The Nature of S0 Galaxies: an Unusual Case of the Isolated Lenticular Galaxy NGC 6798—a Gas Reservoir without Accretion

Abstract

We investigated the velocity field of the ionized gas and a star-formation ring in the lenticular galaxy NGC 6798 with a global counter-rotating gas disk. 3D spectroscopy data from the scanning Fabry–Perot interferometer of the 6-m BTA telescope of SAO RAS, as well as the data of narrow-band photometry in the emission lines H\(\alpha\) and [N II] \(\lambda\) 6583 from the MaNGaL mapper of the 2.5-m KGO telescope of SAI MSU were obtained and analyzed. We come to a conclusion that the case of NGC 6798 is consistent with one of the scenarios proposed earlier to explain the origin of lenticular galaxies—the orbital angular momentum of the cold outer gas accreted by the galaxy is too high, preventing it from penetrating into the central disk of the galaxy, where, being compressed by gravitation inside the stellar disk, it could begin to form stars. The weak current star formation that we did detect in NGC 6798 obviously began much later than the event of the formation of a large gas disk. The bar in the center of NGC 6798, and possibly the associated wave of radial gas contraction that we are now detecting in the ring complex of H II regions, is a consequence of a particular event in the life of the galaxy that took place no more than 1.5–2 Gyr ago.