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Peculiar velocity: a window to the dark universe

Peculiar velocity: a window to the dark universe. 张鹏杰 （Zhang, Pengjie) 中国科学院上海天文台 Shanghai Astronomical Observatory Chinese Academy of Science. Based on ZPJ, Michele Liguori, Rachel Bean & Scott Dodelson, 2007, PRL ZPJ & Xuelei Chen, 2008, PRD Bhuvnesh Jain & ZPJ, 2008, PRD

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Peculiar velocity: a window to the dark universe

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  1. Peculiar velocity: a window to the dark universe 张鹏杰（Zhang, Pengjie) 中国科学院上海天文台 Shanghai Astronomical Observatory Chinese Academy of Science Based on ZPJ, Michele Liguori, Rachel Bean & Scott Dodelson, 2007, PRL ZPJ & Xuelei Chen, 2008, PRD Bhuvnesh Jain & ZPJ, 2008, PRD ZPJ, Hume Feldman, Roman Juszkiewicz, Albert Stebbins, 2008, MNRAS ZPJ, 2008, arxiv: 0802. ZPJ, Rachel Bean, Michele Liguori, & Scott Dodelson, 2008, arxiv:0809. KIAS cosmology 2008

  2. The dark universe The visible world Dark energy? Dark matter? Modified gravity? KIAS cosmology 2008

  3. Windows to the dark universe 21cm Soon to detect KIAS cosmology 2008

  4. We are able to put everything together to reconstruct the elephant! CMB lensing peculiar velocity the dark universe SNe Ia BAO cluster abundance KIAS cosmology 2008

  5. The dark energy task force recommends four • probes of the expansion: SN and BAO • probes of structure growth: weak lensing and cluster abundance Peculiar velocity as the fifth!! Figure of merit for stage IV space projects KIAS cosmology 2008

  6. Matter distribution in our universe is inhomogeneous • Gravitational attraction arising from inhomogeneity perturbs galaxies and causes deviation from the Hubble flow v=Hr v=Hr v v peculiar velocity r r KIAS cosmology 2008

  7. What makes peculiar velocity special and important to probe the dark universe? • At scales larger than galaxy clusters, only respond to gravity • In linear regime, honest tracer of matter distribution • Necessary for the complete phase-space description of the universe KIAS cosmology 2008

  8. Early applications of peculiar velocity: (1) A brave new world with gigantic structures Shapely concentration • GREAT attractor(s), with far more mass than expected, must exist in order to pull the Milky way at ～600 km/s with respect to CMB • Such gigantic structures should be no coincidence, if we believe in the cosmological principle Great attractor KIAS cosmology 2008

  9. Early applications of peculiar velocity: (2) road to the standard LCDM cosmology • Largely based on peculiar velocity measurements of local and nearby galaxies, some cosmologists (e.g. Jim Peebles) argued that the the cosmological constant may exist and account for ~80% of the energy budget of the universe, in early 80s. KIAS cosmology 2008

  10. How to measure peculiar velocity?Traditional method Error increases linearly with distance. Can not apply to cosmological distances Measure the recession velocity from the redshift v=Hr v Subtract the Hubble flow to obtain the peculiar velocity r Measure the distance through FP,TF,FJ,SN, etc. KIAS cosmology 2008

  11. New probes of large scale peculiar velocity which do not rely on distance indicators These new probes of large scale peculiar velocity do not rely on subtracting the Hubble flow, so are applicable to z~1 • Redshift distortion (bonus of BAO surveys) • The kinetic Sunyaev Zel'dovich effect of galaxy clusters • Type Ia supernovae at z<~0.5 KIAS cosmology 2008

  12. Redshift distortion and cosmology Kaiser effect induced by large scale coherent infall Finger of God induced by small scale random motion Peacock et al. 2001 KIAS cosmology 2008

  13. A sensitive measure of gravity • Spectroscopic redshift surveys • Measure beta from the anisotropy • Measure galaxy bias • Obtain f Current measurements Guzzo et al. 2008 Acquaviva et al. 2008 KIAS cosmology 2008

  14. BAO surveys (Refer to the WiggleZ talk) are reshaping the field of redshift distortion measurement!(1) the expansion from BAO and(2) the growth rate from redshift distortion BAO • RD helps to improve dark energy constraints • However, the improvement • is not significant for future big surveys • Because if smooth dark energy, BAO and RD basically probes the same H(z) BAO+RD Amendola, Quercellini &Giallongo 2004 KIAS cosmology 2008

  15. Strong tests on gravity DE and MG can have nearly degenerate H(z) But their structure growth rate can be very different Yun Wang 2007 See also Eric Linder 2007 KIAS cosmology 2008

  16. Testing the consistency relation through spectroscopic redshift surveys BAO+CMB =0 in GR+smooth dark energy Redshift distortion Acquaviva et al. 2008 KIAS cosmology 2008

  17. Physics behind the consistency relation = KIAS cosmology 2008

  18. ZPJ et al. 2007; Amendola et al. 2007 Caldwell et al. 2007; Bertschinger& Zukin. 2008 Also Uzan 2006 Hu & Sawicki 2007 = KIAS cosmology 2008

