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8/3/2019 Scott Croom- Dark energy and cosmic sound
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Dark energy andcosmic sound
1. The evidence for dark energy.2. Acoustic waves as standard rulers.
3. The WiggleZ Survey.
Scott Croom
(Sydney Institute for Astronomy)
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The fate of the UniverseThe Universe: dark matter
baryons
neutrinos
photons
m>1 m=1 m
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Standard Candles
If we know the intrinsic brightness of anobject we can calculate its distance:
But distance (r) depends on redshift (i.e.
cosmological expansion) and the content ofthe Universe.
Supernovae (in particular type Ia SNe) are
good standard candles.
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Type Ia SNe
Thermo-nucleardetonation of a whitedwarf.
Can outshine theirgalaxy.
Their peak luminosity
is consistent to ~10%.
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An unexpected result
AcceleratingCoasting
Critical
-2.5
log10
(measuredre
lativeSNflux)
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The fate of the Universe
X X X
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Dark Energy whats going on?
One of Key Science Questions for the NewCentury (US National Academies, 2003)
Cosmic acceleration requires new physics:
Cosmological constant: natural scale very wrong (z=0) / Planck = H0
2 h G c5 = 10-122
New theory of gravity?
Quintessence/phantom energy?
Connection to inflation?
Extra dimensions?
New particle interactions?
Dark-matter dark-energy connections?
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The physics of dark energy
The equation of state: w=p/ Normal matter w=0, V-1
Photons w=1/3, V-4/3
Friedmann equations give: Acceleration -(1+3w) w accelerating Universe
Dark Energy:
Cosmological constant: w=-1, V0 Quintessence: w(z)=-1/3 to -1 Phantom energy: w
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Vacuum energy
The cost of space?
Work done = -pdV
Vacuum energy: dE = dV
So dV = -pdV
And w=p/=-1
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Tracker Quintessence, single exp Quintessence, double expQuintessence, Pseudo-Nambu-Goldstone Boson Quintessence,Holographic dark energy, cosmic strings, cosmic domain walls, axion-photon coupling, phantom dark energy, Cardassian model, branecosmology (extra-dimensions), Van Der Waals Quintessence, Dilaton,
Generalized Chaplygin Gas, Quintessential inflation, Unified Darkmatter & Dark energy, superhorizon perturbations, UndulantUniverse, various numerology, Quiessence, general oscillatory models,Milne-Born-Infeld model, k-essence, chameleon, k-chameleon, f(R)gravity, perfect fluid dark energy, adiabatic matter creation, varyingG etc, scalar-tensor gravity, double scalar field, scalar+spinor,Quintom model, SO(1,1) scalar field, five-dimensional Ricci flatBouncing cosmology, scaling dark energy, radion, DGP gravity, Gauss-Bonnet gravity, tachyons, power-law expansion, Phantom k-essence,vector dark energy, Dilatonic ghost condensate dark energy,Quintessential Maldacena-Maoz dark energy, superquintessence,
vacuum-driven metamorphosis, wet dark fluid...
Dark Energy whats going on?
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Issues with SN
Evolution of progenitors?
Host galaxy environments?
Dust? Explosions not understood.
Calibration: Now limited at >1%
Need something else a standard ruler?
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A standard ruler: Cosmic sound
aka: Baryon acoustic oscillations (BAOs)
Baryon wiggles Doppler peaks
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Measuring cosmic sound (1)CMB from WMAP (z=1500)
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Measuring cosmic sound (2)
Galaxy redshift surveys can measurethe 3-D structure of the galaxy
distribution and see the BAOs.
Local galaxy surveys:
Sloan Digital Sky Survey (US). 2dF Galaxy Redshift Survey (Aus/UK).
Eisenstein et al (2005) Cole et al. (2005)
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GA
LAXYSURVEY
Dark energy fixes
apparent size of
ruler C
OSMICMIC
ROWAVEBA
CKGROUND
A cosmic ruler
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The WiggleZ Project
Project aim: 240,000 galaxies over 1000 deg2
Measure the BAO scale to 2% at z~0.5-1.
Test for cosmological constant w=-1 at z~0.5-1.
Method: Target UV selected galaxies forming stars so
easy to see. Observe spectra with the Anglo-Australian
Telescope AAOmega spectrograph target up to400 galaxies at once.
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AAOmega
Spectrograph for the 2-degree Fieldrobotic fibre positioner at the AAT.
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AA hardware
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First BAO detection
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The Universe is accelerating we have no ideawhy!
WiggleZ is the only current high-z project
measuring dark energy via cosmic sound. We target star-forming galaxies selected in the
ultra-violet.
So far: marginal detection of the wiggles?
Only the first step future projects needed toget a fuller answer.
Summary