JWST+ALMA reveal the build up of stellar mass in the cores of dusty star-forming galaxies at Cosmic Noon

Abstract

Dusty star-forming galaxies have long been suspected to serve as the missing evolutionary bridge between the star-forming and quiescent phases of massive galaxy evolution. With the combined power of JWST and ALMA, it is now possible to use high resolution imaging at rest-frame ultraviolet (UV), optical, near-infrared (NIR), and sub-mm wavelengths to study the multi-wavelength morphologies tracing both the stellar populations and dust during this key phase. We present the joint analysis of JWST/NIRCam imaging in GOODS-S and mm dust emission traced by ALMA for a sample of 33 galaxies at $z=1.5$ to $z=5.5$ selected from the 1.1mm GOODS-ALMA 2.0 survey, and compare the morphologies of this population to mass- and redshift-selected samples of field star-forming and quiescent galaxies. The 1.1mm-selected sample is morphologically distinct from other similarly massive star-forming galaxies; we find a steeper size-wavelength gradient from 1.5-4.4$μ$m, with a more dramatic decrease in size towards longer wavelengths. While the rest-NIR surface brightness profiles of the 1.1mm-selected galaxies are brighter in the inner regions relative to the field star-forming population, they are remarkably similar to the quiescent population. These morphological differences could suggest that dusty star-forming galaxies, unlike more typical star-forming galaxies, have already built up stellar mass in a severely dust-obscured core, leading to extended and clumpy morphologies at rest-UV and rest-optical wavelengths and more compact emission in the rest-NIR that is co-spatial with dust. If the bulge is already established, we speculate that mm-selected galaxies may imminently evolve to join their quiescent descendants.

Figures (11)

• Figure 1: The stellar mass and redshift of the 1.1mm-selected GOODS-ALMA sample (white points), with field galaxies (with a stellar mass of log(M/M$_\odot) >$ 10 shown in gray contours. The mass and redshift selections for GOODS-S field galaxies is described in Section \ref{['sec:nircam']}.
• Figure 2: SFRs obtained through SED fitting with UV-NIR data alone (purple squares) are systematically lower at a given stellar mass than from SED fitting that incorporates the mid-IR to mm gomezguijarro2022b. We also plot the star-forming main sequence relations from leja2022 (dashed black line) and whitaker2014 (blue dashed line), where shaded regions assume 0.25 dex scatter in the main sequence, as well as GOODS-S field galaxies (gray points) at $1<z<5.5$.
• Figure 3: The effective radius along the semi-major axis at a given mass is larger in 1.5$\mu$m (left) and smaller in 4.4$\mu$m sizes (right) for 1.1mm-selected sample (gray points) relative to the field sample of star-forming galaxies described in Section \ref{['sec:nircam']} (blue contours). The average size-mass relation for the field sample are the solid blue lines. In 4.4$\mu$m, the 1.1mm-selected sample aligns with the quiescent population described in Section \ref{['sec:nircam']} (red contours). Size-mass relations from the literature in the rest-optical vanderwel2014 and rest-NIR martorano2024 are shown as blue (star-forming) and red (quiescent) dashed lines. The shading of 1.1-mm selected galaxies is based on redshift. Out of 22 galaxies that are detected in 1.5$\mu$m, the 14 points shown represent those with good fits as determined by GALFIT.
• Figure 4: A direct comparison of effective radius measured at 1.5$\mu$m vs at 4.4$\mu$m shows that the 1.1-mm selected sample are unusually large in 1.5$\mu$m relative to 4.4$\mu$m. Blue contours are the 20th, 50th, and 80th percentiles of the distribution of the field sample (blue points). The shading of 1.1-mm selected galaxies is based on redshift.
• Figure 5: Bright red cores are visible in 3.2$\hbox{$^{\prime\prime}$}$ by 3.2$\hbox{$^{\prime\prime}$}$ RGB stamps of the ALMA-selected sample, where the false color images combine the 1.5$\mu$m, 2.7$\mu$m, and 4.4$\mu$m NIRCam bands with 2$\sigma$, 4$\sigma$, and 6$\sigma$ contours from ALMA mm observations in white. The ALMA beam size is shown in the bottom right corner of each stamp. Galaxies are separated into three groups depending on whether they are not classified as a merger (left), their merger status is ambiguous (center), or they are classified as a merger according to their Gini/M20 parameters in 1.5$\mu$m Lotz2004Lotz2008. Within these groups, galaxies are sorted from the top down by increasing asymmetry parameter.