Abstract
Exploiting the sensitivity and spatial resolution of the Atacama Large
Millimeter/submillimeter Array (ALMA), we have studied the morphology and the
physical scale of the interstellar medium - both gas and dust - in SGP38326, an
unlensed pair of interacting starbursts at $z= 4.425$. SGP38326 is the most
luminous star bursting system known at $z > 4$ with an IR-derived $SFR
4300 \, M_\, yr^-1$. SGP38326 also contains a molecular gas
reservoir among the most massive ever found in the early Universe, and it is
the likely progenitor of a massive, red-and-dead elliptical galaxy at $z \sim
3$. Probing scales of $0.1"$ or $800 \, pc$ we find that the
smooth distribution of the continuum emission from cool dust grains contrasts
with the more irregular morphology of the gas, as traced by the CII fine
structure emission. The gas is also extended over larger physical scales than
the dust. The velocity information provided by the resolved CII emission
reveals that the dynamics of the two components of SGP38326 are compatible with
disk-like, ordered rotation, but also reveals an ISM which is turbulent and
unstable. Our observations support a scenario where at least a subset of the
most distant extreme starbursts are highly dissipative mergers of gas-rich
galaxies.
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