What can we learn from Gravitational Magnification

with BigBOSS?

Alexie LeauthaudLBNL & BCCP

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Kung Fu?

Alexie Leauthaud BigBOSS meeting 2009

Gravitational MagnificationGravitational Magnification

Image credit: Joerg Colberg, Ryan Scranton, Robert Lupton, SDSS

Foreground PopulationCross-correlation between Background Population &

Alexie Leauthaud BigBOSS meeting 2009

Science with magnification?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.

Alexie Leauthaud BigBOSS meeting 2009

Gravitational MagnificationGravitational 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.

Alexie Leauthaud BigBOSS meeting 2009

Systematics effectsSystematics 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)

Alexie Leauthaud BigBOSS meeting 2009

Magnification in SDSSMagnification in SDSS

Scranton et al. 2005

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Alexie Leauthaud BigBOSS meeting 2009

Dependence on the slope of the number countsDependence on the slope of the number counts

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Scranton et al. 2005

>1

=1

<1

Alexie Leauthaud BigBOSS meeting 2009

Dependence on the slope of the number countsDependence on the slope of the number counts

magnitude

log

( n

umbe

r_d

ensi

ty(m

ag)

)

mag

lim

it

>1=1

Dilation of sky solid angle

Magnification

Positive galaxy-QSO cross-correlation

Alexie Leauthaud BigBOSS meeting 2009

Dependence on the slope of the number countsDependence on the slope of the number counts

magnitude

mag

lim

it

<1

=1

Dilation of sky solid angle

Magnification

Negative galaxy-QSO cross-correlation

log

( n

umbe

r_d

ensi

ty(m

ag)

)

Alexie Leauthaud BigBOSS meeting 2009

Magnification in CFHTLS DeepMagnification in CFHTLS Deep

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Hildebrant et al. 2005

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Alexie Leauthaud BigBOSS meeting 2009

The numbersThe 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, 2.8x107

Emission Line Galaxies, 1.5<z<2.0, 1.3x107

LRGs, z<0.7, 7x106

QSO, 1<z<2,1.5x106

~ 5x107 background objects

Alexie Leauthaud BigBOSS meeting 2009

Foreground

Photoz

Foreground

Specz

Background

Photoz

Background

Specz

Scranton 2005

1.3x107 x 200,000 x

Menard

20092x107 x 85,000 x

Hildebrandt

2009unclear x 80,000 x

BOSS ? 1.5x106 ? 160,000

Big BOSS ? 7x106 6.8x107 4.4x107

8

4-8

?

Alexie Leauthaud BigBOSS meeting 2009

From SDSS to BOSSFrom 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

≈

≈

Alexie Leauthaud BigBOSS meeting 2009

From BOSS to BigBOSSFrom 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

≈

Alexie Leauthaud BigBOSS meeting 2009

Shear versus magnificationShear versus magnification

SHEARSHEAR

• Shear calibration

• PSF correction

• Intrinsic alignment

• Statistics (see van Waerbeke 2009)

• Scales with m2

MAGNIFICATIONMAGNIFICATION

• 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

Alexie Leauthaud BigBOSS meeting 2009

Yet to be investigated ….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 ….

Thank you

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

BigBOSS