SL applications III

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Cosmography with Lens Time Delays

lecture5

  • Motivation: [10m; RT 10m]
    • What do we want to learn (dark energy, neutrinos)
    • Isn’t distance ladder + CMB enough
  • Brief review of simple theory: [10m; RT 20m]
    • Fermat’s principle
    • Time delay surface
    • Angular Diameter Distances
    • External Convergence vs mass-sheet degeneracy
  • Doing it in practice
    • Measuring time-delays. Without noise: cross-correlate and bootstrap (Basic ideas; Pelt et al) [10m; RT 30m]
    • Astrophysical Noise: microlensing in optical, extrinsic variability in radio. Need for more than one component in lightcurve (Kochanek’s method) [10m; RT 40m]


BREAK #1: DISCUSS WAYS OF DERIVING GOOD FUNCTIONAL FORMS FOR INFERENTIAL ANALYSIS OF LENSED QUASAR LIGHTCURVES. INTRINSIC VARIABILITY? MICROLENSING? [10m, RT 50m] Where to look for clues, papers on proposed physical mechanisms. Physical processes of emission and magnification: stochastic model of AGN, lens model-based approach to microlensing (libraries of simulated curves). What will stop the ML components absorbing all the signal?


  • Building a mass model (Koopmans et al. 2003; Suyu et al. 2010), checking for perturbations (satellites!) [5m; RT 45]
  • Astrophysical “noise”: e.g. dust (Suyu et al. 2010) [5m; RT 50m]
  • Breaking degenearcies (Treu & Koopmans 2002; Suyu et al. 2010): density profile slope - H0 - kappax. Information from arc width, stellar dynamics. [10; RT 60m]
  • Line of sight contamination and the Hilbert method. [10 m; RT 70m]
    • Proxies for kappax: number counts? Reconstruct lightcone? Use of simulations

BREAK #2 TIME DELAY LENS COSMOGRAPHY WILL SOON BECOME SYSTEMATICS LIMITED (WHEN A FEW MORE SYSTEMS ARE COMBINED). HOW CAN THESE SYSTEMATIC ERRORS BE INVESTIGATED? Discussion: realistic simulated systems, parameter recovery under working assumptions to check for bias: this gets the known unknowns. Then: parallel analysis pipelines, comparison tests. Blind analysis enforces systematic error checking and avoids unconscious experimenter bias. Combination with other cosmological probes: gets at systematics *first* and subtle new physics second... [10m; RT 80m]

  • Results and comparison with other methods. [10m; RT 90]

HW: TBD

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