1. Astronomy 305/Frontiers in Astronomy
Class web site:
Office: Darwin 329A
(707)
Best way to reach me:
11/11/03
Prof. Lynn Cominsky

2. Group 11
Great job, group 11!
11/11/03
Prof. Lynn Cominsky

3. What does the Universe look like?
What happens when galaxies collide?
How do galaxies cluster?
What are the largest structures in the Universe?
What other types of background radiation exist?
Summary of scales in the Universe
11/11/03
Prof. Lynn Cominsky

4. Cartwheel Galaxy Wheel shape was formed from collision of two galaxies
Bright stars are forming at the edges of the wheel (105 light years in diameter)
Intruder galaxy is no longer visible
This is from HST
11/11/03
Prof. Lynn Cominsky

5. Collisions and Mergers movie
Galaxy collisions contribute to large scale structure formation
Note: galaxies do not make noise when they collide!
11/11/03
Prof. Lynn Cominsky

6. More Galaxy Collision movies
11/11/03
Prof. Lynn Cominsky

7. Galaxy Harassment Spirals merge to form ellipticals
Biggest elliptical cannibalizes the others to form one giant elliptical in the center of the cluster
Dwarf ellipticals are formed by harassment (high velocity encounters) of low-mass spirals
Detectable arcs of debris are left over – providing fuel for quasars
11/11/03
Prof. Lynn Cominsky

8. Galaxy Harassment movie
Gas is red
Stars are yellow and in a disk initially
Dark matter is blue and in a halo initially
Green are other galaxies in the cluster
Initial spiral becomes warped, and eventually elliptical
11/11/03
Prof. Lynn Cominsky

9. Virgo cluster of galaxies
The Virgo cluster of galaxies is about 65 million light years away
It contains about 2500 galaxies
It is dominated by M87
M87
11/11/03
Prof. Lynn Cominsky

10. Virgo Cluster It is the nearest rich cluster of galaxies
Classification - irregular
Covers about 100o of sky or at its distance it spreads out over tens of millions of light years
Recessional velocity is about 0.3% of velocity of light
X-ray emission concentrated around individual galaxies, particularly M84 and M86
The strong radio galaxy M87 in the Virgo cluster is also a strong source of X-rays
11/11/03
Prof. Lynn Cominsky

11. X-ray emission from Clusters
Gas in clusters of galaxies is held by mass where:
Mass of hot gas is more than 3 times the mass of the visible light galaxies in the Virgo cluster
Strongest X-rays are around M87
Virgo/ROSAT
M = V2R G
11/11/03
Prof. Lynn Cominsky

12. Distances to Galaxy Clusters
Brightest Cluster Galaxies: The brightest galaxy in a cluster of galaxies has been used as a standard candle.
But: rich clusters with many galaxies will probably have the most luminous galaxies even though these galaxies are very rare, while the brightest galaxy in less rich clusters are probably not as bright
11/11/03
Prof. Lynn Cominsky

13. Standard Candles
Objects with known luminosities that can be used to calculate distance
Fobs = Ltrue/(4pd2) where
Fobs = flux observed at Earth
Ltrue = true brightness at source
d = distance from Earth to source
movie
11/11/03
Prof. Lynn Cominsky

14. Types of Galaxy Clusters
Regular clusters
concentrated central core
well-defined spherical structure
often dominated by a giant galaxy
usually quite rich, M~1015 Mo
most galaxies are elliptical or lenticular
Irregular clusters
no well-defined center
~half the galaxies are spirals
Often contain subclusters
Probably not steady state
11/11/03
Prof. Lynn Cominsky

15. Hydra Cluster Distance of 840 million light years
Several hundred galaxies in the cluster
35 million degree gas in center rising to 40 million in the outside
Several million light years across the gas cloud
Optical/La Palma
11/11/03
Prof. Lynn Cominsky

16. Hydra Cluster
X-ray/Chandra
Radio/NRAO
11/11/03
Prof. Lynn Cominsky

17. Cluster Formation
Formation and evolution of a galaxy cluster (from T6 group at Los Alamos)
Evolution of a Cd galaxy cluster (from John Dubinski at CITA)
movies
11/11/03
Prof. Lynn Cominsky

18. How clusters affect galaxy evolution
movie
Ram pressure and turbulent stripping of gas from a spiral galaxy as it falls through the hot ICM of a rich galaxy cluster (by Vicent Quilis with Ben Moore)
The galaxy model is 3d with a stellar disk, bulge + dark matter halo. The colours show the gas density in a thin slice centered on the disk
11/11/03
Prof. Lynn Cominsky

19. Small Cluster
X-rays from this smaller cluster were discovered by ROSAT
Hot gas engulfs the two bright elliptical galaxies
It is about 500 million light years away
11/11/03
Prof. Lynn Cominsky

20. Very Distant Cluster It is the most distant cluster discovered by HST
This is a very red cluster, located at Z~1
It is the most distant cluster discovered by HST
It may be too far away to have formed in a dense universe
11/11/03
Prof. Lynn Cominsky

