AGN that's shut down?

https://www.legacysurvey.org//viewer/?ra=344.5783&dec=1.1984&layer=vlass1.2&zoom=14

This is the galaxy the radio emissions seem to be centred on

Screenshot 2021-09-16 at 14.22.51

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Hmm that is odd. Best guess is some sort of extremely variable radio galaxy :man_shrugging:

…with an AGN that has recently shut down, as in the Hanny’s Voorwerp galaxy?

With Hanny’s Voorwerp, the voorwerp was still visible because it was a considerable distance from the AGN, and closer to us, so the light could still reach us from it. I’m not so sure that would be the case for radio lobes/jets. I’m don’t know if the active nucleus has shut down, or is merely extremely variable, and is currently exhibiting very little radio flux.

I guess it depends on the time domain of the variability. If the quasar flickered on and off, as some apparently do, one would expect to see bright “knots” in the jet plumes as bursts of material travel outwards over many millions of years, interspersed with more quiet periods. The radio emission here doesn’t display any knots that would indicate variable quasar activity, and the absence of a bright central emission from the galaxy “today” suggests that the source may have “recently” shut down, as in HsV. We’ll never know if it will switch on again, as these changes typically happen over many thousands of years, according to the Hubble team studying HsV.

“We just missed catching the quasar, because it turned off no more than 200,000 years ago, so what we’re seeing is the afterglow from the quasar,” Keel says. “This implies that it might flicker on and off, which is typical of quasars, but we’ve never seen such a dramatic change happen so rapidly.”