Galaxies and Cosmology 5 points, vt-2007 Teacher: Göran Östlin Lecture 6.
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Transcript of Galaxies and Cosmology 5 points, vt-2007 Teacher: Göran Östlin Lecture 6.
Galaxies and Cosmology
5 points, vt-2007
Teacher: Göran Östlin
Lecture 6
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Distances to galaxies (JL 2.4)
- Standard candles (& rods)
F = L / 4 d2 inverse square law
= D / d angular diameter vs distance
Cepheids P-L relation
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Cepheid PL relation
Type II SNe
L = 4 R2 T4 for black bodies
F1 / F0 = L1 / L0 = R12
T14 / R0
2 T0
4
F1 / F0 observed photometricallyT from Black Body approxR1 / R0from expansion velocity Fainter than Type Ia, less well calibrated
Surface brightness fluctuations
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Galaxies and scaling laws
Galaxies have broad luminosity function
Spirals: Tully-Fisher: L V4max inclination
Ellipticals: Faber-Jacksson: L v4
=> learn us about galaxies too
(3rd) Brightest cluster galaxy
Spiral galaxy diameters
Other standard candles…
- Tip of RGB- Main sequence fitting- eclipsing binaries- Brightest red or blue supergiant- globular cluster luminosity function- planetary nebulae luminosity function
-Etc…
Redshisfts…
z = (obs - em)/ em = obs / em - 1 = /
vr = z c
z = H0 d / c => v r= H0 d
Valid up to z 0.2
NB Special relativistic formula not more accurateGeneral relativistic description of space-time required
Gravitational lens time delay
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Einstein cross
Complications
-Deviations from a pure Hubble flow, peculiar motions
-Dust extinction
-Malmqvist bias
-Evolutionary effects
Acoustic horizon in CMBR
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Theoretical cosmology
Problems with Newtonian Gravity and Mechanics:GravityInertial frames - absolute space and time
General Relativity - matter curves space (& time), EPG + g = -8G T / c4
G, g, T are tensors
Geometry: line element
Cosmological principle: isotropy, homogeneity
Gravity can in General Relativity be regarded as a space curvature rather than a force
Orbit of earth a straight line in space-time
Geometrical cosmology: Line elements
€
ds2 = dx 2 + dy 2
ds2 = dx 2 + dy 2 + dz2
ds2 = dr2 + r2(dθ 2 + sin2θ dφ2)
ds2 = r2(dθ 2 + sin2θ dφ2)
ds2 = dx 2 + dy 2 + dz2 − c 2dt 2
ds2 < 0
ds2 = 0
ds2 > 0
2-dim cartesian
3-dim cartesian
3-dim spherical
2-dim curved space
Special relativity
Timelike separation
Null separation (light)
Spacelike separation
Robertson-Walker line element
€
ds2 = c 2dt 2 − R2(t)dr2
1− kr2+ r2(dθ 2 + sin2θ dφ2)
⎡
⎣ ⎢
⎤
⎦ ⎥
Simplest 4-dim (3 space, 1 time) space that fulfills the cosmological principle
Only R(t) changes with time -> homogeneously expanding or contracting space