Kavli Affiliate: John D. Silverman
| First 5 Authors: Zhaoxuan Liu, John D. Silverman, Emanuele Daddi, Boris S. Kalita, Annagrazia Puglisi
| Summary:
We present high-resolution and spatially-matched observations with JWST and
ALMA of a starburst galaxy (PACS-830) at $z=1.46$. The NIRCam observations
mainly trace the stellar light while the CO ($J$=5–4) observations map the
dense molecular gas at kpc scales. Both datasets reveal the morphology to be
that of a gas/dust rich bulge with two extending arms, together resembling a
grand-design spiral galaxy. The more pronounced arm contributes 21 $pm$ 6% of
the total CO emission. These results demonstrate that starburst activity at
high redshift can be triggered, without undergoing a highly disruptive major
merger. We assess the strength and distribution of star formation using two
tracers: (1) Polycyclic Aromatic Hydrocarbons (PAHs) emission detected at
$8~mu$m ($L_8$) with a MIRI/F1800W image, and (2) $L_mathrm{IR}$, inferred
from the CO ($J$=5–4) map. The spatial profiles of the $L_mathrm{IR}$ and
$L_8$ are dissimilar, thus leading to a significant deficit of mid-IR ($L_8$)
emission in the nucleus. We hypothesize that this is due to the destruction of
PAH molecules by the intense ionizing radiation field or decreased emission in
the photodissociation region, as seen in nearby star-forming regions and
consistent with the galaxy-wide properties of distant starbursts. This study
reveals spatial variations in the $L_8$ to $L_mathrm{IR}$ ratio for the first
time at $z>1$, in agreement with expectations from theory. Our analysis
underscores the pivotal role of joint high-resolution observations with JWST
and ALMA in discerning the different phases of the interstellar medium (ISM)
and revealing internal physics in galaxy substructures.
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