Spatial extent of molecular gas, dust, and stars in massive galaxies at z=2-2.5 determined with ALMA and JWST

TL;DR

This study uses ALMA and JWST to analyze the spatial distribution of molecular gas, dust, and stars in massive galaxies at z=2-2.5, revealing insights into their star formation activity and core formation processes.

Contribution

It provides high-resolution observations comparing molecular gas, dust, and stars, and models radial gradients of star formation and gas properties in massive galaxies at high redshift.

Findings

Molecular gas extends about 60% further than dust emission.

Inner regions show higher sSFR and shorter gas depletion times.

Galaxies are likely in a phase of core formation before quenching begins.

Abstract

We present the results of 0.6"-resolution observations of CO J=3-2 line emission in 10 massive star-forming galaxies at z=2.2-2.5 with the Atacama Large Millimeter/submillimeter Array (ALMA). We compare the spatial extent of molecular gas with those of dust and stars, traced by the 870 $\mu$m and 4.4 $\mu$m continuum emissions, respectively. The average effective radius of the CO emission is 1.75$\pm$0.34 kpc, which is about 60 percent larger than that of the 870 $\mu$m emission and is comparable with that of the 4.4 $\mu$m emission. Utilizing the best-fit parametric models, we derive the radial gradients of the specific star-formation rate (sSFR), gas depletion timescale, and gas-mass fraction within the observed galaxies. We find a more intense star-formation activity with a higher sSFR and a shorter depletion timescale in the inner region than in the outer region. The central starburst may be the primary process for massive galaxies to build up a core. Furthermore, the gas-mass fraction is high, independent of the galactocentric radius in the observed galaxies, suggesting that the galaxies have not begun to quench star formation. Given the shorter gas depletion timescale in the center compared to the outer region, quenching is expected to occur in the center first and then propagate outward. We may be witnessing the observed galaxies in the formation phase of a core prior to the forthcoming phase of star formation propagating outward.