1. What can we learn from Gravitational Magnification with BigBOSS? Alexie Leauthaud LBNL & BCCP

2. Kung Fu?

3. BigBOSS meeting 2009Alexie Leauthaud Gravitational Magnification Image credit: Joerg Colberg, Ryan Scranton, Robert Lupton, SDSS Foreground PopulationCross-correlation between Background Population &

4. BigBOSS meeting 2009Alexie Leauthaud Science with magnification?  David Schlegel this morning: multiple tracers of the mass distribution. Lensing tells us about the expansion history and the growth.  Measure the galaxy-mass cross-correlation function (halo properties, mass & concentration, bias). Sensitive to  instead of .  Combine magnification & clustering to constrain  m and  8 (Seljak et al. 2005, Yoo et al. 2006, Cacciato et al. 2009).  Constrain dust properties via wavelength dependant extinction (Menard et al. 2009).  Cosmic magnification? In the literature, this actually refers to the measurement of the galaxy-mass cross-correlation function (van Waerbeke 2009), so this is the equivalent of ‘galaxy-galaxy lensing’  Cosmic magnification tomography?  Magnification compared to shear: different systematics.

5. BigBOSS meeting 2009Alexie Leauthaud Gravitational Magnification (incomplete list) Seldner & Peebles 1979, Fugmann 1990, Bartelmann & Schneider 1993, Bartsch et al. 1997, Cooray 1999, Rodrigues-Williams & Hogan 1994, Seitz 7 Schneider 1995, Wu & Han 1995, Norman & Impey 1999, Croom & Shanks 1999, Myers et al. 2003, Gaztanga 2003, Scranton et al. 2005, Menard et al. 2009, Hildebrant et al. 2009. Historically controversial subject: results range from significant positive correlations to null and negative correlations and have disagreed with theoretical predictions. Many early results were probably contaminated by systematic errors. Cosmological magnification has been robustly detection since 2005 in a few studies only.

6. BigBOSS meeting 2009Alexie Leauthaud Systematics effects  Accuracy of the photometry  Redshift accuracy of the background sources (physical cross-correlations between close pairs will swamp the signal if the sources are not cleanly separated from the lenses)  Redshift accuracy of foreground sources (study signal as a function of physical transverse distance, r, rather than an angular separation,  )  QSO/star separation (stars will lead to a dilation of the signal)

7. BigBOSS meeting 2009Alexie Leauthaud Magnification in SDSS Scranton et al. 2005

8. BigBOSS meeting 2009Alexie Leauthaud Dependence on the slope of the number counts Scranton et al. 2005  >1  =1  <1

9. BigBOSS meeting 2009Alexie Leauthaud Dependence on the slope of the number counts magnitude log( number_density(mag) ) mag limit  >1  =1 Dilation of sky solid angle Magnification  Positive galaxy- QSO cross-correlation

10. BigBOSS meeting 2009Alexie Leauthaud Dependence on the slope of the number counts magnitude mag limit  <1  =1 Dilation of sky solid angle Magnification  Negative galaxy- QSO cross-correlation log( number_density(mag) )

11. BigBOSS meeting 2009Alexie Leauthaud Magnification in CFHTLS Deep Hildebrant et al. 2005

12. BigBOSS meeting 2009Alexie Leauthaud The numbers  Scranton et al. 2005 1.3x10 7 galaxies, 200,000 QSOs  Menard et al. 2009 2.10 7 galaxies at =0.36, 17<i<2, 85,000 QSOs, Photometry in 5 different bands to measure dust extinction  Hildebrandt et al. 2009 foreground?, 80,000 LBGs at 2.5<z<5 from CFHTLS Deep  BOSS 1.5x10 6 LRGs at z<0.7, 160,000 QSOs at 2.2<z<3  BigBOSS Emission Line Galaxies, 0.7<z<1.5, 2.8x10 7 Emission Line Galaxies, 1.5<z<2.0, 1.3x10 7 LRGs, z<0.7, 7x10 6 QSO, 1<z<2,1.5x10 6 ~ 5x10 7 background objects

13. BigBOSS meeting 2009Alexie Leauthaud Foreground Photoz Foreground Specz Background Photoz Background Specz Scranton 2005 1.3x10 7 x 200,000 x Menard 2009 2x10 7 x 85,000 x Hildebrandt 2009 unclear x 80,000 x BOSS? 1.5x10 6 ? 160,000 Big BOSS? 7x10 6 6.8 x10 7 4.4x10 7 88 4-8  ? 

14. BigBOSS meeting 2009Alexie Leauthaud From SDSS to BOSS  Accuracy of the photometry  Redshift accuracy of the background sources (physical cross-correlations will swamp the signal if the sources are not cleanly separated from the lenses)  Redshift accuracy of foreground sources  QSO/star separation (stars will lead to a dilation of the signal)  Statistics ≈ ≈

15. BigBOSS meeting 2009Alexie Leauthaud From BOSS to BigBOSS  Accuracy of the photometry  Redshift accuracy of the background sources (physical cross-correlations will swamp the signal if the sources are not cleanly separated from the lenses)  Redshift accuracy of foreground sources  QSO/star separation (stars will lead to a dilation of the signal)  Statistics ≈

16. BigBOSS meeting 2009Alexie Leauthaud Shear versus magnification SHEAR Shear calibration PSF correction Intrinsic alignment Statistics (see van Waerbeke 2009) Scales with  m 2 MAGNIFICATION Can be used for small galaxies Magnitudes are not difficult to measure Precise calibration of the number counts is required Dust extinction Scales with  m

17. BigBOSS meeting 2009Alexie Leauthaud Yet to be investigated …. Use sophisticated HOD analysis to model the magnification signal. Optimal weighting of the signal (for example, incorporate a weighting with ∑ crit ). Calculate the signal as a function of physical transverse distance as opposed to an angular scales. Calculate the signal around various galaxy types. Magnification is like galaxy-galaxy lensing about 5 years ago ….

18. Thank you If you are interested in thinking about magnification with BigBoss, please let me know! BigBOSS