It is now widely recognized that simulation-based models optimized to fit the clustering of massive galaxies overestimate their gravitational lensing on small scales, which is commonly known as the "lensing-is-low problem." One prevalent interpretation of this problem is that it is another manifestation of the tension between growth measurements from the early and late universe, known as the S8 tension.
However, in Chaves-Montero, Angulo, and Contreras (2023), we showed that this problem reflects shortcomings of galaxy-halo connection models rather than tensions within the ΛCDM paradigm itself. Specifically, it stems from neglecting various effects related to galaxy formation, such as assembly bias, the spatial segregation of satellite galaxies compared to dark matter, and the influence of baryonic effects on the mass distribution. All these effects contribute to overestimating gravitational lensing, and when combined, they explain the amplitude and scale dependence of the lensing-is-low problem. We thus concluded that simplistic galaxy-halo connection models are inadequate for the simultaneous interpretation of clustering and lensing.
Having identified the root cause of the problem, our focus shifted towards finding a solution. In Contreras, Angulo, Chaves-Montero et al. (2023), we studied the precision of SubHalo Abundance Matching extended model (SHAMe) -- a sophisticated galaxy-halo connection model -- jointly modeling clustering and lensing. Our study demonstrated that SHAMe successfully reproduces the projected clustering, correlation function multipoles, and excess surface density of galaxies from a state-of-the-art hydrodynamical simulation. Therefore, it does not suffer from the "artificial" lensing-is-low problem.
Encouraged by these results, in Contreras, Chaves-Montero, and Angulo (2023), we employed SHAMe to fit the clustering and lensing of massive galaxies from the BOSS survey. We found that SHAMe accurately reproduces the clustering and lensing of BOSS galaxies at all redshifts, confirming that this model does not suffer from the "artificial" lensing-is-low problem. On the other hand, we found that the additional flexibility of the model comes at the cost of losing constraining power. For example, we found that BOSS data is not constraining enough to discriminate between a Planck and low-S8 cosmology when analyzed using SHAMe.
Presently, we are working on modeling additional observables in SHAMe to break degeneracies between cosmological and model parameters.
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