Dark Energy: Observations Gil Holder Outline How dark energy - - PowerPoint PPT Presentation

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Dark Energy: Observations Gil Holder Outline How dark energy - - PowerPoint PPT Presentation

May 31, 2023 506 likes •967 views

Dark Energy: Observations Gil Holder Outline How dark energy affects cosmological observables a(t) => distances(z), growth of structure(z) Dark energy probes cosmic microwave background supernovae (type IA) galaxy

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Dark Energy: Observations

Gil Holder

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Outline

  • How dark energy affects cosmological
  • bservables
  • a(t) => distances(z), growth of structure(z)
  • Dark energy probes
  • cosmic microwave background
  • supernovae (type IA)
  • galaxy clustering
  • weak gravitational lensing
  • galaxy cluster number counts

Warning: not a comprehensive list of experiments!

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+cmb

supernovae galaxy clustering

Sullivan et al 2011

w=-1.06 +-0.07

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Energy Densities in Cosmology

d(ln a)/dt matter dark energy

a=1/(1+z)

scale factor

redshift

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The expanding universe

  • spatially flat FRW: dt2=a2(t) dr2
  • mapping between comoving distance

between points and time depends on expansion history

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Dark Energy from Distances

  • distance

sensitive to expansion rate

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Gravity at work

simulations carried out by the Virgo Supercomputing Consortium using computers based at Computing Centre of the Max-Planck Society in Garching and at the Edinburgh Parallel Computing Centre. The data are publicly available at www.mpa-garching.mpg.de/NumCos

t=400 000 yrs t=20 million yrs t=500 million yrs t=13.7 billion yrs

simulated density contrast at different times

1 billion light years

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  • Growth of

structure sensitive to expansion rate

Amplitude of density fluctuations in linear theory:

Amplitude of linear density fluctuations

w=-1/3

Λ

Dark Energy Studies with Growth Tests

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! !!! !

  • Fig. VI-2: The primary observables for dark-energy – the distance-redshift relation DDz)!
  • Characterizing

Dark Energy

from Dark Energy Task Force report

w=-0.9 w=-1

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Cosmic Microwave Background

  • acoustic scale (in cm)

set by physics unrelated to dark energy

–angular scale depends

  • n expansion history
  • provides

normalization of fluctuation amplitude at z~1100

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WMAP (all sky)

South Pole Telescope (total 2500 sq deg)

8o

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CMB Power Spectrum

SPT power spectra: Ryan Keisler; Christian Reichardt; Erik Shirokoff

characteristic spacing set by angular size of sound horizon at z=1089

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! !!! !

  • Fig. VI-2: The primary observables for dark-energy – the distance-redshift relation DDz)!
  • Characterizing

Dark Energy

from Dark Energy Task Force report CMB

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Exploding stars: Supernovae

nearby (Type II) distant (Type IA) It appears that some supernovae (IA) all have the same intrinsic brightness

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Supernova!

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SNe Multi-color Light Curves

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Conley et al 2008

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Standardized Candles

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each panel is a different wavelength range

Conley et al 2008

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SNe Hubble Diagram

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14 16 18 20 22 24 26 mcorr = mB + ! (s − 1) − " C

Low−z SDSS SNLS HST

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 z

−0.6 −0.4 −0.2 0.0 0.2 0.4 0.6 mcorr

5 l

  • g

1

( d i s t a n c e )

Conley et al 2011

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Forecast & Wish List for SNe

  • need more SNe both at low-z and at z>1

–population studies to ensure that there isn’t some evolution in either each SN or in the demographics of the SN population

  • more colors would be nice (IR, UV?)

–space-based? (WFIRST)

  • a strong theoretical understanding of

spectra & light curves would be reassuring

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! !!! !

  • Fig. VI-2: The primary observables for dark-energy – the distance-redshift relation DDz)!
  • Characterizing

Dark Energy

from Dark Energy Task Force report CMB

SNe

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BAO

  • Baryon

Acoustic Oscillations leave imprint in matter distribution

Eisenstein, Seo & White 2006

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Galaxy Clustering

  • galaxies are

clustered

  • amplitude a bit tricky

to use because galaxies live at peaks

  • f density field

(``biased’’)

  • BAO signature

leads to boosted clustering on acoustic scale (~100 h-1Mpc) slice through SDSS survey

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Baryon Oscillations imprinted in Galaxy Clustering

  • first detected in

Eisenstein et al 2005 using SDSS LRG sample (extends to z~0.5)

  • actually detected

in angular & radial clustering

  • standard

ruler

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The BAO Hubble Diagram

  • BAO

measurements at different z allow a test of the distance- redshift relation

Blake et al 2011

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The BAO Hubble Diagram

  • BAO

measurements at different z allow a test of the distance- redshift relation

Blake et al 2011

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Forecast & Wish List for BAO

  • minimal (but not completely negligible) non-

linear physics

  • mainly need more volume
  • 100 Mpc/h scale + 1% precision requires at least

a few Gpc on a side surveys (cH0-1~3 Gpc/h)

  • lots of ideas & new surveys
  • e.g.., quasar absorption lines/optical galaxies

(BigBoss); CHIME (21cm intensity mapping)

just my personal favorites, no offense to the many others...

