1996A&A...313...65L

We perform two-dimensional, time dependent, hydrodynamical simulations of the gas flow in a potential representing the barred spiral galaxy NGC 1365 using the FS2 code originally written by G.D. van Albada. Non-circular motions present in NGC 1365 prevent us from using an observed angle-averaged rotation curve as representative of the axisymmetric forces in the bar region. Comparing observed kinematics and gas features in NGC 1365 with corresponding quantities in the models enables us to estimate a possible representation of the true axisymmetric forces. We compute models perturbed by a pure bar potential and models perturbed by a bar + spiral potential. A J-band image is used to estimate the bar potential under the assumption of a constant M/L_J ratio. The spiral potential is determined from the same image and has the same pattern speed as the bar, but is not assumed to have necessarily the same M/L_ J_ ratio. We find good agreement between observations and models, both concerning the HI and CO density distribution and the velocity field. Using just the shape of the observed bar potential we drive the main spiral features out to the required radius. Our best fitting bar model has a pattern speed of {OMEGA}_p=20km/s/kpc placing corotation at a distance R_CR∼145"=1.21R_bar, where R_bar is the optical semimajor axis of the bar. The offset dust lanes observed in optical images are reproduced by the models provided the latter have an inner Lindblad resonance at a radius of ∼27". Steep velocity gradients across the dust lanes and spiral arms are seen in both model and observations. Most observed features are reproduced in the models, and the general streaming motions are in qualitative agreement with linear gas orbit theory. Contrary to observations, the pure bar perturbed models cannot drive an inner arm across corotation. Models having both a bar and spiral perturbing potential reduce this problem, thus suggesting the existence of massive spiral arms in NGC 1365. Our best fitting bar + spiral model has a pattern speed of {OMEGA}_p=18km/s/kpc placing corotation at a distance R_CR∼157"=1.31R_bar