1 / 26

Giant Arcs: A Probe for Clusters and Cosmogony

Giant Arcs: A Probe for Clusters and Cosmogony. Shude Mao. Jodrell Bank Observatory. Sept 28, 2006. COLLABORATORS: Guoliang Li , Yipeng Jing, Xi Kang, Weipeng Lin (SHAO) Matthias Bartelmann, Massimo Menegentti (Heidelberg) Liang Gao (Durham). A2218. Z=0.175.

amymckee
Download Presentation

Giant Arcs: A Probe for Clusters and Cosmogony

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. Giant Arcs: A Probe for Clusters and Cosmogony Shude Mao Jodrell Bank Observatory Sept 28, 2006 COLLABORATORS: Guoliang Li, Yipeng Jing, Xi Kang, Weipeng Lin (SHAO) Matthias Bartelmann, Massimo Menegentti (Heidelberg) Liang Gao (Durham)

  2. A2218 Z=0.175 Giant arcs are background galaxies distorted into long arcs by foreground clusters

  3. A1689 Z=0.18 Observations can determine, arc L/W ratio, width, source redshift & arc frequency

  4. Observational samples of giant arcs • Luppino et al. (1999) found strong lensing in eight out of 38 X-ray selected clusters • Optically, Zaritsky & Gozalez (2003) using LCRS and Gladders et al. (2003) using RCS found high fractions • Sand, Ellis, Treu, & Smith (2005) found 104 candidate tangential arcs in 128 clusters with HST • Giant arcs appear common in massive clusters

  5. Why do we study giant arcs? • Giant arcs probe the largest bound structures in the universe • Their numbers and positions are a sensitive probe of cluster properties including their abundance and mass profiles • Their numbers are also sensitive to the cosmogony, particularly the power-spectrum normalisation σ8 • Clusters are nature telescope, allowing us to study faint, high-redshift background objects behind clusters

  6. How do we model giant arcs? • Earlier studies used analytical spherical models (e.g. Wu & Hammer 1993; Wu & Mao 1996). • But clusters are complex (ellipticities, substructures, mergers). • Most recent studies use numerically simulated clusters • Bartelmann and associates (1998-) • Dalal et al. (2004) • Wambsganss, Ostriker, Bode (2004): 3D ray-tracing • Li, Mao, Jing, Bartelmann, Kang, Meneghetti (2005)

  7. Numerical simulation • N-body simulation was performed by Jing (2000) in CDM cosmology (m=0.3, 8=0.9) • Dark matter only, 5123 particles • Box size: 300/h Mpc, 30/h kpc (comoving) resolution • 200 massive clusters are selected using the friends-of-friends algorithm, from redshift 0.1, 0.2, …, 2.5 • Background source population • At redshift 0.6, 1.0, 1.4, …., 7 • Sources have 0.5, 1, 1.5 arcsecond effective diameters • Ellipticity (=1-b/a), uniformly distributed from 0.5 to 1 • Calculate the cross-section for each cluster, and then integrate to obtain the total lensing optical depth.

  8. A high-resolution numerical cluster Clusters are complex (e.g. tri-axial with significant substructures) Jing (2000)

  9. From particles to smooth density fields • Simulations give discreet particle positions • Need an efficient and high-fidelity smoothing algorithm from position to density field • We proposed an adaptive smoothing algorithm based on the scatter interpretation of SPH (Li et al. 2006) • First partitions particle weights in 3D grids according to SPH (for Nneighbor=32, 64). • Then integrate along the line of sight to obtain surface density • Fully adaptive, and better preserves substructures than other methods

  10. Caustics and critical curves z=0.3, M~1015/h Msun

  11. Optical depth as a function of source redshift • Optical depth ~ 10-7 for deff=0.5”, for zs=1; but 10-6 for zs=3 • Lower than several previous studies • Agree with Dalal et al. (2004), who claimed consistency with observations in the CDM cosmology. • Strong zs dependence • Weaker dependence on ellipticity and source size

  12. Optical depth as a function of cluster mass • Cutoffs at both low-mass and high-mass tails • Need to sample the mass function sufficiently

  13. Optical depth as a function of lens redshift • For sources at high z, probe clusters at high redshift • Hoekstra et al. who found all three of their lensing clusters were at z>0.62; understood if source z is high.

  14. Width of giant arcs • ~ r-β, width/diameter ~ 1/(β-1) • If β =2 (isothermal sphere), width/diameter=1 • Width can be used as a probe of the cluster potential and the background source population

  15. Observed size distribution from HST Ferguson et al. (2004) Half-light radius Appears to be consistent with HST CDF/HDF observations of high-z galaxies

  16. Giant arcs in the WMAP three year cosmology • The WMAP three-year model has lower m and 8 compared with the usual LCDM model. • The lower m (0.238) and 8 (0.74) both reduce the number of giants • We compared arc predictions in the usual CDM and WMAP three-year models: • Using two 300/h Mpc N-body simulations • The predicted number is reduced by a factor of about six in the WMAP three year model

  17. Predicted number of giant arcs Z=0.3 A factor of 6 • Effects of source size and ellipticity are modest • Effect of star formation? Maybe a factor of 2 (Meneghetti et al. 2003). Overcooling. • Largest uncertainty: source redshift distribution

  18. Summary • Optical depth may be too low in the WMAP three-year model (with 8=0.74) • But the source redshift distribution and effects of star formation are still uncertain • Properties of giant arcs (e.g., widths) can be used to probe of the intrinsic size of high-redshift sources and the cluster potential. • We need many larger giant arc samples, which will come as by-products of weak lensing surveys. • A combination of strong and weak lensing can probe clusters more robustly.

  19. Future works • What is the effect of baryons? • More realistic comparisons with observations • In particular, giant arcs in x-ray selected clusters • Are lensed clusters typical? Tests of the NFW profile. • Explore how the width of giant arcs can be used to probe properties of clusters and high-redshift source population • Constrain the power-spectrum normalisation and cosmogony

  20. Effects of source ellipticity • Effect of ellipticity is around 30-50%

  21. Effects of source size • Source size change results by a factor of ~1.5-2

  22. Comparison with previous studies • Two previous studies claim their predictions are consistent with observations • Our optical depth is lower than Bartelmann et al. (1998) by a factor of 10 because their σ8 (1.12) is too high • Sensitive to cosmogony & dark energy

  23. Comparison with previous studies • Wambsganss, Ostriker & Bode (2004) • Too high by a factor of ten • Assumption L/W=μ is incorrect • More or less consistent with Dalal et al. (2004), but their simulation volume may be too small (box size: 100/h Mpc)!

  24. Dark matter (energy) discussions • Do we really need it? MOND? • Evidence for dark matter in galaxies & clusters • Disc galaxies (rotation curve, satellite galaxies) • Elliptical galaxies (dynamics, lensing, x-ray) • Clusters (x-ray, lensing) • Large-scale structure, CMB • Substructures: • too many predicted? • Implications of new satellites found by SDSS in the MW. • Density profiles of dark matter haloes? • Density slopes? Too concentrated (from rotation curve, Tully-Fisher relation)? • Distribution of dark matter in galaxies as a function of radius • Maximal or minimal disks? • Fast bar pattern speed? • Galactic microlesning • What is it? • Cold, hot or warm? Collisionless or self-interacting? • Experimental status of direct search

  25. New satellites in the MW Belokurov et al. 2006

  26. CDM direct search

More Related