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Supernova cosmology The quest to measure the equation of state of dark energy

Supernova cosmology The quest to measure the equation of state of dark energy. Bruno Leibundgut European Southern Observatory. Outline. Cosmological background Supernovae One-stop shopping for the Hubble constant Acceleration and Dark energy The equation of state parameter of dark energy.

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Supernova cosmology The quest to measure the equation of state of dark energy

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  1. Supernova cosmologyThe quest to measure the equation of state of dark energy Bruno Leibundgut European Southern Observatory

  2. Outline • Cosmological background • Supernovae • One-stop shopping for the Hubble constant • Acceleration and Dark energy • The equation of state parameter of dark energy

  3. Hubble’s Law acceleration jerk/equation of state The expansion of the universe • Luminosity distance in an isotropic, homogeneous universe as a Taylor expansion

  4. Supernova light curve

  5. Based on spectroscopy core collapse in massive stars thermonuclear explosions Supernova classification SN II (H) SN Ib/c (no H/He) Hypernovae/GRBs SN Ia (no H)

  6. Classification

  7. Observing supernovae SINS Suntzeff

  8. Observing supernovae 18 23 28 Virgodistance 33 Suntzeff

  9. Suntzeff gap Observing supernovae 22 24 26 28 z=0.5 30 32

  10. SN 1994D

  11. Krisciunas et al. (2003) SN 2003du European Supernova Collaboration The nearby SNe Ia • excellent coverage for a few objects • fairly complete picture • allows detailed comparisons with models

  12. Germany et al. 2004 The nearby SN Ia sample and Hubble’s law Evidence for good distances

  13. Determining H0 from models • Hubble’s law • Luminosity distance • Ni-Co decay

  14. Hubble law Luminosity distance Arnett’s rule Ni-Co decay and rise time Need bolometric flux at maximum F and the redshift z as observables H0 from the nickel mass α: conversion of nickel energy into radiation (L=αENi) ε(t): energy deposited in the supernova ejecta Stritzinger & Leibundgut (2005)

  15. MPA W7 1M Comparison with models

  16. Acceleration • Originally thought of as deceleration due to the action of gravity in a matter dominated universe

  17. Friedmann cosmology Assumption: homogeneous and isotropic universe Null geodesic in a Friedmann-Robertson-Walker metric:

  18. distance (Mpc) acceleration relative distance redshift Measure acceleration

  19. No Big Bang ΩΛ ΩM Cosmological implication • Empty Universum • Einstein – de Sitter • Lambda-dominatedUniverse • Concordance Cosmology

  20. ???? New Fundamental Physics! What is Dark Energy? G+ f(g) = 8G [ T(matter) + T(new) ] Two philosophically distinct possibilities: • Gravitational effect, e.g. Cosmological Constant, or gravity “leaking” into extra dimensions • A “Vacuum energy” effect, decaying scalar field

  21. The equation of state parameter  • General luminosity distance • with and M= 0 (matter) R=⅓ (radiation) = -1 (cosmological constant)

  22. Current Limit on Dark Energy: w < -0.7 Spergel et. al. 2003 Tonry et. al. 2003 Dark Energy Equation of State 2dF prior

  23. Dark Energy Models Quintessence Gravitational, e.g. R-n with n>0 (Carroll et. al. 2004) Cosmological Constant Exotic! (Carroll et. al. 2003) In general unstable Pair of scalars: “crossing” from w>-1 to w<-1 Physical issues • w > -1 w = -1 w < -1

  24. ESSENCE • World-wide collaboration to find and characterise SNe Ia with 0.2<z<0.8 • Search with CTIO 4m Blanco telescope • Spectroscopy with VLT, Gemini, Keck, Magellan • Goal: Measure distances to 200 SNe Ia with an overall accuracy of 5%  determine ω to 10% overall

  25. ESSENCE spectroscopy Matheson et al. 2005

  26. ESSENCE spectroscopy (cont.)

  27. First two years of ESSENCE spectra Matheson et al. 2005

  28. Spectroscopic study Blondin et al. 2005

  29. And on to a variable ω Ansatz: ω(z)= ω0+ ω’z Riess et al. 2004

  30. Time-dependent w(z) • Maor, Brustein & Steinhardt 2001 Luminosity Distance vs redshift can be degenerate for time-varying ω(z)

  31. SN Projects SN Factory Carnegie SN Project ESSENCE CFHT Legacy Survey Higher-z SN Search (GOODS) SNAP

  32. Four redshift regimes • z<0.05 • Define the characteristics of Type Ia supernovae • Understand the explosion and radiation physics • Determination of H0 • z<0.3 • Explore the systematics of SNe Ia • Establish distance indicator

  33. Four redshift regimes (cont.) • 0.2<z<0.8 • Measure the strength of the cosmic acceleration (dark energy) • z>0.8 • break the degeneracy • measure matter density • All redshifts • Measure details of dark energy

  34. The SN Ia Hubble diagram • powerful tool to • measure the absolute scale of the universeH0 • measure the expansion history (q0) • determine the amount of dark energy • measure the equation of state parameter of dark energy

  35. Caveats • Warning to the theorists: Claims for a measurement of a change of the equation of state parameter ω are exaggerated. Current data accuracy is inadequate for too many free parameters in the analysis.

  36. Summary • Type Ia supernovae appear currently the most promising route to provide a possible answer to what the Dark Energy is. • All redshifts need to be covered • distant SNe Ia alone are useless • nearby SNe Ia are the source of our understanding of the distance indicator

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