Exploring the high-mass end of the stellar mass function of star-forming galaxies at cosmic noon

We present the high-mass end of the galaxy stellar mass function using the largest sample to date (5352) of star-forming galaxies with M_⋆ > 10¹¹ M_⊙ at cosmic noon, 1.5 < z < 3.5. This sample is uniformly selected across 17.2 deg² (∼0.44 Gpc³ comoving volume from 1.5 < z < 3.5), mitigating the effects of cosmic variance and encompassing a wide range of environments. This area, a factor of 10 larger than previous studies, provides robust statistics at the high-mass end. Using multiwavelength data in the Spitzer/HETDEX Exploratory Large Area (SHELA) footprint, we find that the SHELA footprint star-forming galaxy stellar mass function is steeply declining at the high-mass end probing values as high as ∼10^-4 Mpc³ dex^-1 and as low as ∼5 × 10^-8 Mpc³ dex^-1 across a stellar mass range of log(M_⋆/M_⊙) ∼ 11-12. We compare our empirical star-forming galaxy stellar mass function at the high-mass end to three types of numerical models: hydrodynamical models from IllustrisTNG, abundance matching from the UniverseMachine, and three different semi-analytical models (SAMs; SAG, SAGE, GALACTICUS). At redshifts 1.5 < z < 3.5, we find that results from IllustrisTNG and abundance matching models agree within a factor of ∼2-10, however the three SAMs strongly underestimate (up to a factor of 1000) the number density of massive galaxies. We discuss the implications of these results for our understanding of galaxy evolution.