Lopsided gas discs arising from mass inflow in barred spiral galaxies

We explore numerically the effects of mass inflow on barred spiral galaxies in the context of high-velocity clouds accreting on to galactic discs. To assess whether such events are detectable, we quantify their effect on the disc's gas distribution by calculating the lopsidedness parameter A(1), and by deriving position-velocity plots of HI emission. The impact of an accretion event strongly depends on the parameters of the high-velocity cloud. For cloud mass >= 10(7) M-circle dot, infall can have a lasting impact on the gaseous disc, with A(1) greater than or similar to 0.05 for similar to 1.5 Gyr. We discuss the time-variability of the lopsidedness parameter and consequences for detecting gas infall. Accretion events will be marginally noticeable in position-velocity diagrams, again depending on cloud parameters. Our models provide a possible explanation for low-amplitude lopsidedness observed in galaxies without nearby companions.