  19. Testing the (generalized) Poisson Equation ? = from peculiar velocity Gravitational lensing Galaxy redshifts to recover redshift information (2D ->3D) KIAS cosmology 2008

  20. Weak lensing • Cosmic shear • DES, LSST, SNAP, Euclid, SKA, etc. • Cosmic magnification • SKA • Cosmic microwave and 21cm backgrounds • Large scale peculiar velocities (bulk flows) • Galaxy redshift distortion from spectroscopic redshift surveys • Stage III: LAMOST, BOSS, WFMOS, etc. • Stage IV: ADEPT, Euclid, HSHS, SKA, etc. • Other methods (KSZ, SNe Ia.... ) KIAS cosmology 2008

  21. Poisson equation! galaxy-galaxy lensing A discriminating probe of gravity Linear density growth rate f redshift distortion • No dependence on galaxy bias • No dependence on the shape and amplitude • of the matter power spectrum, in the linear regime • Scale independent in LCDM and QCDM, whose amplitude is completely fixed by the expansion rate • Contains smoking guns of modifications in gravity and particle physics • Changes in the amplitude • Violation of the scale independence KIAS cosmology 2008

  22. EG will be measured to 1% level accuracy within two decades • Promising to detect one percent level deviation from general relativity+canonical dark energy model (if systematics can be controlled)! LCDM f(R) DGP MOND ZPJ, Liguori, Bean & Dodelson 2007, PRL KIAS cosmology 2008

  23. One can further construct an estimator of η≡-Φ/ΨLensing: Φ-Ψ; Peculiar velocity: Ψ ? Velocity measurement forecasted for SKA ZPJ et al. 2008b KIAS cosmology 2008

  24. dark energy with anisotropic stress DGP • eta can be measured to 10% accuracy. • Errors in eta is larger than errors in E_G • Even so, eta can have stronger discriminating power, in some cases. • η of DGP differs significantly from that of LCDM. (EG of DGP is very close to that of LCDM.) • eta and E_G are complementary • DGP with high Omeag_m MOND TeVeS ZPJ et al. 2008b SKA forecast KIAS cosmology 2008

  25. Layers of assumptions/approximations e.g. Matsubara 2007 e.g. Tegmark et al. 2002,2004 Scoccimarro 2004 ZPJ et al. 2007, ZPJ 2008 F: Lorentz or Gaussian e.g. Acquaviva et al. 2008 deterministic bias e.g. Peacock et al. 2001; Guzzo et al. 2008; Amendola et al. 2004 Linder 2007; Wang 2007 scale independent galaxy bias • More uncertainties: • Linear evolution • Light cone • distant observer assumption • ..... KIAS cosmology 2008

  26. On real data • Tegmark et al. 2002 on 2dF • Tegmark et al. 2004, on SDSS One can measure the gg,gv,vv power spectra simultaneously. errors (vv)>errors(gv)>errors(gg) KIAS cosmology 2008

  27. Forecast for future surveys the Square Kilometer Array (SKA) as an example SKA, ADEPT, HSHS, Euclid Future surveys can detect (1) stochasticity in galaxy bias (2) scale dependence in galaxy bias We are no longer able to use the usual Kaiser formula. At such stage, more detailed check against current RD model and/or more accurate RD modeling are required Other velocity probes? ZPJ 2008 KIAS cosmology 2008

  28. CMB photon The kinetic Sunyaev Zel'dovich effect of galaxy clusters free electron scattered CMB photon vp: bulk velocity scattering probability Recently, the South Pole Telescope (SPT) has for the first time discovered clusters, through the thermal SZ effect! KIAS cosmology 2008

  29. Allows statistical measurement of vp (vp power spectrum) Measure vp of individual clusters Requires other measurements to infer Mg Thermal SZ to have MgT X-ray to have T Measuring velocity from KSZ Haehnelt & Tegmark 1996; Kashlinsky & Atrio-Barandela 2000; Aghanim et al. 2001; Atrio-Barandela et al. 2004; Holder 2004 Statistical errors>systematical errors ZPJ et al. 2008, MNRAS KIAS cosmology 2008

  30. SNe Ia as cosmic speed censors at intermediate redshift ~0.5 Peculiar velocity causes fluctuations in SNe Ia flux Already allow velocity measurement at z<0.1 At z>0.1, lensing dominates over velocity Measure the 3D power spectrum of SNe Ia flux, in which noise can be significantly suppressed signal (velocity) Noise (lensing) z=0.5 ZPJ & Chen, 2008, PRD KIAS cosmology 2008

  31. Peculiar velocity is indispensable for ultimate discrimination between dark energy and modified gravity One necessary condition for DE to mimic MG If 3 or more independent LSS variables can be measured, modified gravity models can be unambiguously discriminated from DE/DM Weak lensing Peculiar velocity ...... Bhuvnesh Jain & ZPJ, 2008, PRD KIAS cosmology 2008

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