Title: Evidence for a Dusty Dark Dwarf Galaxy in the Quadruple Lens MG0414+0534,
Abstract: We report the $4 \, \sigma$ detection of a faint object with a flux of ~ 0.3
mJy, in the vicinity of the quadruply lensed QSO MG0414+0534 using the Atacama
Large Millimeter/submillimeter array (ALMA) Band 7. The object is most probably
a dusty dark dwarf galaxy, which has not been detected in either the optical,
near-infrared (NIR) or radio (cm) bands. An anomaly in the flux ratio of the
lensed images observed in Band 7 and the mid-infrared (MIR) band and the
reddening of the QSO light color can be simultaneously explained if we consider
the object as a lensing substructure with an ellipticity ~ 0.7 at a redshift of
$0.5 \lesssim z \lesssim 1$. Using the best-fit lens models with three lenses,
we find that the dark matter plus baryon mass associated with the object is
$\sim 10^9\, M_{\odot}$, the dust mass is $\sim 10^7\,M_{\odot}$ and the linear
size is $\gtrsim 5\,$kpc. Thus our findings suggest that the object is a dusty
dark dwarf galaxy. A substantial portion of faint submillimeter galaxies (SMGs)
in the universe may be attributed to such dark objects.