My PhD project focuses on studying gas kinematics in the centres of a sample of 23 nearby galaxies from the Composite Bulges Survey (Erwin et al. 2021) with integral-field unit observations, particularly using MUSE data. The contribution of gas inflows to the evolution of galaxies is significant, but the dominant driving mechanism for gas inflows in galactic centres and connection of gas flow to nuclear stellar components are not yet fully understood. Theoretical arguments and numerical models indicate that gas inflow occurs in coherent structures (shocks, kinematic spirals) that form in response to the stellar gravitational potential. Gas emission-line studies reveal disturbed kinematics diverging from simple circular motions, and we study unbinned kinematic maps which, together with a large FoV of MUSE, maximises the prospect of finding coherent structures. The goal of my project is to determine whether such structures provide the dominant mechanism of inflow.

To highlight the coherent structures, we fit a rotating disc to the kinematics and subtract its circular velocity. We find that the residual maps strongly depend on the parameters of the fitted disc. There are coherent structures in the residuals, but they are distorted or obscured by artefacts introduced by the fit. Here we show that comparing residuals from discs, which are fitted with different parameters, allows us to separate the true coherent residuals from the artefacts of the fit.