Modeling the gas flow in the bar of NGC 1365

We present new observations of the strongly barred galaxy NGC 1365, including new photometric images and Fabry-Perot spectroscopy, as well as a detailed reanalysis of the neutral hydrogen observations from the VLA archive. We find the galaxy to be at once remarkably bisymmetric in its I-band light distribution and strongly asymmetric in the distribution of dust and in the kinematics of the gas in the bar region. The velocity field mapped in the Hα line reveals bright H II regions with velocities that differ by 60-80 km s^-1 from that of the surrounding gas, which may be due to remnants of infalling material. We have attempted hydrodynamic simulations of the bar flow to estimate the separate disk and halo masses, using two different dark matter halo models and covering a wide range of mass-to-light ratios (γ) and bar pattern speeds (Ω_p). None of our models provides a compelling fit to the data, but they seem most nearly consistent with a fast bar, corotation at ∼1.2r_B, and γ_I ≃ 2.0 ± 1.0, implying a massive, but not fully maximal, disk. The fitted dark halos are unusually concentrated, a requirement driven by the declining outer rotation curve.