Galaxies and Cosmology

Galaxies and Cosmology

5 points, vt-2007

Teacher: Göran Östlin

Lectures 10-11

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FRW-models, summary

Properties of the Universe set by3 parameters:m, , k of Which only 2 areIndependent:m + + k = 1

Age of universe for: closed(1), critical(2), open(3), and acellerating(4) models

CMBR spectrum

A perfect black body -> thermal equilibrium when emitted

Evolution of energy densities with scale factor R

Evolution of fundamental interactions with time

inflation?

Evolution of R during inflation

What could have caused inflation?

Equation of state: p = w

Radiation: w=1/3Matter: w0

If w<-1/3 we would get acceleration i.e. Negative pressure makes gravity repulsive!

Could w be a function of time? quintessence

The early universe

Gamov criterium: A reaction may be important as long as its interaction time scale is shorter than the expansion time scale of the universe

Pair production. e.g. + e- + e+

reaction balance set by temperature, e.g: e + n e- + p

As long as mAc2 < kT a particle ’A’ may be kept in equilibrium, then ”freeze out”

The early universe…

Baryogenesis: matter-antimatter equality broken, Possibly by the decay of a so called X-bosonNet amount of matterPhoton to baryon ratio = 109

Neutrino freeze out (decoupling) at t=0.7s Electron-positron pair production ceased and theAnnihilation of existing pairs heated up radiation and Matter but not the neutrinos that had already decoupled

Primordial nucleosynthesis

All fusion of hydrogen to heavier elements go throughthe stage of deuterium. p + n D +

However, D can be dissociated by photons more energetic than 2.2 Mev

Since there are many more photons than baryonsThis will occur frequently enough also at much lowerTemperatures than kT=2.2 Mev ~1010 K

Nucleosynthesis inhibited until the D productionrate was higher than the distruction rate (109K, t=200s)

DEUTERIUM BOTTLENECK

Primordial nucleosynthesis…However, neutron to proton ratio was fixed earlier (t=1s) when the neutrinos froze out: N(n)/N(p)=0.22

Since then until t=200s, some neutrons have decayedso N(n)/N(p)=0.16

Basically all leftover n ends up in D and almost all of that becomes He. Nothing heavier than Li is made.

The He adundance is therefore determined by (since we know the current CMBR photon density this gives us bar)

Other trace elements: D, 3He, 7Li depend more strongly…

Primordial nucleo-

synthesis…

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Only a smallFraction of allMatter may beBaryonic

Still larger than The luminous Matter density

Galaxies could be baryonic?

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(re)combinationSimilarly to above, the vast amount of photons canKeep hydrogen ionised to temperatures well below13.6 eV. But when T<4500 K the number of energetic Enough photons is to small and protons and electronscan combine to form neutral hydrogen

Matter and radiation decouples

Last scattering surface at z = 1100 (T=3000K)

Leads to dramatic drop in pressure for the matter

Observable as 3000/1100=3K CMBR, no lines since>>1 and z >>1

CMBR according to COBE

Penzias & Wilson

Cosmic microwaveBackground

Early universeHot & Dense

Dipole

Last scattering ”surface”

Structure/galaxy formation

The concept of Jeans mass

Gravity vs pressure,

Static medium: M > Mjeans exponential growthExpanding EdS: M > Mjeans linear growthExpanding Open universe: M > Mjeans no growth

Fluctuation spectrum:

EdS: temperature fluctuations in CMBR expectedat the 10-3 level, but only 10-5 observed

Dark matter comes to rescue!

€

=δ /ρ

ρ(x ) = δρ(x ) + ρ

€

∝ r−(n +3)/ 2, Δ∝ M−(n +3)/ 6

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Evolution of Jeans mass with scale factor with scale factor R

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Hierarchical growth of structure

CMBR fluctuations

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First acoustic peak = standard rod!Height set by ΩBaryon

At larger scales: Sachs-Wolfe

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Problems with standard BBI. Magnetic Monopoles

Problems with standard BBII. Horizon problem

Problems with standard BBIII. Flatness Problem

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Problems with standard BBIV. Origin of structure

Inflation enlargesthe scale of quantumfluctuations

Microscopic

Becomes

Macroscopic

The nature of dark matter

Baryonic dark matterHot vs cold non-baryonic dark matter: e.g. Nutrinos vs WIMPs

Nature of dark energy

-Cosmological constant-Vaccuum energy-Quintessence-String/Brane theory, extra dimensions

Observations of the distant universe

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HSTUltra Deep Field

2 weeks of exposure

Most distant galaxies at z=6

Problem: most of the light comes out in the infrared

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Lookback time and age

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Luminosity distance and angular size distance

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Redshifting galaxies

LBGsLyaGsEROs

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”Madau-plot”

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Madau plot isvery sensitiveto asssumptionsabout dust

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Hierarchical growth of structure

Galaxy formation is a continous process

Each big galaxy has had one major merger since z=1

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Closing in on the dark ages…

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JWST

Some future observational tools

ALMA, sub-mm, 64 antennae

JWST “the first light machine”6.5 m

OWL the overwhelmingly large telescope +50m