The Supersonic Project: Lighting Up the Faint End of the JWST UV Luminosity Function

Abstract

The James Webb Space Telescope (JWST) is capable of probing extremely early eras of our Universe, when the supersonic relative motions between dark matter and baryonic overdensities modulate structure formation (z ≳ 10). We study low-mass galaxy formation, including this “stream velocity,” using high-resolution AREPO hydrodynamics simulations and present theoretical predictions of the UV luminosity function (UVLF) and galaxy stellar mass function down to extremely faint and low-mass galaxies (M UV ≳ −15, 104 M ⊙ ≤ M * ≤ 108 M ⊙). We show that, although the stream velocity suppresses early star formation overall, it induces a short period of rapid star formation in some larger dwarfs, leading to an enhancement in the faint end of the UVLF at z = 12. We demonstrate that JWST observations are close to this enhanced regime and propose that the UVLF may constitute an important probe of the stream velocity at high redshift for JWST and future observatories.