We present 0.″15 (1 kpc) resolution ALMA observations of the [C
II] 157.74 μm line and rest-frame 160 μm continuum emission in two
z ∼ 3 dusty, star-forming galaxies—ALESS 49.1 and ALESS 57.1,
combined with resolved CO (3–2) observations. In both sources, the
[C II] surface brightness distribution is dominated by a compact core
≤1 kpc in radius, a factor of 2–3 smaller than the extent of
the CO (3–2) emission. In ALESS 49.1, we find an additional
extended (8 kpc radius), low surface brightness [C II] component. Based
on an analysis of mock ALMA observations, the [C II] and 160 μm
continuum surface brightness distributions are inconsistent with a
single-Gaussian surface brightness distribution with the same size as
the CO (3–2) emission. The [C II] rotation curves flatten at
≃2 kpc radius, suggesting that the kinematics of the central
regions are dominated by a baryonic disk. Both galaxies exhibit a strong
[C II]/far-IR (FIR) deficit on 1 kpc scales, with FIR surface brightness
to [C II]/FIR slope steeper than in local star-forming galaxies. A
comparison of the [C II]/CO (3–2) observations with
photodissociation region models suggests a strong far-UV (FUV) radiation
field (G 0 ∼ 104) and high gas density (n(H)
∼ 104–105 cm‑3) in the
central regions of ALESS 49.1 and ALESS 57.1. The most direct
interpretation of the pronounced [C II]/FIR deficit is a thermal
saturation of the C+ fine-structure levels at temperatures
≥500 K, driven by the strong FUV field.