Euclid preparation: XIX. Impact of magnification on photometric galaxy clustering

We investigate the importance of lensing magnification for estimates of galaxy clustering and its cross-correlation with shear for the photometric sample of Euclid. We find that magnification significantly affects both the best-fit estimation of cosmological parameters and the constraints in the galaxy clustering analysis of the photometric sample. In particular, including magnification in the analysis reduces the 1σ errors on Ωm,0,w0,wa at the level of 20-35%, depending on how well we will be able to independently measure the local count slope. In addition, we find that neglecting magnification in the clustering analysis leads to shifts of up to 1.6σ in the best-fit parameters. In the joint analysis of galaxy clustering, cosmic shear and galaxy-galaxy lensing, including magnification does not improve precision but it leads to up to 6σ bias if neglected. For all models considered in this work, magnification has to be included in the analysis of galaxy clustering and its cross-correlation with the shear signal (3×2pt analysis) for accurate parameter estimation.