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Once and Future Redshift Surveys

Once and Future Redshift Surveys. Matthew Colless Anglo-Australian Observatory. UK National Astronomy Meeting 8 April 2005. Large-Scale Structure in Different Model Universes.

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Once and Future Redshift Surveys

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  1. Once and FutureRedshift Surveys Matthew Colless Anglo-Australian Observatory UK National Astronomy Meeting 8 April 2005

  2. Large-Scale Structure in Different Model Universes • The large-scale structure of the galaxy distribution, on scales from millions to billions of light-years, depends on… • the amounts of the various constituents of the universe (ordinary matter, dark matter, dark energy etc.) • the recipe for how galaxies are formed (when, where, and with what bias relative to the dark matter) 100 million light-years

  3. The million brightest galaxies on the sky The universe in a computer 3-D?

  4. Hubble correctly interpreted this as the isotropic expansion of the universe. E.H. • Hubble’s Law: at low redshift, the recession velocity of a galaxy is proportional to its distance. • Measuring redshifts (recession velocities) gives distances. The Expansion of the Universe • In 1929, Edwin Hubble found that… • all distant galaxies are moving away from our Milky Way galaxy; • the further away they are, the faster they are receding from us.

  5. You are here A redshift survey of a strip of sky is a slice through the 3-D galaxy distribution

  6. CfA Survey ~15000 z’s Las Campanas Redshift Survey ~25000 z’s State of the Art in the mid-1990’s How to do better?

  7. 2dFGRS SDSS Comparison of Redshift Surveys

  8. The 2-degree Field spectrograph AAO technology combining robotics and optical fibres Obtains spectra for 400 galaxies at once 2dF enabled a huge redshift survey

  9. Random fields The 2dF Galaxy Redshift Survey ~250,000 galaxies ~2000 deg2 NGP strip SGP strip

  10. NGP R.A. strip z0.3 You are here SGP R.A. strip The Galaxy

  11. The 2dF Galaxy Redshift Surveymap of 221,000 galaxies

  12. Cosmology by eye! CDM bias #1 SCDM bias #1 Observed CDM bias #2 SCDM bias #2

  13. The Galaxy Power Spectrum • The final galaxy redshift-space power spectrum from full 2dFGRS • The acoustic oscillations (“baryon wiggles”) are detected at the 4 significance level Cole et al. 2005, astro-ph/0501174

  14. Total matter and Hubble constant: Wmh = 0.168±0.016 Baryonic matter fraction: Wb/Wm= 0.185±0.046 Direct from 2dFGRS alone Total matter density: m = 0.2310.021 Cold dark matter density: CDM = 0.1890.020 Baryonic matter density: b = 0.0420.002 2dFGRS and WMAP combined Total matter, dark matter and baryon densities

  15. Wn=0.05 Wn=0.01 Wn=0 Constraints on the neutrino mass P(k) gives an upper limit on the total mass of all n species Best previous bound Wn/Wm< 0.13 Elgaroy et al., 2002, PRL, 89, 061301 2dFGRS: Wn/Wm < 0.13 mn,tot < 1.8 eV (95% confidence) +WMAP: Wn/Wm < 0.05 mn,tot < 0.7 eV (95% confidence)

  16. Cosmology and LSS results from the 2dFGRS • The large-scale structure of the galaxy distribution is precisely determined on size scales from about 1 million light years to about 1 billion light-years • The properties of the galaxy distribution confirm that the large-scale structure grows by gravitational instability…quantum(?) fluctuations emerging from the Big Bang are amplified by gravity to become galaxies, clusters and superclusters • The total density of all matter in the universe is M = 0.230.02 there is only 23% of the matter needed to make the universe flat • The total density in ordinary matter is B = 0.0420.002 baryons are 18% and CDM 82% of the matter in the universe • Neutrinos make up less than 5% of all the matter in the universe the total mass of the 3 neutrino species is less than 0.7 eV

  17. SNe CMB 19% 77%

  18. SNe Hubble Relation • Measure the brightnesses (distances) for many SNe at different redshifts to obtain the Hubble relation • Look for deviations from a simple straight line  out to nearly z~1 the expansion is seen to be accelerating Relative Brightness  Distance Redshift

  19. Hubble Relation for High-Redshift Supernovae • However, using SNe at higher z, we see at first the expansion of the universe accelerating, then at larger distances the expansion decelerating

  20. WMAP 2003

  21. The CMB power spectrum from WMAP

  22.  the geometry of the universe is flat  there is less than the critical density of matter  the expansion of the universe is accelerating  the overall scale (size/age) of the universe Standard Model Cosmic Microwave Background + Large-Scale Structure + Distant Supernovae + HST Key Project

  23. 2dFGRS The State of the Universe • The geometry of the universe is flat (CMB) • Matter makes up 23% of the energy density in the universe (2dFGRS) • The expansion of the universe is accelerating (SNe) • Dark energy makes up 77% of the energy density in the universe (any two of the above)

  24. ? ? ? The Composition of the Universe tot= 1.02  0.02  = 0.77  0.04 DM = 0.19  0.02 B = 0.040.002  < 0.01

  25. The Cosmic Timeline • Hubble constant:H0 = 71  4 km/s/Mpc(HST KP H0= 72  7 km/s/Mpc) • CMB last scattering surface: tCMB = 379  8 kyr • Epoch of Re-ionization:tEoR = 100-400 Myr • Age of the universe today:t0 = 13.7  0.2 Gyr

  26. Dark Matter and Dark Energy • Although we now know the amounts of all the major constituents of the universe we still have two major gaps in our knowledge… What is the dark matter? What is the dark energy?