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! !!! !

  • Fig. VI-2: The primary observables for dark-energy – the distance-redshift relation DDz)!
  • Characterizing

Dark Energy

from Dark Energy Task Force report CMB

SNe BAO

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Gravitational Lensing

  • Distortion, multiple

imaging of distant sources

http://imagine.gsfc.nasa.gov/docs/features/news/grav_lens.html

www.hubblesite.org

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Gravitational Lensing

  • Distortion, multiple

imaging of distant sources

  • amount of lensing

depends on source/ lens/observer geometry (distances)

http://imagine.gsfc.nasa.gov/docs/features/news/grav_lens.html

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Weak Lensing

  • gravitational potentials

distort shapes by stretching, squeezing, shearing

  • typical cosmic shear

signal ~1%

Gravity

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Galaxies are not round

  • individual galaxies have

complex morphologies

  • solution: average over

many galaxies

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Cosmic Shear Measurements

  • very strong

detections are now being made

  • e.g., CFHTLS has

published results from 57 sq deg of single-band ground- based imaging

$ [arcmin]

  • 2.0!10-5

0.0!100 2.0!10-5 4.0!10-5 6.0!10-5 8.0!10-5 1.0!10-4 1.2!10-4 1.4!10-4 1 10 100

<|%|2> $ [arcmin]

  • 5.0!10-6

0.0!100 5.0!10-6 1.0!10-5 1.5!10-5 50 100 150 200 250

CFHTLS

Fu et al 2008

(error bars are correlated)

shear variance in top hat window

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Weak lensing tomography

  • using source galaxies at

different redshifts allows

  • ne to reconstruct the 3D

mass distribution

  • mass, not galaxy, density

means you can measure the time evolution of the density fluctuations

  • recent results using Hubble
  • ver ~1 sq deg

Massey et al

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Weak lensing tomography

  • using source galaxies at

different redshifts allows

  • ne to reconstruct the

3D mass distribution

  • mass, not galaxy, density

means you can measure the time evolution of the density fluctuations Schrabback et al 2010

0.2 0.4 0.6 0.8 1.0 −2.0 −1.5 −1.0 −0.5 0.0

!m w

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  • CMB is a unique source for lensing
  • Gaussian, with well-understood

power spectrum (contains all info)

  • At redshift which is (a) unique,

(b) known, and (c) highest

T L(ˆ n) = T U(ˆ n + ∇φ(ˆ n))

CMB Lensing

Broad kernel, peaks at z ~ 2

Photons get shifted

ˆ n

T

ˆ n + ∇φ

strong detections now exist

Power spectrum of density fluctuations

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Forecast & Wish List for lensing

  • cosmic shear requires large areas, good redshift

discrimination, good telescope understanding

  • space-based may be easier (high resolution, broad

wavelength coverage, very dark sky)

  • large surveys coming soon: 1000s of square

degrees of deep imaging (DES, Pan- Starrs, ...,LSST)

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! !!! !

  • Fig. VI-2: The primary observables for dark-energy – the distance-redshift relation DDz)!
  • Characterizing

Dark Energy

from Dark Energy Task Force report CMB

SNe BAO

Lensing

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Number counts of rare objects

  • simulated 2x2 degree

map showing projected thermal pressure

  • number of most

massive objects highly sensitive to amplitude

  • f density fluctuations
  • 10%

ref fluctuation amplitude

+10%

+20%

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Image by Will High in recent paper by Williamson et al

One of the heaviest objects in the universe >1015 solar masses

patch of isolated cosmic fog

CMB map made with South Pole Telescope

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Cluster dN/dz

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Vanderlinde et al 2010

First SPT Cosmological result (Vanderlinde et al 2010), used SPT’s first 21 clusters to constrain cosmology 100 steps from WMAP7 wCDM MCMC chain with SPT dN/dz overplotted

slide from Brad Benson

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Constraints on dark energy from X-ray selected galaxy clusters

  • Vikhlinin et al 2009

(see also Mantz et al)

  • ~60 clusters at z<0.7
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Forecast & Wish List for galaxy clusters

  • need larger samples: 1% requires 1000s of

clusters just to beat Poisson noise: eROSITA (X- ray), DES (optical)

  • need strong validation campaign to ensure the

sample properties are well-understood (i.e., make sure that the number of objects is changing, not the type of object that is being found)

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! !!! !

  • Fig. VI-2: The primary observables for dark-energy – the distance-redshift relation DDz)!
  • Characterizing

Dark Energy

from Dark Energy Task Force report CMB

SNe BAO

Lensing Clusters

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Summary

  • dark energy is being observed in many

different ways

  • first discovered through supernovae, but many independent

cross-checks!

  • distances & structure formation are two

fundamentally different tests

  • all methods have strengths and weaknesses

but great promise for figuring out dark energy