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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
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
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
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
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)
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
Sources of uncertainties
• Cosmological (parameters and priors)
• Astrophysical (e.g. cluster M-T, biasing)
• Instrumental (e.g. “seeing”)
Wiener Reconstruction of density
and velocity fields from
the 2MASS Redshift Survey
Erdogdu, Lahav, Huchra et al
Astro-ph/0610005
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