The Size–Mass Relation at Rest-frame 1.5 μm from JWST/NIRCam in the COSMOS-WEB and PRIMER-COSMOS Fields

Abstract

We present the galaxy stellar mass–size relation in the rest-frame near-IR (1.5 μ m) and its evolution with redshift up to z = 2.5. Sérsic profiles are measured for ∼26,000 galaxies with stellar masses M _⋆ > 10 ^9 M _⊙ from JWST/NIRCam F277W and F444W imaging provided by the COSMOS-WEB and PRIMER surveys using coordinates, redshifts, colors, and stellar mass estimates from the COSMOS2020 catalog. The new rest-frame near-IR effective radii are generally smaller than previously measured rest-frame optical sizes, on average by 0.14 dex, with no significant dependence on redshift. For quiescent galaxies, this size offset does not depend on stellar mass, but for star-forming galaxies, the offset increases from −0.1 dex at M _⋆ = 10 ^9.5 M _⊙ to −0.25 dex at M _⋆ > 10 ^11 M _⊙ . That is, we find that the near-IR stellar mass–size relation for star-forming galaxies is flatter in the rest-frame near-IR than in the rest-frame optical at all redshifts 0.5 10 ^11 M _⊙ ) star-forming galaxies evolve in size almost as fast as quiescent galaxies. Low-mass ( M _⋆ < 10 ^10 M _⊙ ) quiescent galaxies evolve as slow as star-forming galaxies. Our main conclusion is that the size evolution narrative as it has emerged over the past two decades does not radically change when accessing the rest-frame near-IR with JWST, a better proxy of the underlying stellar mass distribution.

Keywords

• Galaxy evolution
• Galaxy quenching
• Galaxy structure
• Galaxy radii
• High-redshift galaxies
• Scaling relations