Optimising commensality of radio continuum and spectral line
  observations in the era of the SKA
  The substantial decrease in star formation density from z=1 to the present
day is curious given the relatively constant neutral gas density over the same
epoch. Future radio astronomy facilities, including the SKA and pathfinder
telescopes, will provide pioneering measures of both the gas content of
galaxies and star formation activity over cosmological timescales. Here we
investigate the commensalities between neutral atomic gas (HI) and radio
continuum observations, as well as the complementarity of the data products. We
start with the proposed HI and continuum surveys to be undertaken with the SKA
precursor telescope MeerKAT, and building on this, explore optimal combinations
of survey area coverage and depth of proposed HI and continuum surveys to be
undertaken with the SKA1-MID instrument. Intelligent adjustment of these
observational parameters results in a tiered strategy that minimises
observation time while maximising the value of the dataset, both for HI and
continuum science goals. We also find great complementarity between the HI and
continuum datasets, with the spectral line HI data providing redshift
measurements for gas-rich, star-forming galaxies with stellar masses
Mstellar~10^9 Msun to z~0.3, a factor of three lower in stellar mass than would
be feasible to reach with large optical spectroscopic campaigns.
