From photometric surveys to HI intensity mapping: Improving constraints on magnification biases while testing gravity

Abstract

The observed large-scale structure of the Universe is not a direct measure on the underlying distribution of matter. These observations are subtly distorted by gravitational lensing effects, which leave imprints on the statistical distribution of galaxies and offer powerful test of general relativity. In this work, we investigate whether HI intensity mapping from current and forthcoming surveys can improve constraints on magnification lensing obtained from photometric galaxy surveys. In particular, can we jointly constrain the magnification bias parameters $s^\mathrm{G}(z)$ and the amplitude of the Weyl potential, which we parametrise as $β$. We employ a Fisher matrix formalism in order to estimate future constrains on the magnification biases and $β$. We forecast constraints for three photometric surveys (DES-like, LSST-like, Euclid-like) individually and with two HI intensity mapping surveys (MeerKLASS, SKAO). We apply the multi-tracer technique by combining each galaxy survey with each HI survey, exploiting the combined constraining in the overlapping sky area. The multi-tracer approach dramatically improves constraints on $β$ by factors of 25 to 50, depending on the surveys considered. For $s^\mathrm{G}(z)$, improvements can be marginal or by a factors of 2 to 8. We also verify that $β$ and $s^\mathrm{G}(z)$ can be constrained simultaneously as the cross-correlations between tracers break the degeneracies among them. We conclude that the multi-tracer combination of photometric galaxy surveys and HI intensity mapping surveys enables high-precision measurements of both $s^\mathrm{G}(z)$ and $β$. This opens an additional pathway to constrain $Φ+Ψ$ and test the validity of general relativity on cosmological scales.

Figures (9)

• Figure 1: Values used for the number density of galaxies, $n_\mathrm{gal}$, the galaxy bias, $b^G(z)$, and the magnification bias, $s^G(z)$ of the three galaxy surveys considered. Markers indicate measured or tabulated values; lines represent fitted or interpolated functions used in our analysis.
• Figure 2: Redshift bins considered for the DES-like, LSST-like and Euclid-like surveys. The values of the central redshifts of each bin are shown in \ref{['tab:z_c_values']}.
• Figure 3: Redshift bins considered for the Hi Surveys MeerKLASS and SKAO.The values of the central redshifts of each bin are shown in \ref{['tab:z_c_values']}
• Figure 4: Values of the system temperatures, $T_\mathrm{sys}$, used in the analysis that includes Hi IM surveys.
• Figure 5: Corner plot showing the uncertainties of each cosmological parameter when constrained with data from the DES-like and MeerKLASS Surveys.