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The Sunyaev Zel’dovich effect (2001-present)

Pengjie Zhang Shanghai Jiao Tong University The large scale structure and its cosmological applications. The Sunyaev Zel’dovich effect (2001-present) Missing baryons, dark flow, vacuum decay, bubble collision The thermal and kinetic SZ tomography Weak gravitational lensing (2003-present)

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The Sunyaev Zel’dovich effect (2001-present)

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  1. Pengjie ZhangShanghaiJiaoTongUniversityThelargescalestructureand its cosmological applications • TheSunyaevZel’dovicheffect (2001-present) • Missingbaryons,darkflow,vacuum decay, bubble collision • The thermal and kinetic SZ tomography • Weakgravitationallensing (2003-present) • Systematicsintheory (Born deviation, lens-lens, source-lens (see Yu Yu’s talk on Oct. 11), baryons, etc.) • Systematics in observation and self-calibration (2010) • Self-calibratingphoto-zandintrinsicalignment • Mapping dark matter with cosmic magnification (2005-present) • Not background-foreground cross correlation works in the literature • Redshiftspacedistortion (2007-present) • Theoreticalmodelingandvelocityreconstruction • Velocitystatistics(seemytalk on Oct. 9) • Cosmologicaltestsoffundamental cosmology • GR, the Copernican Principle, origin mechanism, etc. THCA, 2014.10.9

  2. Velocity BiasChallenge/opportunity to peculiar velocity cosmology 张鹏杰ZHANG, Pengjie ZPJ, Zheng & Jing, 2014, arXiv: 1405.7125 Zheng, ZPJ & Jing, 2014a, arXiv: 1409.6809 Zheng, ZPJ & Jing, 2014b, arXiv: 1410.1256 Sampling artifact Velocity bias Hard works are done by Zheng Yi, my student just graduated. THCA, 2014.10.9

  3. Peculiar velocity: a window to the dark universe 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 THCA, 2014.10.9

  4. Peculiarvelocity:unique probe ofcosmology At scales larger than galaxy clusters, directlyprobes gravity(t-tcomponent: In linear regime, honest tracer of matter distribution Necessary for the complete phase-space description of the universe THCA, 2014.10.9

  5. Challenges • However,accuratevelocitymeasurement? In particular at cosmological distance, e.g. z~1? • Conventionalmethod:subtracttheHubbleflowwithdistanceindicators(FP,TF). • E.g.SFI++,6dF(e.g.Johnsonetal.1404.3799) • Statisticalerrorsblowupwithredshift. Onlyapplicableatz<0.1 • Systematicerrors(e.g.6dF,Magoulasetal.1206.0385). • Newmethods • Kinetic Sunyaev Zel’dovich effect: bias from baryon mass • SNe Ia: statistical errors blow up with z; contamination from lensing • Relativisticeffectsingalaxynumberdensity: only detectable at horizon scales(e.g.Yooetal.2011) • Relativisticeffectingalaxysize/flux/magnificationbias: only applicable at low z(e.g.Bonvin,2008. But see ZPJ & Chen 2008) • Redshift space distortion: very promising….

  6. Measure peculiar velocity at cosmological distanceheuristicapproach Peculiarvelocitycan be reconstructed! Notonlytheaveragestatistics,butalsothe3Dfield Realspacepowerspectrum Redshiftspacepowerspectrum Also directly measurable! Directly measurable

  7. Through the anisotropy in the redshift space power spectrum, one can reconstruct the velocity power spectrum Has been applied to real data (Tegmark et al. 2002 on 2dF; Tegmark et al. 2004, on SDSS; etc. ) After layers of approximations,

  8. Oftenfurther compressed into a single number • Will be improved significantly by eBOSS • To 1% by stage IV surveys such as DESI , Euclid and SKA Chuang et al. 1312.4889

  9. Velocity bias or not?Afundamentalprobleminpeculiarvelocitycosmology THCA, 2014.10.9

  10. Velocity bias: potential systematic error • A first order systematic error in cosmology • Have to understand the velocity biasto 1% level accuracy at k~0.1h/Mpc. THCA, 2014.10.9

  11. Peculiar velocity cosmology by default assumes no velocity biasatlargescale: • Environmental effect: halos/galaxies locate at special regions around density peaks. Proto-halos/linearly evolved density peaks (BBKS 1986; Desjacques & Sheth 2010) have velocity bias What would be the velocity bias of halos in simulations? THCA, 2014.10.9

  12. Severe sampling artifactcanbemisinterpretedasa“velocitybias” DM • Naive comparison between the raw measurements of halo velocity and DM velocity gives a apparent bv<1 • Illusion caused by the sampling artifact • Unphysical numerical effect.Butcanbemisinterpretedasa“velocitybias” Halo Yipeng’s P3Msimulation: 1200 Mpc/h, 10243 particles Zheng, ZPJ, Jing, 2014b THCA, 2014.10.9

  13. Detection of the sampling artifact in DM velocity field DM control samples: Randomly select a fraction of DM simulations particles. By construction, the control samples and the FULL sample should have identical velocity. Therefore any difference is the result of sampling artifact. Zheng, ZPJ, Jing, 2014a THCA, 2014.10.9

  14. The sampling artifact Where there is no particle, the velocity is usually non-zero. It can be large. The sampling on the volume weighted velocity field is biased/imperfect The sampling artifact: inevitable for inhomogeneously distributed objects. Severe for sparse populations. Persists for NP, Voronoi and Delaunay tessellation. The sampling and the signal are neither completely uncorrelated nor completely correlated. Hard to correct straightforwardly Can be fully described in the language of the D field (ZPJ, Zheng & Jing, 2014), similar to CMB lensing ? THCA, 2014.10.9

  15. Understanding the sampling artifact Neglect v-D correlation. Including the correlation in D.Not exact. Neglect correlation in D Zheng, ZPJ& Jing, 2014a ZPJ, Zheng & Jing, 2014 • Our model works. • But improvements are needed • Take correlation in D fully into account • Take v-D correlation into account THCA, 2014.10.9

  16. Theory and simulation of the sampling artifact The measured velocity power spectrum The real velocity power spectrum Simulation verification Zheng, ZPJ & Jing, 2014a Theory prediction: ZPJ, Zheng & Jing, 2014 THCA, 2014.10.9

  17. Sampling artifact: theory vs. simulation THCA, 2014.10.9

  18. Raw measurement Step one Correction Step two correction THCA, 2014.10.9

  19. 1. Velocitybiasvanishesatk<0.1h/Mpc. Consolidates peculiar velocity cosmology2. Velocity bias at k>0.1h/Mpc? Poses a challenge THCA, 2014.10.9

  20. For discussions • Needstheoryexplanation • Needsmoreaccuratequantification • Needimprovedunderstandingofthesamplingartifact • Needstoextendtogalaxies(mockcatalog) • Perhaps needs new velocity assignment (e.g. Jun Zhang’s idea) • Cosmologicalapplications • CouldbesmokinggunsofMG • Promisingtestsoftheequivalenceprinciple(ongoingworkwithZhengYi,Yipeng,BaojiuLi & De-Chang Dai) THCA, 2014.10.9

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