T. D. Joseph, and 55 co-authors, reported in mid-2020 that two new radio continuum images from the Australian Square Kilometer Array Pathfinder (ASKAP) survey come from the direction of the Small Magellanic Cloud (SMC). These images are part of the Evolutionary Map of the Universe (EMU) Early Science Project (ESP) survey of the Small and Large Magellanic Clouds. The two new source lists produced from these images contain radio continuum sources observed at 960 MHz (4489 sources) and 1320 MHz (5954 sources) with a bandwidth of 192 MHz and beam sizes of 30.0 × 30.0 arcsec2 and 16.3 × 15.1 arcsec2, respectively.
The median root mean square (RMS) noise values are 186 μJy beam−1 (960 MHz) and 165 μJy beam−1 (1320 MHz). To create point source catalogues, the authors used these two source lists, together with the previously published Molonglo Observatory Synthesis Telescope (MOST) and the Australia Telescope Compact Array (ATCA) point source catalogues to estimate spectral indices for the whole population of radio point sources found in the survey region. Combining our ASKAP catalogues with these radio continuum surveys, we found 7736 point-like sources in common over an area of 30 deg2.
In addition, the authors reported the detection of two new, low surface brightness supernova remnant candidates in the SMC. The high sensitivity of the new ASKAP ESP survey also enabled the authors to detect the bright end of the SMC planetary nebula sample, with 22 out of 102 optically known planetary nebulae showing point-like radio continuum emission. Lastly, we present several morphologically interesting background radio galaxies.
The authors concluded in findings that can be summarized as follows:
(i) This new ASKAP survey is a significant improvement (factor of ∼4 in the median RMS) compared to previous ATCA/MOST surveys of the SMC.
(ii) The authors identified 4,489 and 5,954 point sources at 960 and 1,320 MHz, respectively, with the majority of these sources detected above the 5σ threshold in their respective bands. They also listed non-point sources at both ASKAP frequencies 282 and 641, respectively.
(iii) Combining the two new ASKAP catalogues with other radio continuum surveys, the authors found 7,736 point-like sources in common which they listed, together with spectral indices they determined from all available survey data.
(iv) Two new low surface brightness SNR candidates were discovered, bringing the total number of SNRs and SNR candidates in the SMC to 23.
(v) Radio counterparts to 22 optically known PNe were detected. This sample of PNe is complete down to 0.6 mJy
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