Galaxies and Cosmology 5 points, vt-2007 Teacher: Göran Östlin Lectures 10-11.
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Transcript of Galaxies and Cosmology 5 points, vt-2007 Teacher: Göran Östlin Lectures 10-11.
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