"Relic jet activity in “Hanny’s Voorwerp” revealed by the LOFAR Two metre Sky Survey"

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We report new observations of "Hanny's Voorwerp" (hereafter HV) taken from the second data release of the LOFAR Two-metre Sky Survey (LoTSS). HV is a highly-ionised region in the environs of the galaxy IC2497, first discovered by the Galaxy Zoo project. The new 150MHz observations are considered in the context of existing multi-frequency radio data and archival narrow-band imaging from the Hubble Space Telescope, centred on the [Oiii] emission line. The combined sensitivity and spatial resolution of the LoTSS data -- which far exceed what was previously available at radio frequencies -- reveal clear evidence for large-scale extended emission emanating from the nucleus of IC2497. The radio jet appears to have punched a hole in the neutral gas halo, in a region co-located with HV. The new 150MHz data, alongside newly-processed archival 1.64GHz eVLA data, reveal that the extended emission has a steep spectrum, implying an age $>10^8$yr. The jet supplying the extended 150MHz structure must have "turned off" long before the change in X-ray luminosity reported in recent works. In this picture, a combination of jet activity and the influence of the radiatively efficient active galactic nucleus are responsible for the unusual appearance of HV.
Original languageEnglish
Article numberstac1568
Pages (from-to)3879–3885
Number of pages7
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - 10 Jun 2022


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