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Surveying the Universe

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  1. Surveying the Universe Russell Johnston Dept of Physics and Astronomy University of Glasgow

  2. Edwin Hubble

  3. Hubble measured the shift in colour, or wavelength, of the light from distant galaxies. Galaxy

  4. Hubble measured the shift in colour, or wavelength, of the light from distant galaxies. Galaxy Laboratory

  5. Hubble’s Law: 1929 Distant galaxies are receding from us with a speed proportional to their distance

  6. Spacetime is expanding like the surface of a balloon. As the balloon expands, galaxies are carried farther apart

  7. Although Hubble got the expansion law correct, his measurement of the current rate of expansion was quite wrong, and took many decades to correct.

  8. Measuring the Hubble constant was a key project of the Hubble Space Telescope

  9. More recently we have extended the Hubble diagram to great distances, using e.g. Supernovae…. Region probed by Hubble’s data

  10. Models with different shapes ‘Speeding up’ model ‘Slowing down’ model Hubble’s law for nearby supernovae redshift ….This has led to a remarkable discovery: The expansion of the Universe is speeding up! measure of distance

  11. What is driving the cosmic acceleration?… Dark Energy

  12. AroundGalaxies Orbital velocity (km/s) Distance from the Galaxy Centre (kpc) Typical size of galaxy disk

  13. What we see What we see What is really there.

  14. 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

  15. Marc Davis, John Huchra, Dave Latham, John Tonry • Redshift range: out to z 0.05 The First Redshift Surveys • CfA Survey #1 : 1977 - 1982 • Surveyed a total of 1100 galaxies CfA # 1

  16. Our own Galaxy de Lapparent, Geller, and Huchra (1986), ApJ, 302, L1

  17. Filament Void? Rich cluster

  18. Margaret Geller • Redshift range: out to z 0.05 208 Mpc The First Redshift Surveys • CfA Survey #2 : 1985 -1995 • John Huchra & • Surveyed a total of 18,000 galaxies CfA # 2

  19. Redshift surveys (mid-1980s) 1 Mpc = 3.26 milion light years

  20. 1995 (LAS CAMPANAS) The size of the structures is similar in both samples The largest structures in LCRS are much smaller than the survey size LCRS

  21. Will Saunders, Seb Oliver, Carlos Frenk & Luis Teodoro. The First Redshift Surveys • IRAS PSCz : 1992 – 1996, 15,000 galaxies • Team originally consisted of around 24 members including: Will Sutherland, Steve Maddox, • Catalogued over 83% of the sky - Largest full sky survey.

  22. The Two Degree Field Galaxy Redshift Survey (2dFGRS) • The survey covered two strips : NGP - SGP - • Recovered a total of 245,591 redshifts, 220,000 of which were galaxies out to • Galaxies brighter than Surveys…. The Next Generation • Ran from 1998 to 2003. • Used the multifibre spectrograph on the Anglo Australian Telescope. • Photometry was taken from the APM galaxy catalogue.

  23. 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 Peder Norberg Warrick Couch Shaun Cole

  24. The Two Degree Field Galaxy Redshift Survey (2dFGRS)

  25. The Two Degree Field Galaxy Redshift Survey (2dFGRS)

  26. = 100 Mpc diameter

  27. 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

  28. The Sloan Digital Sky Survey (SDSS)

  29. CfA SDSS

  30. Sloan Digital Sky Survey: The Footprint of the Survey

  31. Area and Size of Redshift Surveys

  32. Galaxies and Cosmology: the Basic Paradigm 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

  33. 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 : Cold dark matter + non-zero cosmological constant

  34. 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 : Cold dark matter + non-zero cosmological constant The Concordance Model

  35. From Lineweaver (1998)

  36. 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’.

  37. 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’. Atoms Cold Dark Matter Dark Energy

  38. 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. Atoms Cold Dark Matter Dark Energy

  39. 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 Atoms Cold Dark Matter Dark Energy

  40. 140 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

  41. 140 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

  42. 140 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

  43. 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

  44. 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