Physical Cosmology 6/6/2016

Transcription

1 Physical Cosmology 6/6/2016 Alessandro Melchiorri slides can be found here: oberon.roma1.infn.it/alessandro/cosmo2016

2 CMB anisotropies The temperature fluctuation in a direction can be expressed as a line-of-sight integral: We have 3 terms: Gravity: photons coming out from CDM potential wells will suffer a redshift. Intrinsic: where we have more baryons we have more photons (tight coupling) and a blue shift. Doppler: baryons move and they leave a doppler effect when scattering off photons.

3 Hu, Sugiyama, Silk, Nature 1997, astro-ph/

4 Integrated Sachs-Wolfe effect Late ISW Early ISW

5 Late and Early ISW Late ISW Late ISW Early ISW Late and Early ISW are on different angular scales. They depend on different parameters. If you vary Neff you vary EISW. If you vary w you vary LISW.

6 Late Integrated Sachs-Wolfe effect while most cmb anisotropies arise on the last scattering surface, some may be induced by passing through a time varying gravitational potential: δt T d Φ( ) = 2 τ τ linear regime integrated Sachs-Wolfe (ISW) non-linear regime Rees-Sciama effect when does the linear potential change? 2 Φ = 4π Ga 2 ρ δ Poisson s equation constant during matter domination decays after curvature or dark energy come to dominate (z~1) induces an additional, uncorrelated layer of large scale anisotropies

7 two independent maps Integrated Sachs-Wolfe map Mostly large angular features Early time map (z > 4) Mostly from last scattering surface Observed map is total of these, and has features of both (3 degree resolution)

8 compare with large scale structure ISW fluctuations are correlated with the galaxy distribution! observer potential depth changes as cmb photons pass through time dependent gravitational potential density of galaxies traces the potential depth since the decay happens slowly, we need to see galaxies at high redshifts (z~1) active galaxies (quasars, radio, or hard x-ray sources) possibility of accidental correlations means full sky needed

9 how do we trace the matter? X-rays from active galaxies HEAO-1 x-ray satellite Galaxy and virtually all visible structures cleaned out Radio galaxies NRAO VLA Sky Survey (NVSS)

10 Fosalba, Gaztanaga 2004

11 5 (old) ISW detections Mean redshift Signal (µk) Bias Catalog Band Reference pm MASS, infrared Afshordi et al pm APM, optical Scranton et al, pm SDSS, optical Fosalba et al pm SDSS high z, optical Padmanabhan et al pm NVSS+HEAO, Radio, X-Rays Boughn & Crittenden 2004

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13 Gravitational Lensing The gravitational effects of intervening matter bend the path of CMB light on its way from the early universe to the Planck telescope. This gravitational lensing distorts our image of the CMB

14 Gravitational Lensing A simulated patch of CMB sky before lensing 10º

15 Gravitational Lensing A simulated patch of CMB sky after lensing 10º

16 Planck dark matter distribution throught CMB lensing This can be obtained using 4-point correlation function

17 Most significative ISW detection is coming by cross correlating Planck with CMB lensing

18 Oscillations are on subdegree angular scales. They need causality to form! First peak gives angular size of horizon at recombination! Large angular scales Anisotropies here just induced by gravity Small angular scales Anisotropies here induced by gravity, photon-baryon pressure and Doppler (not accurate!)

19 CMB polarization - Unlike temperature anisotropies is generated only by scattering (no SW or ISW). - Polarization is sourced mainly by the Doppler term. Peaks in the angular spectrum are out of phase respect to temperature. - Measuring polarization increases the precision on cosmological parameters. - On large angular scale polarization can provide constraints on the reionization optical depth. - CMB polarization provides the best way to detect primordial (created during inflation) gravitational waves.

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23 At redshift 6<z<20 the intergalactic hydrogen is reionized by UV photons emitted by the first structures. A proof of this is the lack of Gunn- Peterson effect in Ly-α systems. We don t know exactly how and when reionization happened. In the most common CMB codes is parametrized as: xe for reion. at zre=10 f=1 Δz=0.1,1.5 The reionization optical depth is given by: Larger zre means larger τ!

24 Parameter degeneracy Some parameter can have very similar effect on the temperature CMB angular spectrum. For example. the spectral index and the optical depth of reionization are essentially anti correlated.

25 Polarization can break the degeneracy! Increasing τ increases the polarization at large angular scales, i.e. on the scales of the horizon at recombination.

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29 Primordial Perturbations Inflation produces the spectrum of primordial perturbations that leads to the formation of structures that we observe today. These perturbations are defined as scalar perturbations. In general relativity, perturbations can be divided in scalar (density), vector (vorticity) and tensor (gravitational waves). Their evolution is independent until perturbations are linear. Inflation also produces vector and tensor perturbations. Vector perturbations fade away and are not detectable. What about tensor perturbations?

30 All inflationary models produce gravity waves at some level. If seen they are extremely supporting evidence for inflation! Temp. Pol. Tensor are present only on super horizon scales at recombination They dissipates inside the horizon. Small polarization is also generated at the horizon crossing.

31 Scalar and tensor are independent and the total spectrum is given by the sum of the two in quadrature. Unfortunately, for temperature the effect of GW is very similar to increasing the optical depth or decrasing ns The GW contribution is parametrized by the ratio computed at 0.05 h/mpc

32 Gravitational Waves and Polarization Polarization is however extremely important! The polarization field can be decomposed in curl-free E mode (that are radial around cold spots and tangential over hot spots) and a divergence-free B mode (vorticity).

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34 Unfortunately also lensing produces B modes. There is a limit to the value of r we can measure from CMB of about r=0.0001

35 Most recent results limits r<0.09 at 95% c.l.

36 Measuring primordial GW can help in discriminating between models of inflation Current best fit model (Starobinsky) predicts r 0.003

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