Retrograde infall of the intergalactic gas onto S-galaxy and activity of galactic nuclei

Abstract We present the results of numerical simulations focused on the accretion of intergalactic gas onto a gas-rich S-type disc galaxy. Our investigation explores the conditions favouring the emergence of counterrotating stellar and gaseous components within the galaxy, leading to the inflow of gas towards the central kiloparsec of the galaxy. Notably, we find that the most substantial reservoir of gas, serving as fuel for galactic nucleus activity, resides within the central region during the retrograde infall of gas at an incident angle of approximately 2 0 ° 2{0}^{^\circ } relative to the galactic plane. Departures from this angle significantly diminish the gas flow rate towards the galactic centre. Conversely, the prograde infall of intergalactic gas makes a marginal contribution to the gas content in the central region and cannot supply fuel to the active galactic nucleus. An intriguing characteristic of the observed retrograde impact is the emergence of a rotating polar ring at the galaxy’s periphery, primarily originating from intergalactic gas.