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Dark Energy, Halo Mass Functions and Lens Statistics

Dark Energy, Halo Mass Functions and Lens Statistics. 채규현 (Kyu-Hyun Chae) 세종대학교 천문우주학과. 1. Dark Energy (DE). Theoretical possibility invoked to explain the observed accelerating expansion of the Universe Alternatively, modified gravity theories

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Dark Energy, Halo Mass Functions and Lens Statistics

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  1. Dark Energy, Halo Mass Functions and Lens Statistics 채규현 (Kyu-Hyun Chae) 세종대학교 천문우주학과

  2. 1. Dark Energy (DE) • Theoretical possibility invoked to explain the observed accelerating expansion of the Universe • Alternatively, modified gravity theories • An evolving dark energy or a cosmological constant? • Whether dark energy evolution crosses (has crossed) the phantom divide line (PDL)? • Present cosmological observational results do not appear to converge.

  3. Consider the following parameterization for the evolution of the DE equation of state (EOS) : (Linder 2003) w0 =-1 & w1 =0 : Einstein’s cosmological constant w0 = present-epoch EOS w0 + w1 = EOS right after the big bang w1 = evolution parameter

  4. Key cosmological factor: Cosmological distances [dL(z), dA(z)] depend on this factor.

  5. 2. Recent Constraints on DE Evolution Type Ia supernovae observations [in particular, Gold data set, Supernova Legacy Survey (SNLS) data set, ESSENCE data set]: luminosity distance-redshift relation [inv. ], WMAP 3-year results: angular-diameter distance of the sound horizon at zdec [inv. ] SDSS luminous red galaxies: baryonic acoustic-peak oscillations (BAO) [inv. ] …..

  6. Nesseris & Perivolaropoulos (2007)

  7. Wu & Yu (2007)

  8. Based on current results: DE Evolving or Not? - The current results are inconclusive: Different data sets produce different results. - Some results suggest an evolving DE that has only recently crossed the PDL. - Further independent cosmological tests are warranted.

  9. 3. Lens Statistics Test of DE Multiple-imaging (strong lensing) probability: n(z): number density, e.g. s: cross section. B: magnification bias Differential probability:

  10. For the distribution of the number density, we use the velocity dispersion function dn/dσ of early-type galaxies based on the SDSS DR5 data (Choi, Park, & Vogeley 2007). • For the lensing potential, we use the singular isothermal ellipsoid mass model. • Use CLASS + other radio-selected lens sample of 26 lenses.

  11. Ωm0=0.2 Ωm0=0.25

  12. Strong Lensing appears to slightly favor an evolving DE EOS that has crossed the PDL at a recent epoch! Larger data sets are required for improving precision (e.g. SKA).

  13. 4. Dark Halo vs Galaxy Theory: N-body simulations and analytical models halo mass functions & mass profiles baryonic physics: cooling, star formation & feedback, … galaxy velocity functions & modified mass profiles Observations: rotation velocities, gravitational lensing, etc

  14. (Theory) (observation) (spectroscopic survey; strong lensing) (simulation) (rotation curves; stellar dynamics; strong lensing) NFW(-like) mass profile Isothermal(-like) profile (simulation) M σ

  15. Linking M to σ: • recent N-body simulation results + • the SDSS VDF and strong lensing • To study galaxy formation mechanisms involving baryonic physics • -To probe dark energy and galaxy formation together

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