russell johnston dept of physics and astronomy university of glasgow
TRANSCRIPT
Russell Johnston
Dept of Physics and AstronomyUniversity of Glasgow
Edwin Hubble
Hubble measured the shift in colour, or wavelength, of the light from distant galaxies.
Galaxy
Hubble measured the shift in colour, or wavelength, of the light from distant galaxies.
Galaxy
Laboratory
Wavelength
Energy
Spectrum of a nearby galaxy
Spectrum of a Distant Galaxy
Hubble’s Law: 1929Hubble’s Law: 1929
Distant galaxies are receding from us with a speed proportional to their distance
Spacetime is expanding like the surface of a balloon.
As the balloon expands, galaxies are carried farther apart
Although Hubble got the expansion law correct, his measurement of the current rate of expansion was quite wrong, and took many decades to correct.
Measuring the Hubble constant was a key project of the Hubble Space Telescope
More recently we have extended the Hubble diagram to great distances, using e.g. Supernovae….
Region probed by
Hubble’s data
redshift
‘Speeding up’ model
‘Slowing down’ model
Models with different shapes
Hubble’s law for nearby supernovae
mea
sure
of
dist
ance
….This has led to a remarkable discovery:The expansion of the Universe is speeding up!
What is driving the cosmic acceleration?…What is driving the cosmic acceleration?…
Around Galaxies
0
50
100
150
200
250
300
0 20 40 60 80
Distance from the Galaxy Centre (kpc)
Orb
ital v
eloc
ity (
km/s
)
Typical size of galaxy disk
What we seeWhat we see
What is really there.
We can also measure the redshifts of many galaxies.
We call this a redshift survey.
Redshift surveys can tell us many useful things:
• How galaxies cluster in space
• How galaxies evolve in time
• Different types of galaxy and where (and when) they are found
• How galaxies formed in the first place
• How much dark matter and dark energy…
And
The First Redshift Surveys• CfA Survey #1 : 1977 - 1982
CfA # 1
• Surveyed a total of 1100 galaxies
• Marc Davis,
John Tonry
Dave Latham,
John Huchra,
• Redshift range: out to z
0.05
Our own Galaxy
de Lapparent, Geller, and Huchra (1986), ApJ, 302, L1
de Lapparent, Geller, and Huchra (1986), ApJ, 302, L1
Filament
Rich cluster
Void?
CfA # 2
The First Redshift Surveys• CfA Survey #2 : 1985 -1995• John Huchra &• Surveyed a total of 18,000 galaxies
Margaret Geller
• Redshift range: out to z
0.05 208 Mpc
Redshift surveys (mid-
1980s)
1 Mpc = 3.26 milion light years
1 Mpc = 3.26 milion light years
The largest structures in LCRS are much smaller thanthe survey size
The size of thestructures issimilar in both samples
LCRS
1995 (LAS CAMPANAS)
The First Redshift Surveys• IRAS PSCz : 1992 – 1996, 15,000 galaxies• Team originally consisted of around 24 members including:
• Catalogued over 83% of the sky -
Will Sutherland,
Steve Maddox,
Largest full sky survey.
Will Saunders,Carlos Frenk &
Seb Oliver,
Luis Teodoro.
Surveys….
The Next Generation
• Ran from 1998 to 2003.• Used the multifibre spectrograph on the Anglo Australian Telescope. • The survey covered two strips : NGP -
75 10
80 15 SGP -
• Photometry was taken from the APM galaxy catalogue. • Galaxies brighter than
19.45b
m
• Recovered a total of 245,591 redshifts, 220,000 of which were galaxies out to 0.2z
The Two Degree Field Galaxy Redshift Survey
(2dFGRS)
The Two Degree Field Galaxy Redshift Survey
(2dFGRS)
• 35 collaborators fro UK, Australia and the US.• including: Carlos Frenk, Matthew Colles, Richard Ellis, Ofer Lahav, John Peacock, Will Sutherland…. and these guys:
Keith Taylor
Simon Driver
Karl Glazebrook Nick
Cross
Shaun Cole
Peder Norberg
Warrick Couch
The Two Degree Field Galaxy Redshift Survey
(2dFGRS)
The Two Degree Field Galaxy Redshift Survey
(2dFGRS)
= 100 Mpc diameter
The Sloan Digital Sky Survey
(SDSS)• Most ambitious ongoing
survey to date.• Began in early nineties and was due to complete in 2008 …. ish
• Uses a dedicated 2.5m telescope on Apache Point, new Mexico and a pair of spectrographs that measure more than 600 galaxy spectra in a single observation.
• Currently on data release 5 which contains 674749 galaxies.
• On completion will have surveyed over 1 million galaxies.• The Survey has over 150 collaborators at 26 institutions
The Sloan Digital Sky Survey
(SDSS)
SDSS
CfA
Sloan Digital Sky Survey: The Footprint of the Survey
Area and Size of Redshift Surveys
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E+08
1.00E+09
1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08 1.00E+09 1.00E+10 1.00E+11
Volume in Mpc 3
No
of
ob
jec
ts
LCRS
SDSSmain
SDSSred
SDSSabs line
SDSSphoto-z
2dFRCfA+SSRS
SAPMQDOT
2dF
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E+08
1.00E+09
1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08 1.00E+09 1.00E+10 1.00E+11
Volume in Mpc 3
No
of
ob
jec
ts
LCRS
SDSSmain
SDSSred
SDSSabs line
SDSSphoto-z
2dFRCfA+SSRS
SAPMQDOT
2dF
CMBR fluctuations, 380000 years after the Big Bang, are the seeds of today’s galaxies
The pattern of CMBR temperature fluctuations can be used to constrain the background cosmological model and its parameters
Galaxies and Cosmology: the Basic Paradigm
CMBR fluctuations, 400000 years after the Big Bang, are the seeds of today’s galaxies
The pattern of CMBR temperature fluctuations can be used to constrain the background cosmological model and its parameters
Both the CMBR and present-day galaxy clustering favour :
Galaxies and Cosmology: the Basic Paradigm
CDM
Cold dark matter + non-zero cosmological constant
CMBR fluctuations, 400000 years after the Big Bang, are the seeds of today’s galaxies
The pattern of CMBR temperature fluctuations can be used to constrain the background cosmological model and its parameters
Both the CMBR and present-day galaxy clustering favour :
Galaxies and Cosmology: the Basic Paradigm
CDM
Cold dark matter + non-zero cosmological constant
The Concordance ModelThe Concordance Model
CDM
From Lineweaver (1998)
The cosmological constant now dominates over CDM and
baryonic dark matter (i.e. atoms).
