Massive Dark Matter Halos at High Redshift: Implications for Observations in the JWST Era

Abstract

The presence of massive galaxies at high $z$ as recently observed by JWST appears to contradict the current $\Lambda$CDM cosmology. Here we aim to alleviate this tension by incorporating uncertainties from three sources in counting galaxies: cosmic variance, error in stellar mass estimation, and backsplash enhancement. Each of these factors significantly increases the cumulative stellar mass density $\rho_*(>M_*)$ at the high-mass end, and their combined effect can boost the density by more than one order of magnitude. Assuming a star formation efficiency of $\epsilon_* \sim 0.5$, cosmic variance alone reduces the tension to a $2\sigma$ level, except for the most massive galaxy at $z=8$. Additionally, incorporating a 0.3 dex lognormal dispersion in the stellar mass estimation brings the observed $\rho_*(>M_*)$ at $z \sim 7 - 10$ within $2\sigma$. The tension is completely eliminated when we account for the gas stripped from backsplash halos. These results highlight the importance of fully modeling uncertainties when interpreting observational data of rare objects. We use the constrained simulation, ELUCID, to investigate the descendants of high-$z$ massive galaxies. Our findings reveal that a significant portion of these galaxies ultimately reside in massive halos at $z=0$ with $M_{\rm halo} > 10^{13} h^{-1}M_\odot$. Moreover, a large fraction of local central galaxies in $M_{\rm halo} \geqslant 10^{14.5} h^{-1}M_\odot$ halos are predicted to contain substantial amounts of ancient stars formed in massive galaxies at $z \sim 8$. This prediction can be tested by studying the structure and stellar population of central galaxies in present-day massive clusters.