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Comments and Questions about the Dark Universe

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  1. Comments and Questions about theDark Universe Charling TAO CPPM & Université de la Méditerranée Chamrousse, Dec. 2004 tao@cppm.in2p3.fr

  2. A mysterious Universe WMAP Position 1st peak WT=1.02 +/- 0.02 Cosmic Microwave Background Flat universe Ratio (2/1) peaks WB =0.046 +/- 0.006 Ordinary Matter: 4% 1/3 Dark Matter 2/3 Dark Energy • CMB, + SN, clusters, galaxies redshift surveys, Weak Lensing, … • Concordant LCDM model with Cold Dark MatterandCosmological constant Definition:W=r/rc (rc=10-29 g/cm3)

  3. Outline of the presentation 1) Brief introduction on SN 2) Present SNIa data 3) Determination of cosmological parameters: a concordant or a convergent Universe? 4) « Experimentalist » point of view: SNIa: « 2 s »  effect? Perhaps too early to speak about new physics !?! 5) How can SN results be improved? 6) Need for more theoretical work 7) What about Cosmology tests in laboratories?

  4. Supernovae • Exploding stars  Brightest objects in Universe • Can sometimes be seen by eye rare! 8 recorded in 2000 years • Historical (super) novae • Chinese records 185, 369, 1006 (arabo-persian also), 1054, 1181. • 1054: Crab Nebula (M1) intense radio, X and gamma emission • 1572 (Tycho Brahe),1604 (Kepler) • visible during the day • 1987A LMC : UV, X, radio, visible, + neutrinos !

  5. Historical SN Classification • Type I : absence of hydrogen +Type Ia: presence of ionised Silicium (SiII) +Type Ib: absence of silicium, presence of helium +Type Ic: absence of silicium and helium • Type II: Presence of hydrogen Ha and Hb + Type II normal: domination of hydrogen, presence of helium. IIL (linear) or IIP (plateau) according to Light curves +Type IIb : Dominating presence of helium • Peculiar types

  6. Supernovae: explosions Red giant White dwarf Chandrasekhar mass 1.4 MO Core Collapse SN SNIa : 2 stars (a white dwarf +…)

  7. Interest of SN study • Physics of galaxies: ISM heavy elements and star formation • Physics of stars: explosion at end of star life • Particle Physics: neutrinos properties • Philosophy: We are all star dust • Cosmology: distance indicators (SNIa)

  8. Measuring distances Cosmology: additional a(t) scale factor D(t) = a(t) D(t0) a(t) = a0(1+ H0t -1/2 q0 (H0t)2 + …) SN 1996 H0 = Hubble parameter measures the expansion rate of the Universe H0= (.a/a)0 = 100 h km/s/Mpc , h= 0.72 +/- 0.05 (?) q0 = deceleration parameter A Universe with only matter is expected to decelerate

  9. The Hubble diagram with SNIa Less luminous/z => Accelerated expansion less matter or more dark energy Too luminous/z => Slowed down expansion => deceleration More matter, less dark energy Absolute magnitude m(z) = M + 5 log (DL(z,WM,WL))-5log(H0)+25

  10. The “classical” SN observation method A 3 steps method: • Discovery: subtraction from a reference image. • Supernova type identification and redshift measurement • Photometric follow-up: light curve spectrum Final analysis: Hubble diagram.

  11. SN are not exact standard candles! The light of SNIa explosions can be followed up for several weeks with telescopes

  12. Different standardisation methods Before:mB After, eg, stretch correction: mBcor = mB – a (s-1) Different standardisation methods :stretch (SCP), MLC2k2 (HiZ), Dm15, ...

  13. The « classical » method data analysis physics galaxy magnitude z(redshift) Images Hubble + identification. Spectra Ia

  14. Fit cosmological parameters • From Hubble diagram, fit models • Determine dark energy parametersWL, or (WX, w, w’)and matter densityWM mag z 1

  15. SNIa • Search for light curves by photometry • Identification of SNIa by spectrometry SURPRISE: acceleration!!! q0 negative W = r(t)/rc(t) = WM+ WL • = 1- Wk L = L/3H02 q0= 1/2 WM- WL < 0 z

