This paper is an overview by the Extragalactic Continuum Science Working Group of the SKAO. It explains how deep, wide and multi-band radio continuum observations with the SKAO’s telescopes can reveal the energetic processes that drive galaxy evolution. The authors summarize planned science goals and show how the SKAO’s combination of sensitivity, angular resolution and survey speed can open new windows on star formation, accretion onto supermassive black holes, magnetic fields and cosmic rays in galaxies and large-scale structures.

The group organizes these goals around several approaches. They will run wide-area continuum surveys to build large, unbiased samples. They will also use multi-band observations and deep imaging in fields that already have lots of data at other wavelengths. Combining SKA-Low and SKA-Mid data gives coverage across roughly three orders of magnitude in frequency (about 10 MHz to 10 GHz), which helps separate different radio emission processes.

At a basic level, radio continuum emission comes from two main mechanisms: synchrotron emission, produced when fast charged particles spiral in magnetic fields, and free-free emission, produced by hot ionized gas. Together these components can trace star formation in a way that is not affected by dust. Multi-band radio spectral energy distributions (SEDs) — the brightness of a source as a function of frequency — can be used to separate the thermal and non-thermal parts and to estimate star-formation rates without relying only on infrared measurements.

The paper highlights concrete expected gains. SKA-Low and SKA-Mid will be much faster than current facilities. For example, about 1 hour with SKA-Low at a reference sensitivity is expected to reach depths comparable to LOFAR Deep Fields that used roughly 100 hours. Ten minutes with SKA-Mid (Band 2) should improve on the depth of the MIGHTEE survey, and Band 5 observations might match COSMOS-XS depth in about one tenth of the time. The authors cite modelling that suggests a reference survey could detect of order 1.5×10^4 star-forming galaxies in all bands out to redshift z ≃ 7.