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The Lure of the Dark and Mysterious: Observational cosmology at UIUC

• Overview of Cosmology • The Connection to Particle Physics • Two UIUC Projects. Thanks to Joe Mohr and Robert Brunner; and DES & LSST collaborators. The Lure of the Dark and Mysterious: Observational cosmology at UIUC. The History of the Universe (Compressed by 10 16 ).

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The Lure of the Dark and Mysterious: Observational cosmology at UIUC

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  1. • Overview of Cosmology • The Connection to Particle Physics • Two UIUC Projects Thanks to Joe Mohr and Robert Brunner; and DES & LSST collaborators. The Lure of the Dark and Mysterious: Observational cosmology at UIUC

  2. The History of the Universe (Compressed by 1016) • Big Bang (Early Universe was hot) • Small primordial fluctuations (inflation?) • Perturbations grow (stars, galaxies, bugs).

  3. The “scale factor”, a(t) increases with time. a0 is its value now (t = t0). How to Measure Time We don’t measure time directly, only redshift. Flat FRW cosmology “Equation of state” How a(t) is calculated: •Nonrelativistic matter:w = 0 ra-3at 2/3 •Relativistic matter:w = 1/3 ra-4at 1/2 •Dark energy:w = -1(?)r=r0ae ±Lt Matter-DE equality was at z ~ 0.32, about 3.5 Gy ago.

  4. Cosmological Phenomenology What is observed (partial list) •Primordial chemical abundanceProbes z ~ 1010(when T ~ 0.1 MeV). •Cosmic microvave background (CMB)Probes z ~ 1100 (±70, when T ~ 0.3 eV). •Galaxy and cluster formationProbes z ≤ 10 There is little direct information about the “dark ages,” (10 < z < 1100).

  5. Cosmological Parameters Measurements are strongly correlated. •H(t) Expansion rate, . H2(z) = H20 [ m (1+z)3 + R (1+z)4 + L (1+z)3(1+w) + (-1) (1+z)2 ]Critical density, rc = 3H2/8pG. •W Total energy density(divided by rc). Determines the geometry (open/closed).Wb,Wm,WL, etc. Component densities. •n P(k) k n. (Inflation predicts n  1.) •s8 Density amplitude at k ~ 2p/(8 Mpc). •tOptical depth since z = 1088. •w,w’ “Equation of state” of DE.

  6. Density Perturbations The universe is not quite homogeneous •What is the origin of fluctuations? •Can we understand their evolution? Power spectra: •Expansion of Dx(q,f) in terms of Ylm. l is converted to k, if distance is known. •x is any quantity on the sky(e.g., CMB temperature, galaxy density, etc.) •3-D spectra are just beginning to be done (by, e.g., SDSS).

  7. Peak positions depend on Wtot Relative peak heights depend on Wb Hinshaw, et al. Astrophys.J.Suppl. 148, 135 (2003) Cosmic Microwave Background The primary result of CMB experiments is the spectrum of density fluctuations when z ~ 1100 (t ~ 375 ky AB). Two measurements: •DT(gravitational potential at source) •Polarization (quadrupole moment of r(q,f)) Dr/r ~ 10-5, then. These perturbations grew with time, But not fast enough to make stars soon. Stars began to form at z ~ 10-20, before galaxies. The distance scale for star formation is much smaller (larger k) The primordial spectrum is kn, where n ~ 1. Foreground matter distorts CMB (a problem and an opportunity).(e.g., Sachs-Wolfe & Sunyaev-Zeldovich effects)

  8. Greist & Kamionkowski Physics Reports333-334, 167(2000) • Baryonic matter dissipates and forms a disk. • Noninteracting matter forms a halo. Isothermal: r(r)  r -2 . • If  only visible matter, one expects v(r) r -1 for r > rdisk. • One observes v(r) r 0, consistent with an isothermal halo. Equilibrium density Noninteracting CDM may predict too large a density in the core: Decoupling Discrepancy Models with strong interactions may explain this. • Spergel & Steinhardt, PRL84, 376 (2000) • Wandelt, et al., astro-ph/0006344 Tyson, et al., ApJL, 498, L107 (1998) Dark Matter Is the dark matter composed of weakly interacting particles? (supersymmetry) •The density is about right. •The shape of galactic halos is about right. •Does the dark matter self-interact?

  9. (Wm,WL) (0.25,0.75) (0.25,0.0) (1.0,0.0) Knop, et al., ApJ, 598, 102(2003) dimmer Dark Energy The Cosmological Constant? The expansion is accelerating (ä > 0). This means w ≤ -1/3, or WL > Wm/2. At a given z, a SN is dimmer if ä > 0, because it is farther than if ä = 0. ä 2WL - Wm Possibilities: • Cosmological constant, L. w = -1 • Dynamics (e.g., quintessence)w(a) ~ w0 + w’0 (a-a0) Wang & Tegmark, astro-ph/0403292

  10. mn = 0 mn = 4 eV Verde, et al., ApJ.Suppl. 148,195 (2003) Hu, Eisenstein, & Tegmark PRL 80, 5255 (1998) Neutrinos Neutrino mass has cosmological effects. • At least one neutrino has mn 0.04 eV. •kT0 = 2.310-4 eV, so one n has been nonrelativistic since at least z ~ 200. • Massive neutrinos contribute to structure, but only on large distance scales (knrmn1/2). • Amplitude of contribution Smn. • Present limit: Smn ≤ 0.7 eV (statistics limited).Non-zero result (2.5 s) claimed by Allen, Schmidt, & Bridle, MNRAS346, 59 (2003).

