Optimising commensality of radio continuum and spectral line observations in the era of the SKA

TL;DR

This paper explores optimal strategies for combined HI and radio continuum surveys with the SKA to efficiently study galaxy gas content and star formation over time, highlighting their complementarity and potential for redshift measurements.

Contribution

It proposes a tiered survey strategy combining HI and continuum observations with the SKA, optimizing resource use and enhancing galaxy evolution studies.

Findings

Optimal survey parameters reduce observation time.

HI data provides redshifts for low-mass, star-forming galaxies.

Complementarity enhances galaxy evolution insights.

Abstract

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.