Clustering and Halo Abundances in Early Dark Energy Cosmological Models

Abstract: LCDM cosmological models with Early Dark Energy (EDE) have been proposed to resolve tensions between the Hubble constant H0 = 100h km/s/Mpc measured locally, giving h ~ 0.73, and H0 deduced from Planck cosmic microwave background (CMB) and other early universe measurements plus LCDM, giving h ~ 0.67. EDE models do this by adding a scalar field that temporarily adds dark energy equal to about 10% of the cosmological energy density at the end of the radiation-dominated era at redshift z ~ 3500. Here we compare linear and nonlinear predictions of a Planck-normalized LCDM model including EDE giving h = 0.728 with those of standard Planck-normalized LCDM with h = 0.678. We find that nonlinear evolution reduces the differences between power spectra of fluctuations at low redshifts. As a result, at z = 0 the halo mass functions on galactic scales are nearly the same, with differences only 1-2%. However, the differences dramatically increase at high redshifts. The EDE model predicts 50% more massive clusters at z = 1 and twice more galaxy-mass halos at z = 4. Even greater increases in abundances of galaxy-mass halos at higher redshifts may make it easier to reionize the universe with EDE. Predicted galaxy abundances and clustering will soon be tested by JWST observations. Positions of baryonic acoustic oscillations (BAOs) and correlation functions differ by about 2% between the models -- an effect that is not washed out by nonlinearities. Both standard LCDM and the EDE model studied here agree well with presently available acoustic-scale observations, but DESI and Euclid measurements will provide stringent new tests.