  Galaxy mergers play a critical role in galaxy evolution - altering the size,
morphology, dynamics and composition of galaxies. So far, galaxy mergers have
mostly been identified through visual inspection of their rest-frame optical
and NIR emission. But, dust can obscure this emission, resulting in the
misclassification of mergers as single galaxies, and the incorrect
interpretation of their baryonic properties. Having serendipitously discovered
a dust-obscured galaxy merger at z = 1.17, we aim to determine the baryonic
properties of the two merging galaxies, including the star formation rate, and
stellar, molecular gas, and dust masses. Using Band 3 and 6 observations from
the Atacama Large Millimeter and submillimeter Array (ALMA), and ancillary
data, we study the morphology of this previously misclassified merger. We
deblend the emission, derive the gas masses from CO observations, and model the
spectral energy distributions, to determine the properties of each galaxy.
Using the rare combination of ALMA CO(2-1), CO(5-4) and dust-continuum
(rest-frame 520um) observations, we provide insights into the gas and dust
content and ISM properties of each merger component. We find that only one of
the two galaxies is highly dust-obscured, whereas both are massive (> 10^10.5
Msun), highly star-forming (SFR = 60-900Msun/yr), have a moderate-to-low
depletion time (tdepl < 0.7Gyr) and high gas fraction ( fgas >= 1). These
properties can be interpreted as the positive impact of the merger. With this
serendipitous discovery, we highlight the power of (sub)millimeter observations
to identify and characterise the individual components of obscured galaxy
mergers.
