JWST Reveals Bulge-dominated Star-forming Galaxies at Cosmic Noon

TL;DR

Using JWST's high-resolution imaging, this study reveals that massive star-forming galaxies at cosmic noon have dense bulge-like cores in their centers, which are key to understanding galaxy quenching processes.

Contribution

First demonstration of JWST's ability to map stellar mass distribution in high-redshift galaxies, revealing bulge-dominated cores in star-forming galaxies at z~2.

Findings

Massive star-forming galaxies are more bulge-dominated in near-infrared than optical.

Central surface density correlates with galaxy quenching status.

High central densities are present during star formation, influencing galaxy evolution.

Abstract

Hubble Space Telescope imaging shows that most star-forming galaxies at cosmic noon -- the peak of cosmic star formation history -- appear disk-dominated, leaving the origin of the dense cores in their quiescent descendants unclear. With the James Webb Space Telescope's (JWST) high-resolution imaging to 5 {\mu}m, we can now map the rest-frame near-infrared emission, a much closer proxy for stellar mass distribution, in these massive galaxies. We selected 70 star-forming galaxies with 10$<$log(M)$<$12 and 1.5$<$z$<$3 in the CEERS survey and compare their morphologies in the rest-frame optical to those in the rest-frame near-IR. While the bulk of these galaxies are disk-dominated in 1.5 {\mu}m (rest-frame optical) imaging, they appear more bulge-dominated at 4.4 {\mu}m (rest-frame near-infrared). Our analysis reveals that in massive star-forming galaxies at z$\sim$2, the radial surface brightness profiles steepen significantly, from a slope of $\sim$0.3/dex at 1.5 {\mu}m to $\sim$1.4/dex at 4.4 {\mu}m within radii $<$ 1 kpc. Additionally, we find their total flux contained within the central 1 kpc is approximately 7 times higher in F444W than in F150W. In rest-optical emission, a galaxy's central surface density appears to be the strongest indicator of whether it is quenched or star-forming. Our most significant finding is that at redder wavelengths, the central surface density ratio between quiescent and star-forming galaxies dramatically decreases from $\sim$10 to $\sim$1. This suggests the high central densities associated with galaxy quenching are already in place during the star-forming phase, imposing new constraints on the transition from star formation to quiescence.