ALMA resolves molecular clouds in the metal poor Magellanic Bridge A
  (Abridged)We characterize gas and dust emission in Magellanic Bridge A, which
has the highest 870$\mu$m excess of emission found in single dish surveys.
Using the ALMA telescope, we mapped the Magellanic Bridge A molecular cloud
with sub-parsec resolution, in 1.3 mm continuum and CO(2-1) line emission. We
also map the cloud in 870$\mu$m continuum and CO(2-1) line emission at ~6 pc
resolution with APEX. We combine the ALMA and APEX CO(2-1) line cubes to study
the molecular gas emission. Magellanic Bridge A breaks up into two distinct
molecular clouds in dust and CO(2-1) emission, which we call North and South.
Dust emission in the North source, according to our best parameters from
fitting the far-infrarred fluxes, is ~3 K colder than in the South source in
correspondence to its less developed star formation. Both dust sources present
large submillimeter excesses in LABOCA data: according to our best fits the
excess over the modified blackbody (MBB) fit to the Spitzer/Herschel continuum
are ~7 and ~3 for the North and South sources respectively. Nonetheless, we do
not detect the corresponding 1.3 mm continuum with ALMA. Our limits are
compatible with the extrapolation of the MBB fits and therefore we cannot
independently confirm the excess at this longer wavelength. The CO(2-1)
emission is in two parsec-sized clouds with virial masses around 400 and 700 Mo
each. Their volume densities are ~700-2600 cm$^{-3}$, larger than typical bulk
densities of Galactic molecular clouds. The CO-to-H2 conversion factor is 6.5
and 15 M$_{\odot}$ (K km s$^{-1}$ pc$^2$)$^{-1}$ for the North and South
clouds, calculated using their respective virial masses and CO(2-1)
luminosities. Gas mass estimates from our MBB fits to dust emission yields
masses $M\sim1.3\times10^3$ M$_{\odot}$ and $2.9\times10^3$ M$_{\odot}$ for
North and South respectively, a factor ~4 larger than the virial masses we
infer from CO.
