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

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

2. Kung Fu?

3. Cross-correlation between Background Population & Foreground Population Gravitational Magnification Image credit: Joerg Colberg, Ryan Scranton, Robert Lupton, SDSS

4. 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. 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. 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. Magnification in SDSS Scranton et al. 2005

8. <1 =1 >1 Dependence on the slope of the number counts Scranton et al. 2005

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

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

11. Magnification in CFHTLS Deep Hildebrant et al. 2005

12. The numbers • Scranton et al. 20051.3x107 galaxies, 200,000 QSOs • Menard et al. 20092.107 galaxies at <z>=0.36, 17<i<2, 85,000 QSOs, Photometry in 5 different bands to measure dust extinction • Hildebrandt et al. 2009foreground? , 80,000 LBGs at 2.5<z<5 from CFHTLS Deep • BOSS 1.5x106 LRGs at z<0.7, 160,000 QSOs at 2.2<z<3 • BigBOSSEmission Line Galaxies, 0.7<z<1.5, 2.8x107Emission Line Galaxies, 1.5<z<2.0, 1.3x107LRGs, z<0.7, 7x106QSO, 1<z<2,1.5x106 ~ 5x107 background objects

13. ?  8 4-8

14. 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. 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. Shear versus magnification • 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 • SHEAR • Shear calibration • PSF correction • Intrinsic alignment • Statistics (see van Waerbeke 2009) • Scales with m2

17. Magnification is like galaxy-galaxy lensing about 5 years ago …. 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.

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