Superno vae - standar d candles · Superno vae - standar d candles. Superno vae - standar d candles...

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What is Dark Energy? Chris Blake (Swinburne) What are the big questions today in cosmology? How can large galaxy surveys help us to address these questions? The WiggleZ survey : measuring cosmic sound waves The history of the Universe! The main probes of cosmology Supernovae Large-scale structure Cosmic Microwave Background Supernovae - standard candles Known luminosity Supernovae - standard candles

Transcript of Superno vae - standar d candles · Superno vae - standar d candles. Superno vae - standar d candles...

Page 1: Superno vae - standar d candles · Superno vae - standar d candles. Superno vae - standar d candles Redshift Superno va of dimmer magnitude With dark energ y Dark matter onl y Low-density

What is Dark Energy?

Chris Blake (Swinburne)

• What are the big questions today in cosmology?

• How can large galaxy surveys help us to address these questions?

• The WiggleZ survey : measuring cosmic sound waves

The history of the Universe! The main probes of cosmology

Supernovae Large-scale structure

Cosmic Microwave Background

Supernovae - standard candles

Knownluminosity

Supernovae - standard candles

Page 2: Superno vae - standar d candles · Superno vae - standar d candles. Superno vae - standar d candles Redshift Superno va of dimmer magnitude With dark energ y Dark matter onl y Low-density

Supernovae - standard candles

Redshift

Super

nova

of dim

mer

mag

nitude

With dark energy

Dark matter only

Low-density model

The accelerating expansion

Large-scale structure of the Universe

2-degree Field Galaxy Redshift Survey

Fluctuations in the Cosmic Microwave Background

Theoretical simulations

Redshift z=1 Redshift z=3

What is the composition of the Universe?

No Big Bang

1 2 0 1 2 3

expands forever

-1

0

1

2

3

2

3

closed

recollapses eventually

Supernovae

CMB

Clusters

open

flat

Knop et al. (2003)Spergel et al. (2003)Allen et al. (2002)

Supernova Cosmology Project

Ω

ΩΛ

MAmount of dark matter

Am

ount

of dar

k en

ergy

Concordance cosmology

Page 3: Superno vae - standar d candles · Superno vae - standar d candles. Superno vae - standar d candles Redshift Superno va of dimmer magnitude With dark energ y Dark matter onl y Low-density

What is the composition of the Universe? Einstein’s cosmological constant

• Cosmological constant is profoundly inconsistent with quantum mechanics

• We must either change the laws of gravity or explain a “substance” that comprises the bulk of the universe

• Alternative models (quintessence) predict properties of dark energy should evolve with redshift

• Current observations cannot discriminate between these models

The problem of dark energy Fate of the Universe

Cosmic sound waves

Temperature cooling ...

Last scattering / recombination

Cosmic sound wavesSeeing Sound

The most prominent and useful features in the anisotropy of the CMB come from acoustic oscillations of thephoton-baryon fluid. Radiation pressure from the photons resists the gravitational compression of the fluidinto potential wells and sets up acoustic oscillations in the fluid:

Figure:Radiation Pressure and Gravity

Springs represent photon pressure and balls represent the effective mass of the fluid.

The shorter the wavelength of the potential fluctuation the faster the fluid oscillates such that at lastscattering the phase of the oscillation reached scales with the wavelength. Since regions of compression(maxima) represent hot regions and rarefaction (minima) cold regions, there will be a harmonic series ofpeaks in wavelength associated with the acoustic oscillations. It is the features of these peaks that provide uswith an array of cosmological tests.

Figure:Acoustic Oscillations

Displayed here is the time evolution of a single wavelength of the potential fluctuation (Fourier amplitudetime evolution on right).

Technical note: Since the photons must climb out of the potential wells at last scattering, the effectivetemperature, Theta+Psi, is reduced at long wavelengths to 1/3 Psi. This effect is commonly known as theSachs-Wolfe effect.

Dark matter clump containing baryons and radiation

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Cosmic sound waves

150 Mpc

Forming galaxies

= distance travelled by sound wave before recombination

Cosmic sound waves

Num

ber

of pai

rs o

f ga

laxie

s

Separation of galaxies (Mpc / h)

Result from the Sloan Digital Sky Survey of local galaxies:

Signature of cosmic sound wave

Cosmic sound waves

Standard candle Standard ruler

Supernova Cosmic sound wave

The WiggleZ survey

Collaboration led by Swinburne and U.Q.

The WiggleZ survey

Survey mission : obtain redshifts of 200,000 high-redshift galaxies (0.5 < z < 1.0) over 1000 sq degs

Science goal : first detection of cosmic sound waves at high redshift and a robust test of dark energy

The WiggleZ survey

NUV FUV

AA! spectrum

[OII] H"

Example target : high-redshift star-forming galaxies

Page 5: Superno vae - standar d candles · Superno vae - standar d candles. Superno vae - standar d candles Redshift Superno va of dimmer magnitude With dark energ y Dark matter onl y Low-density

The WiggleZ survey

Survey progress : 50 nights so far out of 220

The WiggleZ survey

• What is the mass of the neutrino ?

Cold

Warm

Hot

The WiggleZ survey

• Measuring the physics of inflation • Dark energy is a fundamental problem

• Galaxy surveys can measure dark energy by mapping the imprint of cosmic sound waves

• WiggleZ survey will provide first high redshift application of this technique

To sum up ...

Chris Blake - room AS403 - [email protected]