Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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 • 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. • Consider the following parameterization for the evolution of the DE equation of state p (EOS) w: x x z w( z ) w0 w1 z 1 (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 Key cosmological factor: H 0 dt 1 dz (1 z ) E ( z ) H ( z) E( z) m 0 (1 z ) 3 x 0 X ( z ) k 0 (1 z ) 2 H0 ( m 0 x 0 k 0 1) x ( z) z 3[1 w( z )] X ( z) exp dz x0 0 1 z Cosmological distances [dL(z), dA(z)] depend on this factor. 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. ], d L (z) WMAP 3-year results: angular-diameter distance of the sound horizon at zdec [inv. ] d A (z) SDSS luminous red galaxies: baryonic acoustic-peak oscillations (BAO) [inv. ] ….. d A (z) Nesseris & Perivolaropoulos (2007) Wu & Yu (2007) • 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. 3. Lens Statistics Test of DE Multiple-imaging (strong lensing) probability: H 0 dt RH n( z ) s Bdz dz dn d d n(z): number density, e.g. s: cross section. B: magnification bias Differential probability: d dz d 2 dzd dn dM dM • 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. Ωm0=0.2 Ωm0=0.25 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). 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 (Theory) (observation) (simulation) dn dM dn d (simulation) NFW(-like) mass profile Isothermal(like) profile M σ (spectroscopic survey; strong lensing) (rotation curves; stellar dynamics; strong lensing) Linking M to σ: recent N-body simulation results + the SDSS VDF and strong lensing -To study galaxy formation mechanisms baryonic physics involving -To probe dark energy and galaxy formation together