  27. What more can z-surveys say about dark matter? • Additional information comes from measuring the distances as well as the redshifts to obtain both the galaxy densityandvelocity distributions • Since galaxy velocities are directly produced by gravity from the matter distribution, this jointly constrains both luminous and dark matter

  28. The 6dF Galaxy Survey The AAO’s UK Schmidt Telescope The 6dF fibre spectrograph • The 6dFGS is now mapping the mass & motions in the very local (z<0.1) universe • The survey aims to measure redshifts for a NIR-selected (2MASS) sample of 150,000 galaxies, plus velocities for 15,000 galaxies (10x previous surveys) • Currently 2/3 of southern sky mapped (DR2 next week); complete mid-2005

  29. The 6dFGS map of the local universe

  30. Predicted 6dFGS galaxy power spectrum Effective volume Non-linear regime shot noise/mode Predicted errors

  31. Predicted 6dFGS velocity power spectrum Larger errors reflect smaller size of survey and 1D peculiar velocities Predicted errors

  32. z-onlyz+v 1 contours on pairs of parameters Constraints from joint redshift-velocity survey • For cosmological models specified by: • the power spectrum amplitude and shape (Ag, ) • the redshift-space distortion () • the galaxy-mass correlation (rg) … the errors from the combined redshift and velocity surveys are 1-3% in all four parameters … the velocity survey much improves the joint constraint on  and rg, which are now only relatively weakly correlated Burkey & Taylor (2004)

  33. What can z-surveys say about dark energy? • Is dark energy Einstein’s cosmological constant, or new physics? • The nature of the dark energy affects the geometry of the universe, which can be measured by comparing the structure in the galaxy distribution (specifically, the apparent scale of the acoustic oscillations) at different times. • The geometry of the universe is measured at early times by the CMB, and at late times by the 2dFGRS. • Redshift surveys of ~106 galaxies at intermediate redshifts (say, z~1 and z~3) could map the geometry over the full span of cosmic time and see the transition from a dark matter dominated universe to a dark energy dominated universe.

  34. The Dark Energy Equation of State • The equation of state for dark energy is the ratio of pressure to density as a (potentially evolving) function of redshift, w(z) • For cosmological constant , w-1 and does not change with z • For new physics, this is not the case: w(z) = w0 + w1z +… • Determining w(z), esp. if w0-1 and w10, would be a major step towards understanding the nature of the dark energy • Measuring the geometry of the universe may therefore provide a window on new physics (quantum gravity? string theory?)

  35. Equation of State from Acoustic Oscillations • w(z) requires high-precision versions of the classical cosmological tests, as likely effects on geometry are small • Use the ‘standard rod’ provided by scale of acoustic oscillations in the galaxy power spectrum (‘Doppler peaks’ in CMB)

  36. Ωm Ωm Current constraints on the EoS • Constraints from z-surveys, cluster evolution, BBNS, SNe & CMB • The 95% confidence interval is approximately -1.5<w<-0.8 •  (w=-1) is consistent with all data; Big Rip (w<-1) is possible Allen et al., 2004, MNRAS, 353, 457 2dFGRS 2dFGRS

  37. Redshift Surveys & Dark Energy • Measure acoustic oscillations with redshift surveys of large-scale structure at high redshift: • z~1: 900,000 gals, 1000 deg2 • z~3: 600,000 gals, 150 deg2 • For interesting cases with w10, z-surveys give similar constraints to other methods (e.g. SNe) • Combining methods (LSS, CMB, SNe) increases the precision in measuring both w0 and w1 • Redshift survey method has the advantage that it should be less subject to systematic errors

  38. WFMOS on Gemini/Subaru • WFMOS is ideal for massive surveys of high-redshift galaxies: • 8-metre telescope • 4500 optical fibres • 1.5 degree field of view

  39. Once and Future Redshift Surveys • Wide-field spectroscopy has been, and will continue to be, a very powerful tool for studying large-scale structure and cosmology • Combined with CMB, SNe and other observations, the 2dFGRS and SDSS provide a precise picture of the low-redshift universe • The combined 6dF redshift-velocity survey will provide additional constraints on the relation between luminous and dark matter • Future massive redshift surveys at high redshift with AAOmega, FMOS and WFMOS can trace the evolution of galaxies and large-scale structure, and reveal the nature of the dark energy

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