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Search for "Hibernating" Active Galactic Nuclei by their

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    Now there is no doubt that the activity of galactic nuclei is associated with a central supermassive black hole. The matter captured by the black hole forms a rotating accretion disk. Due to friction, the gas in the disk is heated to high temperatures and emits in a wide wavelength range. Also, it produces the ultraviolet emission capable of ionizing interstellar and intergalactic gas at a great distance from the nucleus. The specific feature of the absorbing matter distribution in the galactic nucleus (the "dusty torus") leads to the collimation of the ionizing emission along the disk axis in the form of two symmetrical wide cones. Investigation of the state of gaseous clouds outside galaxies allows us to study the emission intensity variations associated with such ionization cones, and hence, the history of the activity of a supermassive black hole.
    For the first time, such clouds have been searched for in a complete luminosity-limited sample of nearby galaxies with active nuclei. Among 111 objects, the ionized gas systems far from the nucleus (25-75 kpc) were found in the galaxies NGC235 and NGC5514. At the same time, it was found that the activity in NGC5514 more than 3 times decreased over the past 250 thousand years. Also, giant (up to 10 kpc) ionization cones inside galactic disks were found in 4 galaxies: IC1481, ESO362-G08, NGC5514, and NGC7679.
    It is shown that in the overwhelming majority, the outer ionized clouds belong to tidal structures associated with interactions of galaxies. Such clouds in the [OIII] emission line are found in 10% of all active galaxies with tidal structures noticeable in wide optical filters. Here, the gas leaves the plane of the main stellar disk and is ejected into the intergalactic space. Or, on the contrary, we are talking about the gravitational capture of the outer matter that successfully fell into the radiation cone of the active nucleus. This explains why the clouds are at such great distances from their "ancestors".
    The search for candidates was carried out using the 1-m SARA telescopes at the Kitt Peak and La Palma. The state of the gas ionization was studied with the 6-m SAO RAS telescope, the 2.5-m telescope of the Caucasian Mountain Observatory of SAI MSU, and the 1.6-m AZT-33IK telescope of ISTP SB RAS using the instruments created at SAO RAS (SCORPIO-1, SCORPIO-2, MaNGaL, and ADAM).
Fig.1. Optical image of the interacting system of the galaxies NGC 5514 from the DESI. The green color shows the emission distribution in the ionized oxygen line according to the observations with the MaNGaL instrument at the 2.5-m SAI MSU telescope. The gas illuminated by the active nucleus is visible far beyond the disks of galaxies, inside the tidal arm. The box shows the spectrum of clouds obtained with the 6-m SAO RAS telescope using the SCORPIO-2 instrument. The lines of the ionized oxygen and helium are visible confirming the gas ionization by the active nucleus.
Fig.2. Optical image of the galaxy NGC 7679 from the DESI. The green color shows the emission distribution in the ionized oxygen line according to the observations with the SCORPIO-2 at the SAO RAS 6-m telescope. The active nucleus illuminates the gas inside the galaxy. The box shows the spectrum of clouds obtained with the 6-m SAO RAS telescope using the SCORPIO-2 instrument

Published:
Keel W.C., Moiseev A., Kozlova D.V., Ikhsanova A.I., Oparin D.V., Uklein R.I., Smirnova A.A.., Eselevich M.V. The TELPERION survey for distant [O III] clouds around luminous and hibernating AGN , 2022, Monthly Notices of the Royal Astronomical Society, Volume 510, Issue 3, pp.4608-4625

Contact - Moiseev A.V., DSc, Leading Researcher in the laboratory of spectroscopy and photometry of extragalactic objects
This work was supported by RSF grant No. 17-12-01335 "Ionized gas in galactic disks and beyond the optical radius" (the RSF press release).