Bar diagnostics in edge-on spiral galaxies. II. Hydrodynamical simulations

We develop diagnostics based on gas kinematics to identify the presence of a bar in an edge-on spiral galaxy and determine its orientation. We use pos ition-velocity diagrams (PVDs) obtained by projecting edge-on two-dimension al hydrodynamical simulations of the gas flow in a barred galaxy potential. We show that when a nuclear spiral is formed, the presence of a gap in the PVDs, between the signature of the nuclear spiral and that of the outer pa rts of the disk, reliably indicates the presence of a bar. This gap is due to the presence of shocks and inflows in the simulations, leading to a depl etion of the gas in the outer bar region. If no nuclear spiral signature is present in a PVD, only indirect arguments can be used to argue for the pre sence of a bar. The shape of the signature of the nuclear spiral, and to a lesser extent that of the outer bar region, allows a determination of the o rientation of the bar with respect to the line of sight. The presence of du st can also help to discriminate between viewing angles on either side of t he bar. Simulations covering a large fraction of parameter space constrain the bar properties and mass distribution of observed galaxies. The stronges t constraint comes from the presence or absence of the signature of a nucle ar spiral in the PVD.