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

F

2MASS 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 the

Cosmological 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 + - 1 Curvature Matter Dark (Vacuum)

Energy

Matter and Dark Energy tell space how to

curve:

k = m + - 1 Curvature 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 = 0.7

k = 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 distance

Growth rate of structure

Evolution of dark matter perturbations

Standard ruler

Angular diameter distance

Standard candle

Luminosity distance

Evolution of dark matter perturbations

Angular diameter distance

Growth rate of structure

Snapshot of Universe at ~400,000 yr

Angular diameter distance to z~1000

Growth 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

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 al

Astro-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

WDM CDM+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

SKA FMOS KAOS

SDSS

Imaging CFHTLS

ATLAS KIDS

DES

VISTA JDEM/

SNAP

LSST SKA

Pan-STARRS

SDSS

SUBARU

Surveys to measure Dark Energy

2005

2015 2005 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 galaxies

over 1/8 of the sky

2009-2014

Multiple Techniques:

-Galaxy clustering

-Clusters

-Supernovae Ia

-Weak Gravitational lensing

Measure W to a few percent Galactic Dust Map

Dark Energy Survey Instrument

3.5 meters

Camera

Filters

Optical Lenses

Scroll

Shutter

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=300

WL: lmax=1000

(no bispectrum)

Statistical+photo-z

systematic errors only

Spatial curvature, galaxy bias

marginalized

Planck CMB prior

w(z) =w0+wa(1–a) 68% CL

geometric

geometric+

growth

Clusters

if 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?