Kinematics of ionized and molecular hydrogen in the core of M100

We present high angular and velocity resolution two-dimensional\nkinematic observations in the spectral lines of H alpha and CO J = 1 -->\n0 of the circumnuclear starburst region in the barred spiral galaxy\nM100, and compare them with kinematics derived from our previously\npublished numerical modeling. The H alpha data, fully sampled and at\nsubarcsecond resolution, show a rotation curve that is rapidly rising in\nthe central similar to 140 pc, and stays roughly constant, at the main\ndisk value, further out. Noncircular motions are studied from the H\nalpha and CO data by detailed consideration of the velocity fields,\nresidual velocity fields after subtraction of the rotation curve, and\nsets of position-velocity diagrams. These motions are interpreted as the\nkinematic signatures of gas streaming along the inner part of the bar,\nand of density wave streaming motions across a two-armed minispiral.\nComparison with a two-dimensional velocity field and rotation curve\nderived from our 1995 dynamical model shows good qualitative and\nquantitative agreement for the circular and noncircular kinematic\ncomponents. Both morphology and kinematics of this region require the\npresence of a double inner Lindblad resonance in order to explain the\nobserved twisting of the near-infrared isophotes and the gas velocity\nfield. These are compatible with the presence of a global density wave\ndriven by the moderately strong stellar bar in this galaxy. We review\nrecent observational and modeling results on the circumnuclear region in\nM100, and discuss the implications for bar structure and gas dynamics in\nthe core of M100 and other disk galaxies.