JWST and ALMA discern the assembly of structural and obscured components in a high-redshift starburst galaxy

Kavli Affiliate: John D. Silverman

| First 5 Authors: Zhaoxuan Liu, John D. Silverman, Emanuele Daddi, Annagrazia Puglisi, Alvio Renzini

| Summary:

We present observations and analysis of the starburst, PACS-819, at z=1.45
($M_*=10^{10.7}$ M$_{ odot}$), using high-resolution ($0^{prime prime}.1$;
0.8 kpc) ALMA and multi-wavelength JWST images from the COSMOS-Web program.
Dissimilar to HST/ACS images in the rest-frame UV, the redder NIRCam and MIRI
images reveal a smooth central mass concentration and spiral-like features,
atypical for such an intense starburst. Through dynamical modeling of the CO
J=5–4 emission with ALMA, PACS-819 is rotation-dominated thus has a disk-like
nature. However, kinematic anomalies in CO and asymmetric features in the bluer
JWST bands (e.g., F150W) support a more disturbed nature likely due to
interactions. The JWST imaging further enables us to map the distribution of
stellar mass and dust attenuation, thus clarifying the relationships between
different structural components, not discernable in the previous HST images.
The CO J = 5 — 4 and FIR dust continuum emission are co-spatial with a
heavily-obscured starbursting core (<1 kpc) which is partially surrounded by
much less obscured star-forming structures including a prominent arc, possibly
a tidally-distorted dwarf galaxy, and a clump, either a sign of an ongoing
violent disk instability or a recently accreted low-mass satellite. With
spatially-resolved maps, we find a high molecular gas fraction in the central
area reaching $sim3$ ($M_{text{gas}}$/$M_*$) and short depletion times
($M_{text{gas}}/SFRsim$ 120 Myrs) across the entire system. These
observations provide insights into the complex nature of starbursts in the
distant universe and underscore the wealth of complementary information from
high-resolution observations with both ALMA and JWST.

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