HerMES: ALMA Imaging of Herschel-selected Dusty Star-forming Galaxies
  The Herschel Multi-tiered Extragalactic Survey (HerMES) has identified large
numbers of dusty star-forming galaxies (DSFGs) over a wide range in redshift. A
detailed understanding of these DSFGs is hampered by the limited spatial
resolution of Herschel. We present 870um 0.45" resolution imaging from the
Atacama Large Millimeter/submillimeter Array (ALMA) of 29 HerMES DSFGs with
far-infrared (FIR) flux densities in between the brightest of sources found by
Herschel and fainter DSFGs found in ground-based sub-millimeter (sub-mm)
surveys. We identify 62 sources down to the 5-sigma point-source sensitivity
limit in our ALMA sample (sigma~0.2mJy), of which 6 are strongly lensed
(showing multiple images) and 36 experience significant amplification (mu>1.1).
To characterize the properties of the ALMA sources, we introduce and make use
of uvmcmcfit, a publicly available Markov chain Monte Carlo analysis tool for
interferometric observations of lensed galaxies. Our lens models tentatively
favor intrinsic number counts for DSFGs with a steep fall off above 8mJy at
880um. Nearly 70% of the Herschel sources comprise multiple ALMA counterparts,
consistent with previous research indicating that the multiplicity rate is high
in bright sub-mm sources. Our ALMA sources are located significantly closer to
each other than expected based on results from theoretical models as well as
fainter DSFGs identified in the LABOCA ECDFS Submillimeter Survey. The high
multiplicity rate and low projected separations argue in favor of interactions
and mergers driving the prodigious emission from the brightest DSFGs as well as
the sharp downturn above S_880=8mJy.
