Introduction to Cosmology Ofer Lahav University College London The zoo of cosmological parameters...
-
Upload
christopher-dorsey -
Category
Documents
-
view
225 -
download
4
Transcript of Introduction to Cosmology Ofer Lahav University College London The zoo of cosmological parameters...
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?