## This content will become publicly available on November 5, 2020

# Disentangling magnification in combined shear-clustering analyses

## Abstract

ABSTRACT We investigate the sensitivity to the effects of lensing magnification on large-scale structure analyses combining photometric cosmic shear and galaxy clustering data (i.e. the now commonly called ‘3 × 2-point’ analysis). Using a Fisher matrix bias formalism, we disentangle the contribution to the bias on cosmological parameters caused by ignoring the effects of magnification in a theory fit from individual elements in the data vector, for Stage-III and Stage-IV surveys. We show that the removal of elements of the data vectors that are dominated by magnification does not guarantee a reduction in the cosmological bias due to the magnification signal, but can instead increase the sensitivity to magnification. We find that the most sensitive elements of the data vector come from the shear-clustering cross-correlations, particularly between the highest redshift shear bin and any lower redshift lens sample, and that the parameters ΩM, $$S_8=\sigma _8\sqrt{\Omega _\mathrm{ M}/0.3}$$, and w0 show the most significant biases for both survey models. Our forecasts predict that current analyses are not significantly biased by magnification, but this bias will become highly significant with the continued increase of statistical power in the near future. We therefore conclude that future surveys should measure and model the magnification as part of their flagship ‘3 × 2-point’ analysis.

- Authors:

- Astrophysics, Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK, Perimeter Institute, 31 Caroline Street North, Waterloo, ON N2L 2Y5, Canada, Department of Physics and Astronomy, University of Waterloo, Waterloo, ON N2L 3G1, Canada
- Astrophysics, Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK

- Publication Date:

- Sponsoring Org.:
- USDOE

- OSTI Identifier:
- 1576662

- Resource Type:
- Published Article

- Journal Name:
- Monthly Notices of the Royal Astronomical Society

- Additional Journal Information:
- Journal Name: Monthly Notices of the Royal Astronomical Society Journal Volume: 491 Journal Issue: 2; Journal ID: ISSN 0035-8711

- Publisher:
- Oxford University Press

- Country of Publication:
- United Kingdom

- Language:
- English

### Citation Formats

```
Thiele, Leander, Duncan, Christopher A. J., and Alonso, David. Disentangling magnification in combined shear-clustering analyses. United Kingdom: N. p., 2019.
Web. doi:10.1093/mnras/stz3103.
```

```
Thiele, Leander, Duncan, Christopher A. J., & Alonso, David. Disentangling magnification in combined shear-clustering analyses. United Kingdom. doi:10.1093/mnras/stz3103.
```

```
Thiele, Leander, Duncan, Christopher A. J., and Alonso, David. Tue .
"Disentangling magnification in combined shear-clustering analyses". United Kingdom. doi:10.1093/mnras/stz3103.
```

```
@article{osti_1576662,
```

title = {Disentangling magnification in combined shear-clustering analyses},

author = {Thiele, Leander and Duncan, Christopher A. J. and Alonso, David},

abstractNote = {ABSTRACT We investigate the sensitivity to the effects of lensing magnification on large-scale structure analyses combining photometric cosmic shear and galaxy clustering data (i.e. the now commonly called ‘3 × 2-point’ analysis). Using a Fisher matrix bias formalism, we disentangle the contribution to the bias on cosmological parameters caused by ignoring the effects of magnification in a theory fit from individual elements in the data vector, for Stage-III and Stage-IV surveys. We show that the removal of elements of the data vectors that are dominated by magnification does not guarantee a reduction in the cosmological bias due to the magnification signal, but can instead increase the sensitivity to magnification. We find that the most sensitive elements of the data vector come from the shear-clustering cross-correlations, particularly between the highest redshift shear bin and any lower redshift lens sample, and that the parameters ΩM, $S_8=\sigma _8\sqrt{\Omega _\mathrm{ M}/0.3}$, and w0 show the most significant biases for both survey models. Our forecasts predict that current analyses are not significantly biased by magnification, but this bias will become highly significant with the continued increase of statistical power in the near future. We therefore conclude that future surveys should measure and model the magnification as part of their flagship ‘3 × 2-point’ analysis.},

doi = {10.1093/mnras/stz3103},

journal = {Monthly Notices of the Royal Astronomical Society},

number = 2,

volume = 491,

place = {United Kingdom},

year = {2019},

month = {11}

}

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