EMU is a wide-field radio continuum survey planned for the new Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The primary goal of EMU is to make a deep (rms ,10 mJy/beam) radio continuum survey of the entire Southern sky at 1.3 GHz, extending as far North as þ308 declination, with a resolution of 10 arcsec. EMU is expected to detect and catalogue about 70 million galaxies, including typical star-forming galaxies up to z , 1, powerful starbursts to even greater redshifts, and active galactic nuclei to the edge of the visible Universe. It will undoubtedly discover new classes of object. This paper defines the science goals and parameters of the survey, and describes the development of techniques necessary to maximise the science return from EMU.

The Evolutionary Map of the Universe (EMU) is a proposed radio continuum survey of the Southern Hemisphere up to declination +30• , with the Australian Square Kilometre Array Pathfinder (ASKAP). EMU will use an automated source identification and measurement approach that is demonstrably optimal, to maximise the reliability and robustness of the resulting radio source catalogues. As a step toward this goal we conducted a "Data Challenge" to test a variety of source finders on simulated images. The aim is to quantify the accuracy and limitations of existing automated source finding and measurement approaches. The Challenge initiators also tested the current ASKAPsoft source-finding tool to establish how it could benefit from incorporating successful features of the other tools. As expected, most finders show completeness around 100% at ≈10 σ dropping to about 10% by ≈5 σ . Reliability is typically close to 100% at ≈10 σ , with performance to lower sensitivities varying between finders. All finders show the expected trade-off, where a high completeness at low signal-to-noise gives a corresponding reduction in reliability, and vice versa. We conclude with a series of recommendations for improving the performance of the ASKAPsoft source-finding tool.

Star‐forming galaxies are thought to dominate the sub‐mJy radio population, but recent work has shown that low‐luminosity active galactic nuclei (AGNs) can still make a significant contribution to the faint radio source population. Spectral indices are an important tool for understanding the emission mechanism of the faint radio sources. We have observed the extended Chandra Deep Field South at 5.5 GHz using a mosaic of 42 pointings with the Australia Telescope Compact Array. Our image reaches an almost uniform sensitivity of ∼12 μJy rms over 0.25 deg2 with a restoring beam of 4.9 arcsec × 2.0 arcsec, making ATLAS 5.5 GHz survey one of the deepest 6 cm surveys to date. We present the 5.5 GHz catalogue and source counts from this field. We take advantage of the large amount of ancillary data in this field to study the 1.4 to 5.5 GHz spectral indices of the sub‐mJy population. For the full 5.5 GHz selected sample we find a flat median spectral index, αmed = −0.40, which is consistent with previous results. However, the spectral index appears to steepen at the faintest flux density levels (S5.5 GHz < 0.1 mJy), where αmed = −0.68. We performed stacking analysis of the faint 1.4 GHz selected sample (40