009-2014 (~525 nights)

5000 deg2 g, r, i, z 300, 000, 000 galaxies with photo-z

Cost: $20M

The Dark Energy Survey

300,000,000 galaxiesover 1/8 of the sky

2009-2014

Multiple Techniques:-Galaxy clustering-Clusters-Supernovae Ia-Weak Gravitational lensing

Measure W to a few percentGalactic Dust Map

Dark Energy Survey Instrument

3.5 meters

Camera

Filters

Optical Lenses

ScrollShutter

1.5 meters

New Prime Focus Cage, Camera, and Corrector for the Blanco 4m Telescope 500 Megapixels, 0.27”/pixel Project cost: ~20M$ (incl. labor)

P5 – April 20, 2006

DES Forecasts: Power of Multiple Techniques

Frieman, Ma, Weller, Tang, Huterer, etal

Assumptions:Clusters: 8=0.75, zmax=1.5,WL mass calibration(no clustering)

BAO: lmax=300WL: lmax=1000(no bispectrum)

Statistical+photo-z systematic errors only

Spatial curvature, galaxy biasmarginalized

Planck CMB prior

w(z) =w0+wa(1–a) 68% CL

geometric

geometric+growth

Clustersif 8=0.9

DUNE: Dark UNiverse Explorer

Mission baseline: • 1.2m telescope • FOV 0.5 deg2

• PSF FWHM 0.23’’• Pixels 0.11’’ • GEO (or HEO) orbit

Surveys (3-year initial programme):• WL survey: 20,000 deg2 in 1 red broad band, 35 galaxies/amin2 with median z ~ 1, ground based complement for photo-z’s

• Near-IR survey (J,H). Deeper than possible from ground. Secures z > 1 photo-z’s

• SNe survey: 2£60 deg2, observed for 9 months each every 4 days in 6 bands, 10000 SNe out to z ~ 1.5, ground based spectroscopy

Baryon Wiggles as Standard Rulers

What is the Dark Energy?

* Vacuum energy (cosmological constant) * Dynamical scalar field * Manifestation of modified gravity

If w= -1.000 then what?

New Physics? The Anthropic Principle? Multiverse?