Quasars

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Quasars Cosmology
Quasars and Cosmology
ASTR-1510-01 ASTR-1510-02
Department of Physics, Applied Physics
Astronomy, RPI
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Week 8

• The Large-Scale Structure
• of the Universe
• Jones Lambourne
• Sections 4.4-7
• October 19, 2009
• 300 PM
• Darrin 330

Department of Physics, Applied Physics
Astronomy, RPI
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This Weeks Reading

• Section 4.6 (Describing cosmic structure) is
  rather technical. You are NOT responsible for
  understanding the counts in cells method.

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Outline

• Imaging Galaxy Surveys
• Redshift and Distance
• Redshift Galaxy Surveys
• Distribution of Galaxies
• Distribution of Gas Dark Matter

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Review Structure in the Universe

• The Universe contains different kinds of matter
• dark matter (70 to 90)
• galaxies (less than 10)
• hot gas between the galaxies (10 to 25)
• Matter is NOT distributed smoothly like Jello!
• Tiny quantum fluctuations seeded growth of
  structure.
• Gravity amplified seeds into huge structures.
• Starlight reveals structure of VISIBLE matter
• Stars group to make galaxies (D 100 kpc).
• Galaxies group to make galaxy clusters (D few
  Mpc).
• Do the clusters make bigger structures? TODAY!
• Does this hierarchy go on forever? TODAY!

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The APM Imaging Survey

• A map of about 1/10 of entire sky.
• Each point 1 galaxy. About 2 million in all.
• Holes where bright stars cut out.

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2D Imaging Surveys (like APM)

• Map big patches of sky. (Good)
• Find very faint galaxies. (Good)
• No distances measured. (Not so good)
• Structure does appear.
• But how much of this is just constellations?
• Need 3D information.

APM survey in color1
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Spectral Lines and Redshift, z
galaxy
laboratory
lLAB wavelength of line (lab)
lGAL wavelength of same line (galaxy)
z lGAL/lLAB-1
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Light Wave in a Universe
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Later - Static Universe
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Later Expanding Universe
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Relation to Distance
Hubbles Law
distance
Exact
z

• Hubbles Law (valid for small redshifts, z lt
  0.2)

z H0 d/c

• For larger z relation still exists but not
  straight line.
• Relation depends on which universe you live in.

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Redshift Surveys

• Distance position on sky 3D info. (Good!)
• But spectra require MUCH more data! (Bad!)
• Hubble only got one or two spectra PER YEAR.
• Q How can you get thousands of redshifts?
• A Ask M. Davis, J. Huchra, J. Tonry M.Geller

Prof. Margaret Geller, Harvard U. MacArthur
Fellow.
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Whats The Big Deal?
one square degree
HST 1/20 x 1/20 degree!

• Need 20 x 20 400 images per square degree.
• About 40,000 square degrees on the whole sky.
• Need about 16,000,000 images for whole sky!
• Each image might take hours!
• About 4 billion galaxy spectra to take!

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The CfA Redshift Survey2
more

• 3D map of 6 degree by 130 degree strip on sky.
• About 1,500 galaxy redshifts.
• Distances to about 200 Mpc (zlt0.02).
• Found finger of God and great wall.

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The 2dF Redshift Survey3
more

• 3D map of 2x2 degree square on sky.
• About 250,000 galaxy redshifts in 5 years!
• Distances to about 3,000 Mpc (out to z0.3).

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Sloan Digital Sky Survey (SDSS)5

• mapped ¼ of entire sky!
• 2.5m telescope.
• multi-object (640) spectra
• about 1,000,000 redshifts!
• distances to 800 Mpc
• redshifts to z-0.25

2.5m SDSS telescope
SDSS quasar spectrum, z4.16
multi-object spectrograph
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A Typical Pie Diagram from SDSS5

• each point is 1 galaxy.
• you are at the vertex.
• edge is at z0.3 (approx).
• thats d1,000 Mpc (approx)

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Lots More Surveys!!!
http//www8.nationalacademies.org/astro2010/Detail
FileDisplay.aspx?id208
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What They Found So Far

• Galaxy clusters make superclusters.
• Typical supercluster size D 30-50 Mpc.
• Superclusters DO NOT make bigger structures!!!
• On largest scales (gt 200 Mpc)
• Universe is foamy, spongelike
• huge voids about 60 Mpc in diameter.
• most galaxies on sheets/filaments around voids.
• Universe homogeneous averaged over larger scales.

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The Universe within 1 Billion Light Years4
Zoom
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Rotation Curve of the Solar System
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Galaxy Rotation Curves Dark Matter
Rotation speed vs. Distance from galaxy center
Mass inside radius R vs. Distance from the galaxy
center
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All Galaxies Have Dark Matter Halos!
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Gravitational Lensing Detects All Matter
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An Einstein Ring6
Foreground galaxy (bright spot, center) lenses
distant galaxy (ring).
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Two Einstein Crosses
Each lens galaxies (yellowish) deflects the light
from a distant quasar (blue) imaging it four
times on the sky.
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Gravitational Lensing By Galaxy Clusters
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Cosmic Shear7
Paths of 3 light rays in computer simulation of
filaments clusters. The deflections have been
grossly enhanced (in the real universe the
deflections are very small).
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The lensed galaxies are not round (in the absence
of lensing, that is), but have their own shape.
If the lensing signal is strong enough (left
panel) there is no problem finding the lens.
However,  in the weak lensing region (right
panel)  the galaxies appear to be oriented at
random. However, as the sticks indicate, on
average,  the galaxies are aligned tangentially!
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What Cosmic Shear Tells Us

• This is a new and evolving field of research.
• So the final word is not in yet.
• But it seems that dark matter DOES have same
  structure as visible matter.

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Image Credits
1Copyright S. Maddox, W. Sutherland, G.
Efstathiou J. Loveday, Oxford U. 2V. De
Lapparent, M. Geller J. Hychra, Harvard
Smithsonian Center for Astrophysics 3Anglo
Australian Observatory 4atlasoftheuniverse.com 5Sl
oan Digital Sky Survey 6HST image by J.L. King,
University of Manchester. 7S. Colombi (IAP),
CFHT Team.