1 / 22

Current Observational Constraints on Dark Energy

Current Observational Constraints on Dark Energy. Chicago, December 2001 Wendy Freedman Carnegie Observatories, Pasadena CA. Current Observational / Experimental Questions. What is the nature of dark matter? Is the universe accelerating? What is the nature

blake
Download Presentation

Current Observational Constraints on Dark Energy

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Current ObservationalConstraints on Dark Energy Chicago, December 2001 Wendy Freedman Carnegie Observatories, Pasadena CA

  2. Current Observational /Experimental Questions • What is the nature • of dark matter? • Is the universe • accelerating? • What is the nature • of dark energy?

  3. Current Evidence for Dark Energy 1. Two independent teams studying type Ia supernovae at high z: Riess et al. (1998); Perlmutter et al. (1999) 2. Flat universe (CMB anisotropies) +Low matter density (several independent measurements) = Missing energy component 0.7 = 1.0 – 0.3

  4. Tests for Dark Energy • Evidence for acceleration (SNIa, SZ) • CMB anisotropies and W0 = 1 • PLUS • Matter density estimates:Wm~ 0.3, LSS • Weak lensing, strong lensing, galaxy counts, • angular diameter (Alcock-Paczynski) tests • Direct measure of the expansion rate

  5. Dark Energy (Wx) • characterize by equation of state w = P(z) / r(z) • w = -1 for a cosmological constant • can be time dependent need observations over a range of redshifts

  6. Evidence for Acceleration Type Ia supernovae • Riess et al. 1998 • Perlmutter et al. 1999 Advantages: • small dispersion • single objects (simpler than galaxies) • can be observed over wide z range • Challenges: • dust (grey dust) • chemical composition • evolution • photometric calibration • environmental differences Wm = 0.3, WL=0.7

  7. Evidence for Acceleration (cont’d) Perlmutter et al. 1999

  8. Evidence for Acceleration (cont’d) • Riess et al. (2001) SN 1997ff • NICMOS serendipitous z = 1.7

  9. Wm Wm~ 0.3 Galaxy kinematics Cluster baryons Current evidence: • fb ~ 10-20% • Wb h2 = 0.02 • Wm ~ 0.3-0.4 Lensing X-ray gas

  10. W0 DASI: Pryke et al. (2001) Boomerang: Netterfield et al. (2001) W0 = 1.03 0.06 W0 = 1.04 0.06 • For same matter content, very different geometryallowed • CMB measurements give no information w(z) • To break degeneracies: H0, galaxy power spectrum, • weak lensing (Hu, Huterer, Turner)

  11. CMB and Supernovae • de Bernardis et al (2001) • Boomerang + SNIa • orthogonal constraints Wm= 0.31 0.13 WL = 0.71 0.11

  12. Combining Constraints CMB & LSS Perlmutter, Turner & White Phys. Rev. Lett. (1999) Combined constraints SNIa • LSS & CMB constraints are • orthogonal to supernova • constraints • sample of ~ 50 supernovae • Peacock & Dodds power • spectrum Huterer & Turner (2001)

  13. Constraining Quintessence Solid line: wq = -0.8 Dashed line: w= -1 A Challenge!!! Best fit: wq = -0.8 Wq= 0.72 Baccigalupi et al. 2001

  14. Combining Constraints Wang et al. (2000) Combined maximum likelihood analysis: -1 < w < -0.6

  15. Gravitational Lens Statistics • Challenges: • Mass distribution of lenses (SIS) • Evolution dependence (merger rates not • well constrained) • Extinction due to dust • Small number statistics Dev et al. (2001): • w < -0.04, Wm < 0.9 at 68%CL • If w = -1, Wm = 0.3 at 68%CL • w = -0.33, Wm = 0.0BEST FIT

  16. Gravitational Lenses Wm=1.0Wm=0.3,open Wm=0.3,flat Kochanek et al. (1999) N(z) versus z Predicted & observed Flat universe, Wm = 0.2 Fundamental plane for lens galaxies Cheng & Krauss (1998)

  17. Age Constraints Huterer & Turner (2001) H0t0 0.25 Wm • consistency check on acceleration • not probe of w(z) 0.35 H0r/H0t0 • H0 = 72 8 km/sec/Mpc (Freedman et al. 2001) • t0 = 13 1.5 Gyr (Chaboyer 2001, Krauss 2000) H0 t0 = 0.93 0.15 w < -0.5 (Huterer & Turner 2001)

  18. The Future

  19. Direct Measure of the Expansion Rate Loeb (1998) : Lyman alpha clouds • ~2 m/s/CENTURY! • not yet feasible • Freedman (2001)

  20. No one said this would be easy… Challenges: • Weak Lensing: • Seeing effects • Shear signal small • Intrinsic alignment • Instrumental noise • Crowding of galaxies • PSF anisotropy • Cosmic variance Supernovae: • Evolution • Dust • Metallicity • Calibration • Environment • K-corrections • Lensing Statistics: • Evolution (merging) • Dust extinction • Velocity dispersions • Model dependence • Numbers small • CMB anisotropies: • Many parameters • Strong degeneracies • No w(z) constraint

  21. No one said this would be easy… Challenges: • Number counts: • Counting statistics • Galaxy evolution • Infall • Velocity errors • Incompleteness • Modeling (N-body) • Cosmic variance Angular Diameters: (correlation functions) • Geometry • Small effect • Peculiar Velocities • Age comparison: • Limits to H0 t0 • Model uncertainties • (stellar evolution) • Zero point calibrations • Dust, metallicity • Cosmic variance • No w(z) information

  22. Summary of Current Observational Constraints • Tantalizing evidence of acceleration in redshift range 0.5 < z < 1.0 • Perhaps first evidence of deceleration at z~1.7 • CMB anisotropies and W0 = 1 strong indication of missing energy component • Consistency checks from numerical simulations, galaxy power spectrum, age • w(z) not yet observationally constrained

More Related