Using various techniques of optical observations at the 6-m Russian telescope (direct images, long-slit and 3D spectroscopy), we have studied distribution and motions of the ionized gas in the galaxy Mrk 6 having an active (Seyfert) nucleus. This lenticular galaxy is located at a distance of about 80 Mpc from us. The active galactic nuclei phenomenon is usually associated with capture of the matter by a supermassive black hole in the galactic centre. During this process, a considerable amount of energy is released in the whole range of the electromagnetic spectrum. Due to the specific spatial distribution of the gas and dust matter, the ionizing emission from the nucleus usually is collimated in two broad cones («ionization cones»).

The active nucleus of Mrk 6 is a traditional target of studies of variability in various spectral ranges; the mass of the central black hole was already measured at the 6-m SAO RAS telescope, although, deep images of the galaxy were not obtained yet.

Images obtained with the 6-m telescope using the SCORPIO and SCORPIO-2 instruments show extended filaments in the ionized-gas emission lines, despite the fact that the galaxy's stellar disc looks uniform and symmetric. The discovered filaments extend far beyond the previously known ionization cone (see the upper row of figures) up to a distance of 40 kpc from the nucleus. Observations with the scanning Fabry-Perot interferometer (see the lower row of figures) showed that the rotation of the ionized gas in the inner regions takes place in the stellar disc plane. Here the difference of the line-of-sight gas velocities from the circular rotation model do not exceed 50 km/s; although, they rise up to 250 km/s beyond the galaxy's stellar disc.

The observed velocity distribution can be explained by suggesting that the gas in the extended filaments rotate on the circular orbits almost orthogonal to the galaxy stellar disc. The study of the spectra of the filament radiation shows that the filaments gas is ionized by the active nucleus similar to that in the inner regions. The whole complex of the obtained data can be explained on the hypothesis that we observe the gas captured by Mrk 6 from the environment and illuminated by the hard radiation of the active nucleus. In this case, the active nucleus is a kind of a «searchlight» allowing the part of a considerably more extended structure of cold gas to be observed; the origin of this external cold gas is still unclear. Deep images obtained with the upgraded 1-m Schmidt telescope of the Byurakan Astrophysical Observatory of the National Academy of Sciences of Armenia demonstrate the absence of any stellar structures (tidal tails, destroyed satellites) associated with the gaseous filaments.

Published:
Smirnova A.A., Moiseev A.V., Dodonov S.N., A close look at the well-known Seyfert galaxy: extended emission filaments in Mrk 6, arXiv:1809.05950, Accepted in MNRAS

Studies are supported by the RSF grant № 17-12-01335 «Ionized gas in galactic disks and beyond the optical radius».