Estimating sizes of faint, distant galaxies in the submillimetre regime
  We measure the sizes of redshift ~2 star-forming galaxies by stacking data
from the Atacama Large Millimeter/submillimeter Array (ALMA). We use a
uv-stacking algorithm in combination with model fitting in the uv-domain and
show that this allows for robust measures of the sizes of marginally resolved
sources. The analysis is primarily based on the 344 GHz ALMA continuum
observations centred on 88 sub-millimeter galaxies in the LABOCA ECDFS
Submillimeter Survey (ALESS). We study several samples of galaxies at z~2 with
$M_* \sim{} 5\times{}10^{10} $ M$_\odot$ , selected using near-infrared
photometry (distant red galaxies, extremely red objects, sBzK-galaxies, and
galaxies selected on photometric redshift).
  We find that the typical sizes of these galaxies are ~0.6 arcsec which
corresponds to ~5 kpc at z~2, this agrees well with the median sizes measured
in the near-infrared z-band (~0.6 arcsec). We find errors on our size estimates
of ~0.1-0.2 arcsec, which agree well with the expected errors for model fitting
at the given signal-to-noise ratio. With the uv-coverage of our observations
(18-160 m), the size and flux density measurements are sensitive to scales out
to 2 . We compare this to a simulated ALMA Cycle 3 dataset with intermediate
length baseline coverage, and we find that, using only these baselines, the
measured stacked flux density would be an order of magnitude fainter. This
highlights the importance of short baselines to recover the full flux density
of high-redshift galaxies.
