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Molecular gas in the barred spiral M100 - II. 12 CO(1-0) interferometer observations and numerical simulations

Using the IRAM interferometer we have mapped at high resolution (2"x1") the 12CO(1-0) emission in the nucleus of the doubled barred SABbc spiral M100. Molecular gas is distributed in a two spiral arm structure starting from the end points of the nuclear bar (r=600 pc) and a central source. The kinematics of the gas indicates the existence of a steep rotation curve (180 km/s at 100 pc) and strong streaming motions characteristic of a trailing spiral wave inside corotation. Gas flow simulations analyse the gas response to a gravitational potential derived from the K-band plate, including the two nested bars. We develop two families of models: first, a single pattern speed solution shared by the outer bar+spiral and by the nuclear bar, and secondly, a two independent bars solution, where the nuclear bar is dynamically decoupled and rotates faster than the primary bar. We found the best fit solution consisting of a fast pattern (160 km/s/kpc) for the nuclear bar (with corotation at 1.2 kpc) decoupled from the slow pattern of the outer bar+spiral (23 km/s/kpc, with corotation at 8-9 kpc).