galaxies and cosmology 5 points, vt-2007 teacher: göran Östlin lecture 12
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Galaxies and Cosmology
5 points, vt-2007
Teacher: Göran Östlin
Lecture 12
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Lecture 12 contents
• Cosmological problems
• Observational Cosmology: - Galaxy formation and evolution: from
popIII to today - Cosmological parameters:
H0, q0, Ω (bar, matter, DM), T0
• Summary of course
Problems with standard BBIII. Flatness Problem
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k is independent of R and time, but Ω rapidly approaches the value 1.0 for small R
Alternatively: if k0 one would expect Ω0 << 1 or Ω0 >> 1To be compatible with todays Ω0 which is of order one, then Ω(tPlanck) must have been = 1.000…(55 zeros)..001-Enormous fine tuning!
€
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Ω−1 =k c 2
R2H 2
Problems with standard BBIV. Origin of structure
Inflation enlargesthe scale of quantumfluctuations
Microscopic
Becomes
Macroscopic
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
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
The anthropic principle-is the universe there for us or do we exist because the universe looks like it does-Science of philosophy?
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 =δ /ρ
ρ(x ) = δρ(x ) + ρ
€
Δ ∝ 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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observations
Numerical simulation
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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
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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Closing in on the dark ages…
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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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Different phases of the merger of two galaxies with central supermassive black holes. From top to bottom, the individual images of the sequence show the gas of two colliding spiral galaxies. After the first encounter, they first separate again from each other, but then come together for a second encounter and subsequent coalescence. Gravity is driving gas into the centers of the galaxies and leads to the formation of extended tidal arms. As a result of the nuclear inflow, the black holes grow strongly in mass during a quasar phase. This phase lasts up to 100 million years and releases enough energy to heat the gas and to expel it into extragalactic space. At the end an elliptical galaxy remains (its stars are not shown in the image sequence) which contains almost no residual gas and hosts at its center the merged pair of supermassive black holes.
AGN feedback
Some future observational tools
ALMA, sub-mm, 64 antennae
JWST “the first light machine”6.5 m
OWL the overwhelmingly large telescope +50m
Properties of the Universe set by3 parameters: Ωm, Ω, Ωk of Which only 2 areIndependent: Ωm + Ω + Ωk = 1
CMBR fluctuations
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First acoustic peak = standard rod!Height set by ΩBaryon
At larger scales: Sachs-Wolfe