It is not yet clear if is constant, or perhaps evolves with
time.
More generally, is referred to as
‘Dark Energy’.
Dark Energy
Cold Dark Matter
Ato
ms
The cosmological constant now dominates over CDM and
baryonic dark matter (i.e. atoms).
It is not yet clear if is constant, or perhaps evolves with
time.
More generally, is referred to as
‘Dark Energy’.
Dark Energy
Cold Dark Matter
Ato
ms
The cosmological constant now dominates over CDM and
baryonic dark matter (i.e. atoms).
It is not yet clear if is constant, or perhaps evolves with
time.
More generally, is referred to as
‘Dark Energy’.
Unlike ‘normal’ matter, dark
energy is gravitationally repulsive :
it is causing the expansion of the
Universe to accelerate.
Dark Energy
Cold Dark Matter
Ato
ms
The cosmological constant now dominates over CDM and
baryonic dark matter (i.e. atoms).
It is not yet clear if is constant, or perhaps evolves with
time.
More generally, is referred to as
‘Dark Energy’.
Unlike ‘normal’ matter, dark
energy is gravitationally repulsive :
it is causing the expansion of the
Universe to accelerate.
This affects the rate of growth of
cosmic structure, which we can model
via computer simulations
Hierarchical clustering:
Galaxies form out of the mergers of fragments: CDM halos at high redshift.
Clusters form where filaments and sheets of matter intersect
140 Mpc
11 Gyr ago
Hierarchical clustering:
Galaxies form out of the mergers of fragments: CDM halos at high redshift.
Clusters form where filaments and sheets of matter intersect
140 Mpc
8 Gyr ago
Hierarchical clustering:
Galaxies form out of the mergers of fragments: CDM halos at high redshift.
Clusters form where filaments and sheets of matter intersect
140 Mpc
Present day
Hierarchical clustering:
Galaxies form out of the mergers of fragments: CDM halos at high redshift.
Clusters form where filaments and sheets of matter intersect
20 Mpc
11 Gyr ago
Hierarchical clustering:
Galaxies form out of the mergers of fragments: CDM halos at high redshift.
Clusters form where filaments and sheets of matter intersect
8 Gyr ago
20 Mpc
Hierarchical clustering:
Galaxies form out of the mergers of fragments: CDM halos at high redshift.
Clusters form where filaments and sheets of matter intersect
Present day
20 Mpc
Hierarchical clustering:
Galaxies form out of the mergers of fragments: CDM halos at high redshift.
Clusters form where filaments and sheets of matter intersect
11 Gyr ago
20 Mpc
Hierarchical clustering:
Galaxies form out of the mergers of fragments: CDM halos at high redshift.
Clusters form where filaments and sheets of matter intersect
8 Gyr ago
20 Mpc
Hierarchical clustering:
Galaxies form out of the mergers of fragments: CDM halos at high redshift.
Clusters form where filaments and sheets of matter intersect
Present day
20 Mpc
Which simulation model matches the observations?...
Hubble’s tuning fork classification
We see spiral and elliptical galaxies…
Morphological Segregation
Nowadays we find few spiral galaxies in rich clusters. This is thought to be because the spiral disks are disrupted by tidal forces…
Morphological Segregation
Nowadays we find few spiral galaxies in rich clusters. This is thought to be because the spiral disks are disrupted by tidal forces…
…Conversely, many ellipticals (and some spirals) may have formed from galaxy mergers.
See talk by Bonnie Steves
A long time ago,
in a galaxy far, far away…
z = 2.0
Light travel time =10.3 billion years
z = 2.1
Light travel time =10.5 billion years
z = 2.2
Light travel time =10.6 billion years
z = 2.3
Light travel time =10.8 billion years
z = 2.4
Light travel time =10.9 billion years
z = 2.5
Light travel time =11.0 billion years
z = 2.6
Light travel time =11.1 billion years
z = 2.7
Light travel time =11.2 billion years
z = 2.8
Light travel time =11.3 billion years
z = 2.9
Light travel time =11.4 billion years
z = 3.0
Light travel time =11.5 billion years
z = 3.1
Light travel time =11.6 billion years
z = 3.2
Light travel time =11.6 billion years
z = 3.3
Light travel time =11.7 billion years
z = 3.4
Light travel time =11.8 billion years
z = 3.6
Light travel time =11.9 billion years
z = 3.7
Light travel time =11.9 billion years
z = 3.8
Light travel time =12.0 billion years
z = 4.0
Light travel time =12.1 billion years
z = 4.1
Light travel time =12.1 billion years
z = 4.3
Light travel time =12.2 billion years
z = 4.4
Light travel time =12.2 billion years
z = 4.5
Light travel time =12.3 billion years
z = 4.6
Light travel time =12.3 billion years
z = 5.0
Light travel time =12.5 billion years