The SRG/eROSITA All-Sky Survey. Early dark energy and Hubble constant from the cluster mass function

This is the authors' abstract. We don't add key points for this paper.

The evolution of the mass function of massive galaxy clusters is a well-established cosmological probe. Using the eROSITA X-ray instrument on board the (SRG) mission, the western Galactic hemisphere of eROSITA's first All-Sky Survey (eRASS1) delivers a uniformly selected and securely confirmed sample of 5259 galaxy clusters spanning 0.1 < z < 0.8. When combined with overlapping weak lensing data from DES Year 3, KiDS, and HSC for mass calibration, this dataset enables precise tests of the standard Λ cold dark matter (łcdm) framework and beyond. In this work, we used the 0.1 < z < 0.45 subsample of the eRASS1 galaxy cluster catalog to place constraints on an axion-like early dark energy (EDE) scenario. Such models have been proposed as a possible mechanism to alleviate the tension between early- and late-Universe measurements of the Hubble constant. In this framework, a scalar field temporarily enhances the cosmic expansion rate around the epoch of recombination, after which its energy density rapidly dilutes at later times, leaving distinct imprints on the growth of structure. We leveraged these signatures across a redshift and scale range that have rarely been covered in the literature to present the first constraints on EDE derived from galaxy cluster number counts. Using eRASS1 number counts alone, we obtained an upper limit on the maximum EDE fraction of f_ < 0.3, consistent with results from primary cosmic microwave background (CMB) analyses. This demonstrates that the cluster mass function provides a powerful and complementary probe of the EDE parameter space. Combining our cluster analysis with primary CMB measurements, baryon acoustic oscillations, and CMB lensing, while notably excluding distance-ladder calibration data, yields results that are consistent with a nonzero EDE contribution and H_ , ^ Spectrum Roentgen Gamma EDE values compatible with late-Universe measurements. The most significant detection, at sim3.2σ, arises from the joint analysis of the eRASS1 cluster sample with the full set of external datasets. This yields f_ = , ^ EDE while placing competitive constraints on the critical redshift parameter, łogzc = łogzceRASSPACTLB, and leading to an inferred value of the Hubble constant: H_ =̋ZeroeRASSPACTLB ; ̊m km ̊m s -1 ̊m Mpc -1 .