astrophysics i, lecture slides – chapter 9, eth zurichastrophysics i, lecture slides – chapter...
Post on 14-Jul-2020
1 Views
Preview:
TRANSCRIPT
Hubble diagram for Cepheid distances
from Choudhuri
Astrophysics I, Lecture Slides – Chapter 9, ETH Zurich
1
Redshift surveys
from Choudhuri 2
from Choudhuri 3
A spherical and a hyperbolic surface
from Choudhuri 4
from Choudhuri 5
Newtonian cosmology model
from Choudhuri6
Solutions of the Friedmann equation
from Choudhuri 7
Cosmic Microwave Background (CMB)
from Choudhuri 8
An accelerating universe ?
SN Ia at large z are too faint for aFriedmann-type universe
Interpretation: accelerating expansion Λ universe is flat universe is older
but: Λ unclear
9
from frigg.physastro.mnsu.edu 10
from Choudhuri 11
Primordial abundances vs. η=nb/nγ
from Choudhuri 12
CMB-fluctuationstemperature fluctuation at a level of ΔT/T ≈ 10-5
these are the seeds for the later structure formation
from Choudhuri 13
Structure formation
from Choudhuri 14
Lookback-time vs redshift- with the best telescopes (HST, VLT) the structure formation in the ``early’’
Universe can be observed directly - bright objects can be observed at distances of
> 5 billion ly = lookback time > 5 billion years telescopes are time machines
relation between • redshift and • look-back time
(relative to age of Universe)
15
HDFHubble Deep Field
HDF was 1995 the first very deep observation of galaxies in ther “early” Universe
field: 2.5’ x 2.5’(3x10-8 of the sky)
~3000 objects(~20 stars)
The most distant objects in this field emitted there light only 2-5 billion years after the big bang.
next slide: section on the lower right
16
z=2.80
z=0.50
z=0.68
z=1.24
z=0.76
z=1.06
z=1.01 17
Galaxy statisticsnumber of galaxies per solid angle brighter than a given magnitude limit
in HDF, there are about 10x more galaxies(data points) than expected, assuming that galaxies and galaxy numbers do not change with time (solid lines)
- the excess is particularly strong for irregular/peculiar/merger galaxies(lower right)
Interpretations- galaxies were in the past on average
10x brighter (higher star formation rate) therefore we see more bright galaxies
than expected big excess for colliding galaxies which
result from the ``first’’ assembly of gasrich matter components
GaGalaxy statistic in the HDF(for all galaxies (a) und special types (b,c,d); aus Abraham et al. 1996, (MNRAS 279, L47)
18
Quasar number density vs redshift
from Choudhuri
many bright quasars appear at z ≈ 2.5
- BH > 109 Msun
almost no bright quasar at z < 0.2 (last 1 billion years)
Feeding of black holes stopped
19
Lyα forest – evolution of the intergalactic medium
- quasars are good background sources for HI Lyα absorption (low ionization clouds)- Lyα along line of sight has lower redshift (to the blue of the Lyα emission)- yields good statistics on the distribution of clouds
20
Reionization of the Universe
3C 273 z = 0.16
SDSS z = 5.80
21
top related