  16. 2) SN Ia : the present status a selection by Riess et al,astro-ph 0402512 16 new SN Ia with HST(GOOD ACS Treasury program) 6 / 7 existing with z >1.25 + Compilation (Tonry et al. 2003): 172 with changes from… * Knop et al, 2003, SCP : 11 new 0.4 < z < 0.85 reanalysis of 1999, Perlmutter et al. *15 / original 42 excluded/inaccurate colour measurements and uncertain classification * 6 /42 and 5/11: fail « strict  SNIA » sample cut * Barris et al, 2003, HZT: 22 new:varying degrees of completeness on photometry and spectroscopy records * Blakesly et al, 2003 : 2 with ACS on HST • + Low z : 0.01 < z < 0.15 • Calan-Tololo (Hamuy et al., 1996) : 29 • CfA I (Riess et al. 1999): 22 • CfA II (Jha et al, 2004b): 44

  17. SN Ia 2004 : Riess et al, astro-ph 0402512 183 SNIa selected  Gold set of 157 SN Ia WM=0.29 WL=0.71 Prior: Flat Universe But also non concordant models Fits well the concordance model : c2= 178 /157 SNe Ia

  18. Riess et al. (fit quality)

  19. Determination of Cosmological parameters w=p/r w= w0+w’ z Riess et al, astro-ph 0402512

  20. Recent phenomenological work on SNIa Collaboration CPT/CPPM Virey, Ealet, Tao, Tilquin, Bonissent, Fouchez, Taxil astro-ph/0407452 Simulation and analysis tool: Kosmoshow developed in IDL by André Tilquin (CPPM) marwww.in2p3.fr/~renoir/Kosmoshow.html

  21. Example of possible bias: large w1 4-fit Ms, WM, w0 , w1 3-fit, Ms, WM, w0 • Suggestion Maor et al... • w0F=-0.7 • w1F= 0.8 • WM= 0.3 Beware of fitting method !!! Bias from the time evolution of the equation of state astro-ph/0403285, Virey et al. Quantitative analysis of the bias on the cosmological parameters from the fitting procedure,ie, assuming a constant w, when it is not! With present statistics, can be ignored Not the case with larger samples!

  22. Riess 2004, gold sample Riess Fit with no prior LCDM concordant model

  23. Riess et al. SNIa data: results for different fits (157 SN Ia « gold sample »  Riess et al., astro-ph/040251) w = p/r = w0+ w1z Results Riess et al… • SN data seem to prefer larger Wm • Instability of results with fits • Errors on w1 are ”small” only if Wm ~ 0.3

  24. 3) Reanalysis of Riess et al. SNIa data A concordant or a converging Universe ? Virey et al., astro-ph 0407452 • With prior WM = 0.27 +/- 0.04, always LCDM (ie w=-1) reconstructed, even with different assumptions in simulations , eg, WM = 0.48 , w=/=-1 •  LCDM convergent model !?! • Without flat prior, NO strong constraints from SNIa • Prior: Flat Universe , but no prior on WM • SNIa  WM = 0.48 preferred value Is WM = 0.27 +/- 0.04 ???

  25. Many determinations of WM Riess et al., astro-ph/0402512 SN WM = 0.27 +/- 0.04 X Freedman and Turner, Rev.Mod.Phys. (astro-ph/0308418) WM = 0.29 +/- 0.04 • WMAP: CMB Bennett et al., 2003 ApJS, 148, 1 with h=0.71 +/- 0.05  0.27 +/- 0.04 Spergel et al. 2003 ApJS, 148, 175 • CMB alone WM h2 = 0.14 +/- 0.02  0.27 +/- 0.10 • CMB + 2dFGRS WMh2 = 0.134 +/- 0.006 with h=0.72 +/- 0.05 0.26 +/- 0.04 • 2dFGRS Hawkins et al., astro-ph/0212375 MNRAS, only bias Tegmark et al. astro-ph/0310725 3D power spectrum of galaxies from SDSS • astro-ph/0310723 Cosmological parameters from SDSS andWMAP, • Clusters, Weak Lensing, etc…. N. Bahcall et al. Comparison M/L data/simulationWM = 0.16 +/-0.05 S. Vauclair et al. XMM X-ray clustersWM > 0.85

  26. WMAP cosmological parameters (Table I) • LCDM, ie, flat Universe and equation of state w =p/r = cte (= -1) • Measures Wm h2 and Wb h2  fb = Wb/Wm = 0.17 +/-0.02