21. Very Distant Cluster It is also very red
This cluster is 8 billion light years away, so it formed when the universe was half its present age
It is also very red
It should not exist if the Universe is dense
11/11/03
Prof. Lynn Cominsky

22. Merging Clusters A2256 cluster has about 500 galaxies
It is about 10 million light years across
It is about 1 billion light years away
The 80 million degree gas is brightest in the center where two clusters are merging
11/11/03
Prof. Lynn Cominsky

23. Merging Clusters A2142 cluster
The 50 million degree gas is coolest in the center where two clusters have finished merging
The gas outside the center is 100 million degrees – heated by the collision
Chandra image
11/11/03
Prof. Lynn Cominsky

24. Cannibal Cluster
ESO/Optical
A3827 is about 1.5 billion light years away
The central dominant galaxy is eating five smaller galaxies
11/11/03
Prof. Lynn Cominsky

25. Coma Cluster Coma cluster has about 1000 galaxies
It is located near the north galactic pole
It is about 250 million light years away (80 Mpc)
Large bright central cluster is merging with smaller galaxy group at the lower right
3 Mpc
11/11/03
Prof. Lynn Cominsky

26. Perseus Cluster
One of the closest galaxy clusters at a distance of 300 million light years
Part of the Perseus Pisces supercluster which is 15 degrees across and has over 1000 galaxies
11/11/03
Prof. Lynn Cominsky

27. Local Supercluster
The Local supercluster contains the Virgo cluster of galaxies as well as about 50 galaxy groups
11/11/03
Prof. Lynn Cominsky

28. Superclusters Local Supercluster
Superclusters usually have 3-10 clusters of galaxies
They are not gravitationally bound
Our local supercluster contains the Virgo cluster (at 16 Mpc) and extends about Mpc
11/11/03
Prof. Lynn Cominsky

29. “Stickman”
“Slice” –style Redshift survey pioneered by Margaret Geller, Marc Davis and John Huchra
The body of the stickman is due to the Coma cluster
His arms form “walls”
Distance is plotted vertically as given by redshifts
11/11/03
Prof. Lynn Cominsky

30. Las Campanas Survey Largest redshift survey
Done by Shectman et al.
Largest redshift survey
Clearly shows walls and voids
75-80% of space is devoid of bright galaxies
Typical distance between 2 galaxies is around 7.5 Mpc
Typical distance between 2 clusters is around 20 Mpc
11/11/03
Prof. Lynn Cominsky

31. Flyby universe movie
Las Campanas data – notice the walls and voids as you fly by
11/11/03
Prof. Lynn Cominsky

32. Walls and Voids Universe looks like soap bubbles in 3D
Galaxies occur on the bubble surfaces
Superclusters are formed where bubbles merge
Walls are made of elongated superclusters – the largest is the “Great Wall” - about 100 Mpc in length at a distance of 100 Mpc
Voids are about 100 Mpc in diameter – are 90% of space
Clusters of galaxies are bright spots on the walls
11/11/03
Prof. Lynn Cominsky

33. Large Scale Structure formation
Comparison of the 2df galaxy redshift survey to mock catalogue constructed from a Lambda CDM simulation (from Ben Moore)
movie
11/11/03
Prof. Lynn Cominsky

34. XMM-Newton LSS Survey X-ray emitting clusters of galaxies
About 15 per square degree
11/11/03
Prof. Lynn Cominsky

35. Lyman-alpha forest studies
Lyman alpha is the name of the electron transition from n=1 to n=2 in Hydrogen
When the H atom is hit by a photon, the electron can get enough energy to make this transition, and the photon is removed from the initial beam from the source
11/11/03
Prof. Lynn Cominsky

36. Lyman-alpha forest studies
The observer sees light from the distant quasar that is absorbed due to intervening H-clouds
However, because the Universe is expanding, the Ly-a absorption lines occur at different wavelengths, which tell you the distance to each cloud
quasar
clouds
11/11/03
Prof. Lynn Cominsky

37. Quasar clustering studies
Measurements of positions of QSOs can be used to trace large scale structure
This shows the spectra of 10 QSOs as a function of redshift
11/11/03
Prof. Lynn Cominsky

38. Quasar clustering studies
2dF survey measured redshifts from 250,000 galaxies and 23,000 QSOs
Used camera with two-degree wide field on AAT to measure up to 400 redshifts simultaneously
11/11/03
Prof. Lynn Cominsky

39. 2dF results Walls and voids also seen in southern hemisphere 11/11/03
Prof. Lynn Cominsky

40. Formation of Large Scale Structure
Simulation by Martin White shows the evolution of structure starting with fluctuations in the Cosmic Microwave Background
movie
11/11/03
Prof. Lynn Cominsky

41. The End of Greatness
movie
Most recent surveys are so large that the largest structures (about 100 Mpc) are smaller than the survey size
This is a 200 Mpc simulation from Ben Moore (using LCDM)
11/11/03
Prof. Lynn Cominsky

42. Where are we going?
The Milky Way Galaxy is falling towards the Virgo cluster at ~300 km/s
The Virgo cluster is falling towards the Hydra-Centaurus supercluster also at ~300 km/s
But the Hydra-Centaurus cluster is also falling towards something…..
11/11/03
Prof. Lynn Cominsky

