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COSMIC MAGNIFICATION the other weak lensing signal

COSMOS 2010 Jes Ford. COSMIC MAGNIFICATION the other weak lensing signal. Jes Ford UBC graduate student In collaboration with: Ludovic Van Waerbeke. Jason Rhodes Alexis Finoguenov. Alexie Leauthaud Hendrik Hildebrandt. COSMOS 2010 Jes Ford. Motivation.

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COSMIC MAGNIFICATION the other weak lensing signal

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  1. COSMOS 2010 Jes Ford COSMIC MAGNIFICATIONthe other weak lensing signal Jes Ford UBC graduate student In collaboration with: Ludovic Van Waerbeke Jason Rhodes Alexis Finoguenov Alexie Leauthaud Hendrik Hildebrandt

  2. COSMOS 2010 Jes Ford Motivation • Dark Matter Halo measurements constrain cosmological parameters and structure formation • Weak Lensing has become an excellent cosmological probe of halos, but so far only to modest redshifts (zL < 1) • Future surveys attempt to optimize the lensing science, requiring good photo-z’s • Magnification can be measured too, without needing additional data

  3. COSMOS 2010 Jes Ford Magnification Basics • Galaxies behind a foreground matter overdensity are gravitationally lensed • 2 competing effects of magnification: • Flux Amplification: sources get brighter • Dilution: solid angle on the sky is stretched • Who wins? Depends on slope of source number counts at that magnitude…

  4. COSMOS 2010 Jes Ford Dilution & Amplification • Point: text • Point: text • Point: text Lensing conserves surface brightness

  5. COSMOS 2010 Jes Ford Shear & Magnification The vast majority of weak lensing studies measure shear (shapes) • Why Shear? • Signal-to-Noise:factor ~ 5 higher for shear (same sources) • Why Magnification? • Don’t need shapes, just magnitudes & photo-z’s • Can probe much higher redshifts where source galaxies are unresolved (S/N  factor ~ 2-3 higher for shear) • Why not both? • Completely different systematics • Can break degeneracies in M & 8 • Magnification comes along basically for free

  6. COSMOS 2010 Jes Ford Theory Dilution Amplification • Dilution vs Amplification: • WL limit: magnification  ≈ 1, and to first order depends only on convergence • Slope of number counts: • (-1) > 0 : amplification wins - we see more sources • (-1) < 0 : dilution wins - we see less sources • (-1) = 0 : effects cancel out - no change in source density

  7. COSMOS 2010 Jes Ford Steps to measuring  • Lenses: • Xray selected groups1 in the COSMOS field, chosen with z < 1, M > 3.98  1013 M • Additional Xray groups2 in CFHTLS D1, D4 • Sources: • LBG galaxies3 at z ≈ 3, from CFHTLS D1, D2, D4 • COSMOS30 galaxies, 1.2 < z < 6 • Redshift separation & masking crucial • Cross-correlate: stacked lenses and sources in different magnitude bins… expect positive, negative, or no correlation depending on (-1) • Combine magnitude bins: weighting by (-1) 1. A. Leauthaud 2. A. Finoguenov 3. H. Hildebrandt

  8. COSMOS 2010 Jes Ford Results: CFHTLS LBGs Number counts of LBGs used (-1) vs mag Hildebrandt et al. 2009

  9. COSMOS 2010 Jes Ford Results: CFHTLS LBGs Number counts of LBGs used (-1) vs mag Hildebrandt et al. 2009

  10. COSMOS 2010 Jes Ford Results: CFHTLS LBGs Number counts of LBGs used (-1) vs mag Hildebrandt et al. 2009 Bright LBGs are correlated Faint LBGs are anti-correlated

  11. COSMOS 2010 Jes Ford Results: CFHTLS LBGs Signal from combined magnitude bins Separate Mag Bins

  12. COSMOS 2010 Jes Ford Brightest Source Selection Results: COSMOS30(preliminary) Correlation strength nicely decreases with increasing magnitude selection ie, with decreasing slope (-1) Faintest Selection

  13. COSMOS 2010 Jes Ford Future Work • Optimal weighting: of (-1) on individual galaxies, not by average of magnitude bin • Ideal source redshift selection: chosen for each foreground lens separately • More sky coverage: will decrease uncertainties • Dust absorption: by lenses is only ~ few % effect, but can be probed simultaneously

  14. COSMOS 2010 Jes Ford Prospects for DM Halos • Prediction for 200 deg2 survey: • Lenses: 135 stacked halos at z = 1, V200= 950 km/s, c200= 4.5 • Sources: realistic number of LBGs, all at z = 3 • Promising method for weighing high-z dark matter halos Van Waerbeke et al. 2009

  15. Cosmos 2010 Jes Ford Conclusions • Magnification: • will provide independent cosmological constraints • different systematics  useful cross-check • is complementary to shear, does not replace it • Future Wide & Deep Surveys: • will require accurate photo-z’s for shear • magnification measurements possible without additional data • If we ONLY do shear analysis, we IGNORE many unresolved galaxies whose shapes can’t be measured • Lets make full use of our shear catalogs and exploit the magnification signal as well! Thanks for Listening!

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