Retrograde fall of intergalactic gas onto the S-galaxy: polar rings and activity of galactic nuclei

The dynamics of intergalactic gas accretion in a gas-rich spiral galaxy has been studied. We use numerical simulations to determine the conditions that lead to the formation of counter-rotating stellar and gas components within the galaxy and promote the influx of gas into the central part of the galaxy with a radius of less than one kiloparsec. The focus is on the dynamic interaction between the intergalactic flow and the gas-rich disc galaxy. The study of the mechanism by which gas is supplied to the central region to fuel the activity of galactic nuclei is a critical part of our work. The retrograde fall of the gas forms a massive, concentrated gas halo at the center of the galaxy, which may provide fuel for the activity of galactic nuclei. An angle of incidence of the gas flow of about 20 degrees to the galactic plane is the most effective and provides maximum gas concentration. Deviations from this angle lead to a decrease in the velocity of the gas flow into the galactic center. The prograde infall of intergalactic gas is incapable of cardinal disruption of the disc and does not result in an effective inflow of gas within 1 kpc radius. This accretion mode provides 100 times less gas mass within the 1 kpc radius compared to retrograde infall. An important additional result of retrograde accretion is the appearance of rotating gas rings at the periphery of the galaxy, which are mainly formed by falling intergalactic gas. The inclination of these rings with respect to the galactic plane varies widely, from 10 to 90 degrees, and depends on the angle of incidence of the intergalactic gas. The numerical simulations of counter-rotating stellar-gas discs cover all stages of the interaction with the falling intergalactic flow over a period of about 7 billion years.