43. Abell 3627 near the Great Attractor
~1016 solar masses concentrated 65 Mpc away in the direction of Centaurus
Abell 3627 near the Great Attractor
The “Great Attractor” seems to be pulling in the Hydra-Centaurus super-cluster
But only 10% that amount of visible matter can be seen!
11/11/03
Prof. Lynn Cominsky

44. Wedge Plot Activity These data are from CLEA’s LSS lab
Each group should plot 20 of the galaxies on the wedge plot transparency
Then we will put all the plots together
How many clusters do you see?
Why is the wedge plot a better representation of the measurements than the linear plot?
11/11/03
Prof. Lynn Cominsky

45. Scales in the Universe Solar system
12 billion km in diameter
Milky Way Galaxy  40,000 pc (~120,000 light years)
Local Group  few Mpc
Larger Cluster  several Mpc
Great Wall  100 Mpc
Observable Universe  3,000-6,000 Mpc (10-20 billion light years)
11/11/03
Prof. Lynn Cominsky

46. Infrared Background
The Cosmic InfraRed Background (CIRB) is the radiation from stars in many faint galaxies.
It is what is left over after emission from our Solar System and our Galaxy has been subtracted away
Near IR is redshifted starlight from distant galaxies
Far IR is starlight absorbed by dust and reemitted
11/11/03
Prof. Lynn Cominsky

47. Infrared Background Reemitted by dust Red shifted starlight CMB
11/11/03
Prof. Lynn Cominsky

48. Zodiacal Light
Diffuse visible light reflected from interplanetary dust
Orbits in same plane as planets
Brightest (in North) in fall and spring
11/11/03
Prof. Lynn Cominsky

49. Ultraviolet Background
The last spectral region to be explored in detail
Narrow bands have been searched
Many mechanisms exist across the UV band
Fluorescent emission from molecular H2
Emission lines from highly ionized atoms
Hot intergalactic medium?
Shock heating from cosmic structure formation?
11/11/03
Prof. Lynn Cominsky

50. X-ray Background ROSAT 0.75 keV map
Shows smooth blue background plus bright superbubble ring at D=150 pc with R= ~100 pc
11/11/03
Prof. Lynn Cominsky

51. X-ray Background Chandra to the rescue!
Discovered over 35 years ago in rocket flights
Early theories explained the X-ray background as a diffuse, hot gas which filled the Universe
Data from Einstein Observatory showed about 50% of the background could be due to quasars
ROSAT data explained about 60% of the 1-2 keV X-ray background with quasars
However flux and energy spectra did not add up correctly if the background was all quasars
Chandra to the rescue!
11/11/03
Prof. Lynn Cominsky

52. Chandra data
At least 80% of X-ray background is made of discrete sources including two new types:
Very distant galaxies with faint black holes
Bright black holes without visible galaxies
Results were from comparing Chandra data to deep optical surveys from Keck
11/11/03
Prof. Lynn Cominsky

53. CGRO/EGRET data
30-40% of gamma-ray background is unresolved and extragalactic in origin
11/11/03
Prof. Lynn Cominsky

54. Gamma-ray Background
Simulated sky as seen by GLAST after 1 year of observation
Key goal to determine if extra-galactic gamma-radiation is from discrete sources
11/11/03
Prof. Lynn Cominsky

55. Backgrounds in the Universe
Cosmic Microwave Background – cooling relic of the Big Bang
Infrared – faint stars in distant galaxies and nearby dusty stars
Visible – local zodiacal light
Ultraviolet – still to be measured
X-ray – unresolved distant black holes in galaxy cores
Gamma-ray – probably similar to X-ray
11/11/03
Prof. Lynn Cominsky

56. Modeling the Universe
Spend about 30 minutes building a model of the Universe with a partner
You may also do just a part of the Universe, such as the solar system or a galaxy
What features of the Universe does your model represent? Misrepresent?
What things have you left out entirely?
What questions came up as you built this model in your group?
11/11/03
Prof. Lynn Cominsky

57. Web Resources
Astronomy picture of the Day
Imagine the Universe
On-line Journey through Astronomy
Space Telescope Science Institute
GLAST project outreach web site
Chandra X-ray Background Results
11/11/03
Prof. Lynn Cominsky

58. Web Resources
On-line Journey through Astronomy
J. C. Evans Astronomy 103 Course eNotes/Html/Lec08/Lec08_pt1_universeClusters.htm
Martin White’s Large Scale Structure
XMM-Newton Large Scale Structure Survey
J. Cohn’s Lyman alpha Forest pages
11/11/03
Prof. Lynn Cominsky

59. Web Resources
T-6 Group at LANL animations and picture
John Dubinski’s Big cluster simulations
2DF redshift survey project
Ben Moore’s N-body simulations
11/11/03
Prof. Lynn Cominsky

60. Web Resources
Ned Wright’s ABCs of Distance and CMIRB
Ray White’s Cluster of Galaxies Mug Shots
Cambridge Cosmology Pages
Jimmy Imamura Lecture:
Greg Bothun’s Cosmology Book
11/11/03
Prof. Lynn Cominsky