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The Tremaine-Weinberg method is a well-known model independent technique formeasuring density wave pattern speeds in spiral galaxies. Here we show how itcan be applied to the data cubes (maps of surface brightness and velocity)obtained in H-alpha emission using a Fabry-Perot spectrometer. One of the maindifficulties, the discontinuity of the H-alpha emission, is resolved using theneighbouring stellar continuum delivered by the data cube. We argue fromsymmetry that the motions not associated with the density wave should cancel.We show that our pattern speeds are reasonable by computing corotation radii,and comparing them to measured bar lengths. Simulations including star forminggas also add credibility to our results. Nevertheless it will be necessary tocompare them with results using the spectra of the stellar components toquantify any systematic deviations from valid pattern speed values.

Using the Tremaine-Weinberg method to measure pattern speeds from H\alpha velocity maps