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GALAXIES

The super-resolved megamasers of NGC 4258

Nature Astronomy volume 6, pages 885–886 (2022)Cite this article

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The precise location of megamaser emission regions in galactic accretion disks has been challenging to pinpoint. Now with interferometric observations leveraging baselines larger than the Earth’s diameter, the missing information is getting closer and closer.

Writing in Nature Astronomy, Willem Baan and colleagues1 present space-based observations of the megamasers in galaxy NGC 4258 taken with interferometric baselines that span from Earth to space, achieved by the Space Radio Telescope of the RadioAstron Observatory. Three different sets of observations are presented in the paper, with increasing maximum baselines of 1.3, 9.5 and 19.5 Earth diameters, and reaching maximum angular resolutions of 11–23 microarcseconds. This provides 40–90 times better resolution than previous ground-based Very Long Baseline interferometry (VLBI) observations. With this super-resolution, Baan and colleagues show how the megamaser spectra change with the longer Earth–space baselines, revealing a pattern with velocity peaks that are spaced at regular intervals. As the megamasers are known to originate in the black hole accretion disk of NGC 4258, the authors explain the evenly spaced peaks as the result of periodic magnetorotational instabilities (MRI) inside the disk. These shear-driven instabilities are expected to grow into radial wave patterns, ultimately producing a series of ‘fingers’ of high and low angular momentum.

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Fig. 1: The megamasers in the disk of NGC 4258 seen on VLBI scales.

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  1. Leiden Observatory, Leiden, the Netherlands

    C. M. Violette Impellizzeri

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  1. C. M. Violette Impellizzeri
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Correspondence to C. M. Violette Impellizzeri.

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Impellizzeri, C.M.V. The super-resolved megamasers of NGC 4258. Nat Astron 6, 885–886 (2022). https://doi.org/10.1038/s41550-022-01764-2

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