  11. Two Cosmology Projects at UIUC HEP, Astronomy, NCSA Dark Energy Survey (DES) •Upgrade an existing 4 m telescope. •Deeper (higher z) than SDSS, but half the solid angle. •Data in 2008. Large Synoptic Survey Telescope (LSST) •Build a new 8.4 m telescope. •Deeper than DES, and half the sky. (x2 SDSS) •Data in 2012.

  12. Dark Energy DES & LSST will measure DE four ways Measure the z dependence of: •Galaxy cluster distributions •Weak lensing(another way to measure clusters) •Galaxy angular power spectrum •Supernova brightness The first three methods measure the evolution of structure. Supernovas probe H(z).

  13. Dark Energy Survey UIUC, Fermilab, Chicago, LBNL, CTIO The Device: • An upgrade to the existing “Blanco” 4 m telescope at CTIO. • Build a new 500 Mpixel CCD focal plane. • Use ~ 60 2k4k SNAP prototype CCDs. Some parameters: • 2.1° diameter field of view • 45 MBps data rate (no trigger). • ~ 1 PB data set • 600 nights (4 years) • Cost ~ $15M Critical path is CCD acquisition and testing.

  14. Dark Energy constraints from DES clusters The Sunyaev-Zeldovich effect: As CMB photons pass through ionized matter, scattering blueshifts the spectrum nonthermally. This measures the integrated density along the line of sight. WMAP SPT+DES SNAP flat Zeldovich & Sunyaev, Astrophys. Space Sci.4, 301 (1969) Note the correlated errors. Galaxy Cluster Distributions The Initial motivation for DES was optical follow-up to the South Pole Telescope (SPT). • SPT uses S-Z to measures galaxy clusters, but S-Z does not determine redshifts. • DES will measure cluster z’s by surveying the same sky. • Cluster formation rate is sensitive to DE. Data set: • 30,000 clusters and 3108 galaxies • 5000 deg2 (12% of the sky). • 2000 supernovas for z < 0.8. • Galaxy z 1.1, sz ~ 0.03 (photometric).

  15. Weak Gravitational Lensing Observational issues: • Galaxies aren’t round. Statistical analysis. The more galaxies, the better. • Small lens mass  small shear. Must control systematics. • Best sensitivity requires source galaxies at twice the distance. DES will see sources to z ~ 1.1. DES result, if: • 20 gal/arcmin2 • PSF = 0.9 arcsec Hu & Jain, astro-ph/0312395

  16. Szalay, et al., ApJ, 591, 1 (2003) CMB (before WMAP) with LSS Galaxy Angular Power Spectrum We have not completed our analysis, but can scale from published SDSS results (~ 6% of their final data set). • They see 8106 galaxies, will have 1.3108. DES will have ~ 3108. • Their z is <~ 0.5; DES to z ~ 1.1. Observational issue: • We only measure the visible matter, but some parameters aren’t sensitive. • “Bias” does not seem to be a serious problem on large distance scales (where only gravity matters). We think, Smn limit  0.15 eV (statistics only).

  17. Supernovae About 10% of DES time will be spent repeatedly scanning 40 deg2 of sky to find ~1800 Sne (z < ~ 0.8) and measure their light curves. This will be the largest SN sample before LSST & SNAP. Redshift uncertainty will be the largest source of error, so accurate WL will require spectroscopic follow-up. Note the parameter correlations. Assuming Spectroscopic follow-up

  18. The LBT 8.4 m primary mirror LSST DOE groups: SLAC, LLNL, BNL, UIUC, Harvard This will be a new telescope, designed for the science. Large aperture & fast optics Three mirrors, 8.4 m primary f1.25 optics

  19. A 10 s exposure every 12 s. 3 GBps peak data rate 20 TB per night 140 Tflops of real time processing 20 PB image database after 5 yearsImmediate data release (for Sne) Cost: ~ $200M (half is the focal plane + DAQ, the DOE part) 2kx2k, 10µm x 10µm 2.8 x 109 pixels Comparable to LHC • Illustration of a possible detector layout: • 14 “rafts” of 50 2kx2k devices each = 700 devices in focal plane • Det. area ~2800 cm2 , eq. to ~60 cm dia circle, or ~8.5 sq. degrees • ~ 2.8 x 109 pixels LSST DOE groups: SLAC, LLNL, BNL, UIUC, Harvard This will be a new telescope, designed for the science. 60 cm diameter focal plane to image 8.6 deg2 2.8109 pixels (smaller pixels than DES - better resolution)

  20. LSST The survey: (I’m ignoring lots of features) •5-band survey: 400 - 1000 nm (similar to DES) •Sky area covered: 18,000 deg2(~40% of sky, 3x DES) •Limiting magnitude: 26.7 AB mag 10s (2 mag deeper than DES, 5 deeper than SDSS) •Source density: 60 galaxies/sq.arcmin (3-4x DES)

  21. LSST SDSS DES LSST Why a large, fast camera is important. Limiting magnitude: 26.7 AB mag @ 10s 2 mag deeper than DES, 5 deeper than SDSS

  22. LSST What we get: (I’m ignoring lots of things) •3 billion galaxies (10x DES) •250,000 Sne / year 14,000 with dense follow-upz  1 covers the critical region for w & w’.Allows searches for SN model systematics •60 galaxies/sq.arcmin (3-4x DES)

  23. Smn 0.02 Confront the theory! LSST Science payoff: (I’m ignoring lots of things) •sw = 0.02 • sw’ = 0.05 •sWm = 0.09 • sWL = 0.06 Weak lensing clusters Supernovae (no priors)

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