Impact of Weak Lensing Mass Calibration on eROSITA Galaxy Cluster Cosmological Studies -- a Forecast

TL;DR

This paper forecasts how weak lensing mass calibration can improve cosmological constraints from eROSITA galaxy cluster counts, highlighting potential precision gains and limitations due to parameter degeneracies.

Contribution

It introduces a comprehensive forecast analysis of the impact of weak lensing calibration on eROSITA cluster cosmology, incorporating mock catalogs and various survey scenarios.

Findings

Forecasted parameter uncertainties for key cosmological parameters.

Degeneracy between distance-redshift relation and observable-mass scaling.

Potential improvements with BAO measurements and systematics control.

Abstract

We forecast the impact of weak lensing (WL) cluster mass calibration on the cosmological constraints from the X-ray selected galaxy cluster counts in the upcoming eROSITA survey. We employ a prototype cosmology pipeline to analyze mock cluster catalogs. Each cluster is sampled from the mass function in a fiducial cosmology and given an eROSITA count rate and redshift, where count rates are modeled using the eROSITA effective area, a typical exposure time, Poisson noise and the scatter and form of the observed X-ray luminosity-- and temperature--mass--redshift relations. A subset of clusters have mock shear profiles to mimic either those from DES and HSC or from the future Euclid and LSST surveys. Using a count rate selection, we generate a baseline cluster cosmology catalog that contains 13k clusters over 14,892~deg$^2$ of extragalactic sky. Low mass groups are excluded using raised count rate thresholds at low redshift. Forecast parameter uncertainties for $\Omega_\mathrm{M}$, $\sigma_8$ and $w$ are 0.023 (0.016; 0.014), 0.017 (0.012; 0.010), and 0.085 (0.074; 0.071), respectively, when adopting DES+HSC WL (Euclid; LSST), while marginalizing over the sum of the neutrino masses. A degeneracy between the distance--redshift relation and the parameters of the observable--mass scaling relation limits the impact of the WL calibration on the $w$ constraints, but with BAO measurements from DESI an improved determination of $w$ to 0.043 becomes possible. With Planck CMB priors, $\Omega_\text{M}$ ($\sigma_8$) can be determined to $0.005$ ($0.007$), and the summed neutrino mass limited to $\sum m_\nu < 0.241$ eV (at 95\%). If systematics on the group mass scale can be controlled, the eROSITA group and cluster sample with 43k objects and LSST WL could constrain $\Omega_\mathrm{M}$ and $\sigma_8$ to 0.007 and $w$ to 0.050.