  27. !!!! WMAP note !!!!! in Spergel et al., 2003 ApJS, 148, 175 • WM = 0.47, w=-0.5 and h=0.57 => identical power spectrum • solution excluded for 3 reasons: • 1) h=0.57 2s from HST 2) worse fit SNIa results 3) poor fit 2dFGRS galaxy power spectrum surveys Blanchard et al. controversial

  28. 2dfGRS: use of CMB prior

  29. Tegmark et al. astro-ph/0310723 SDSS galaxies power spectrum WM=0.4 h=0.72 =0.5 h=0.56 Baryon fraction • Indication for • Systematics • not cste w? • ? WMAP LCDM h WM

  30. Precision cosmology? Not Just Yet Bridle et al.Science 299(2003) 1532astro-ph 0303180

  31. Bridle et al.

  32. SNIa: fits with weak priorsWM = 0.30 +/- 0.2 Virey, Ealet, Tao, Tilquin, Bonissent, Fouchez, Taxil astro-ph/0407452 • ~ no prior onWM(flat Universe), eg,WM < 0.60 • other solutions still possible : even decelerating Universes Quintessence Phantom

  33. SN data interpretation needs more precise determinations ofWMor combination with other data Tools existing for each observationeg, CMB: CMBFAST, etc… SNIa: Kosmoshow, Y. Wang, … Weak Lensing, Clusters, … Extraction of cosmological parameters using « priors» on other data Tools needed for combined analysis Attempts: Tegmark & Wang, Corasaniti et al., Padmanabhan et al.,… For different models, eg, with variable w

  34. Combined SN, CMB, WL constraints on equation of state 10% measurement Upadhye , Ishak and Steinhardt, astro-ph 0411803 Future constraints SNAP/JDEM + Planck

  35. Dark Energy and Weak Lensing w is measurable by WL power spectrum But degeneracy between w, M,8 and  Hui 1999, Benabed & Bernardeau 2001, Huterer 2001, Hu 2000, Munshi & Wang 2002

  36. “Weak gravitational Lensing” Background image distorsions by foreground matter Without lensing lensing effect

  37. Weak Lensing Distortion Matrix : • Direct measurement of mass distribution in the universe, • Other methods measure light distributions

  38. “Weak Lensing”: principle Distortion Matrix : Convergence: Shear: Critical surface density: Weak lensing regime :  << 1 (linear approximation) Measure shear  and solve for projected mass 

  39. 4) A closer look at SN measurements

  40. Spectroscopy when possible • SN Ia Identification Spectrum structure • Redshift z measurement From position of identified lines from spectra SN and/or underlying galaxy

  41. Simulation of a SN Ia spectrum at z0,5 With Spectra Main stamp of the SNe Ia: Si II at 6150 Å (supernova rest frame): Hardly observable beyond z > 0.4-0.5. Otherwise, search for features in the range 3500-5500 Å (supernova rest frame): Ca H&K, SiII at 4100 Å, SII, … Ca H&K SiII 4100 Supernovæ identification observed at VLT (SNLS)

  42. SNIa sample contamination Need strict selection criteria But reduces statistics !

  43. Atmospheric transmission (ground) Reduced efficiency Not homogeneous filters Redshift dependent !!! Reduction of transmission in visible Absorption water & O2 reduce visibility in IR

  44. Atmospheric emission

  45. Spectroscopy : Need to subtract galaxy

  46. Systematic effects Extragalactic environment local Supernova environment reduction/correlations SNIa contamination Selection bias Inter calibration filters Normal Dust absorption Lensing Grey Dust SN evolution

  47. Systematic effects Observational problems Standardisation method Light curve fitting Heterogeneity of SN data SNIa identification Subtractions Calibrations Atmospheric corrections K-corrections Selection bias • Astrophysical problems • SN evolution • Internal extinction not negligible in spiral galaxies • Corrections for peculiar velocity effects • Grey dust • Lensing • Rowan-Robinson astro-ph/021034 • Perlmutter & Schmidt 0303428

  48. SN Ia photometry needs many corrections mag light curve - Atmospheric observational corrections - Light Curves measured in SN reference frame  in local reference frame - Galactic extinction correction NOT ALL VERY PRECISE OR WELL UNDERSTOOD!, YET!

  49. Precision on the magnitude at the maximum Stretch uncorrected Stretch corrected Precision on the magnitude dominated by intrinsic dispersion: dmint 0.15

  50. Knop et al (2003) light curves