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
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).
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.
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
Contact - Moiseev A.V.,
DSc, Leading Researcher in the laboratory of spectroscopy
and photometry of extragalactic objects
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
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).