Cross-correlation of spectroscopic and photometric galaxy surveys: cosmology from lensing and redshift distortions

Abstract

Cosmological galaxy surveys aim at mapping the largest volumes to test models\nwith techniques such as cluster abundance, cosmic shear correlations or baryon\nacoustic oscillations (BAO), which are designed to be independent of galaxy\nbias. Here we explore an alternative route to constrain cosmology: sampling\nmore moderate volumes with the cross-correlation of photometric and\nspectroscopic surveys. We consider the angular galaxy-galaxy autocorrelation in\nnarrow redshift bins and its combination with different probes of weak\ngravitational lensing (WL) and redshift space distortions (RSD). Including the\ncross-correlation of these surveys improves by factors of a few the constraints\non both the dark energy equation of state w(z) and the cosmic growth history,\nparametrized by \\gamma. The additional information comes from using many narrow\nredshift bins and from galaxy bias, which is measured both with WL probes and\nRSD, breaking degeneracies that are present when using each method separately.\nWe show forecasts for a joint w(z) and \\gamma figure of merit using linear\nscales over a deep (i<24) photometric survey and a brighter (i<22.5)\nspectroscopic or very accurate (0.3%) photometric redshift survey.\nMagnification or shear in the photometric sample produce FoM that are of the\nsame order of magnitude of those of RSD or BAO over the spectroscopic sample.\nHowever, the cross-correlation of these probes over the same area yields a FoM\nthat is up to a factor 100 times larger. Magnification alone, without shape\nmeasurements, can also be used for these cross-correlations and can produce\nbetter results than using shear alone. For a spectroscopic follow-up survey\nstrategy, measuring the spectra of the foreground lenses to perform this\ncross-correlation provides 5 times better FoM than targeting the higher\nredshift tail of the galaxy distribution to study BAO over a 2.5 times larger\nvolume.\n