Non-circular motion evidence in the circumnuclear region of M100 (NGC 4321)

We analyse new integral field spectroscopy of the inner region (central 2.5 kpc) of the spiral galaxy NGC 4321 to study the peculiar kinematics of this region. Fourier analysis of the velocity residuals obtained by subtracting an axisymmetric rotation model from the Hα velocity field, indicates that the distortions are {\em global} features generated by an m=2 perturbation of the gravitational potential which can be explained by the nuclear bar. This bar has been previously observed in the near-infrared but not in the optical continuum dominated by star formation. We detect the optical counterpart of this bar in the 2D distribution of the old stellar population (inferred from the equivalent width map of the stellar absorption lines). We apply the Tremaine--Weinberg method to the stellar velocity field to calculate the pattern speed of the inner bar, obtaining a value of Ωb=160±70kms−1kpc−1. This value is considerably la rger than the one obtained when a simple bar model is considered. However the uncertainties in the pattern speed determination prevent us to give support to alternative scenarios.This paper has been supported by the ‘Plan Andaluz de Investigación’ (FQM-108) and by the ‘Secretaría de Estado de Política Científica y Tecnológica’ (AYA2000-2046-C02-01, AYA2004-08251-C02-02, ESP2004-06870-CO2-02). This research has made use of the NASA/IPAC Extragalactic Database which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We have used observations made with the NASA/ESA HST, obtained from the data archive at the Space Telescope Science Institute (STScI). STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. J. Jiménez-Vicente acknowledges support from the Consejería de Educación y Ciencia de la Junta de Andalucía. A. Castillo-Morales acknowledges the support from Universidad Complutense de Madrid (AYA2003-01676). We thank J. Knapen and A. Zurita for their help with the astrometric calibration of our images. We also acknowledge the support of the RTN Euro3D: ‘Promoting 3D spectroscopy in Europe’