Gas flow and dark matter in the inner parts of early-type barred galaxies. I. SPH simulations and comparison with the observed kinematics

This paper presents the dynamical simulations run in the potential derived from the light distribution of 5 late-type barred spiral galaxies (IC 5186, NGC 5728, NGC 7267, NGC 7483 and NGC 5505). The aim is to determine whether the mass distribution together with the hydrodynamical simulations can reproduce the observed line-of-sight velocity curves and the gas morphology in the inner regions of these barred galaxies. The light distribution is obtained from the H-band and the I-band combined. The M/L is determined using population synthesis models. The observations and the methodology of the mass distribution modelling are presented in a companion paper. The SPH models using the stellar mass models obtained directly from the H-band light distributions give a good representation of the gas distribution and dynamics of the modelled galaxies, supporting the maximum disk assumption. This result indicates that the gravitational field in the inner region is mostly provided by the stellar luminous component. When 40% of the total mass is transferred to an axisymmetric dark halo, the modelled kinematics clearly depart from the observed kinematics, whereas the departures are negligible for dark mass halos of 5% and 20% of the total mass. This result sets a lower limit for the contribution of the luminous component of about 80%, which is in agreement with the maximum disk definition of the stellar mass contribution to the rotation curve (about 85% ± 10). This result is in agreement with the results found by Weiner et al. (2001) for NGC 4123 using a similar methodology. For two galaxies, NGC 7483 and IC 5186, a very good agreement with the observed data is found. In these cases the non-circular motions can help to break the disk-halo degeneracy. For the other three galaxies (NGC 5728, NGC 7267 and NGC 5505) no definite results are found: for NGC 7267 and NGC 5505 no steady state is reached in the simulations and for NGC 5728 there is no good agreement with the observed kinematics, possibly due to the presence of a secondary bar decoupled from the primary. However, for this latter galaxy the M/L ratio used gives the right amplitude of the rotation curve, in further support of the M/L calculation method used throughout this work. Fast bars give the best fit to the observed kinematics for NGC 7483 and IC 5186 with corotation at the end of the bar for NGC 7483 and at 1.4 × Rbar for IC 5186. For NGC 5505 for which no steady state configuration is found, the addition of a rigid halo stabilises the gas flows but the derived kinematics does not fit well the observations.