ASKAP–EMU radio continuum detection of planetary nebula NGC 5189: the “Infinity” nebula

Asher, A. D.; Smeaton, Z. J.; Filipović, M. D.; Hopkins, A. M.; van Loon, J. Th.; Galvin, T. J.; Barnes, L. A.

Abstract

We report the radio continuum detection of well known Galactic Planetary Nebula (PN) NGC5189, observed at 943MHz during the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey. Two detections of NGC5189 have been made during the survey, of better resolution than previous radio surveys. Both measurements of the integrated flux density are consistent with each other, at S943 MHz = 0.33 ± 0.03 Jy, and the spectral luminosity is L943 MHz = 8.89 × 1013 W m–2 Hz–1. Using available flux density measurements for radio-detections of NGC5189, we calculate a radio surface brightness at 1GHz and measure Σ1 GHz = 6.0 × 10–21 W m–2 Hz–1 sr–1, which is in the expected range for Galactic PNe. We measure an apparent size of 3.′4×2.′2 corresponding to physical diameters of 1.48 pc × 0.96 pc, and combine available radio observations of NGC5189 to estimate a spectral index of α = 0.12 ± 0.05. Hence, we agree with previous findings that NGC5189 is a thermal (free–free) emitting nebula. Additional measurements of the optical depth (τ = 0.00246) and electron density (Ne = 138 cm–3) support our findings that NGC5189 is optically thin at 943 MHz. Furthermore, the radio contours from the ASKAP–EMU image have been overlaid onto a Hubble Space Telescope (HST) Wide Field Camera 3 image, demonstrating that the radio morphology closely traces the optical. Notably, the contour alignment for the innermost region highlights the two envelopes of gas previously reported to be low-ionisation structures, which is considered a defining feature of post common–envelope PNe that surround a central Wolf-Rayet star.

Citation

Asher, A. D., Smeaton, Z. J., Filipović, M. D., Hopkins, A. M., van Loon, J. T., Galvin, T. J., & Barnes, L. A. (in press). ASKAP–EMU radio continuum detection of planetary nebula NGC 5189: the “Infinity” nebula. Publications of the Astronomical Society of Australia, 1-9. https://doi.org/10.1017/pasa.2025.10058

• Journal Article Type: Article
• Acceptance Date: Jun 24, 2025
• Online Publication Date: Jun 24, 2025
• Deposit Date: Aug 13, 2025
• Journal: Publications of the Astronomical Society of Australia
• Print ISSN: 1323-3580
• Electronic ISSN: 1448-6083
• Publisher: Cambridge University Press
• Peer Reviewed: Peer Reviewed
• Pages: 1-9
• DOI: https://doi.org/10.1017/pasa.2025.10058
• Public URL: https://keele-repository.worktribe.com/output/1365999
• Publisher URL: https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/askapemu-radio-continuum-detection-of-planetary-nebula-ngc-5189-the-infinity-nebula/C9E2535E84157452655C3C69EC246391