The Most Massive Galaxies and Black Holes Allowed by $\Lambda$CDM

Understand

Given a galaxy's stellar mass, its host halo mass has a lower limit from the cosmic baryon fraction and known baryonic physics.

• At z>4, galaxy stellar mass functions place lower limits on halo number densities that approach expected $\Lambda$CDM halo mass functions.
• High-redshift galaxy stellar mass functions can thus place interesting limits on number densities of massive haloes, which are otherwise very difficult to measure.
• Although halo mass functions at z<8 are consistent with observed galaxy stellar masses if galaxy baryonic conversion efficiencies increase with redshift, JWST and WFIRST will more than double the redshift range over which useful constraints are available.