Kinematics of Ionized and Molecular Hydrogen in the Core of M100

Abstract

We present high angular and velocity resolution two-dimensionalkinematic observations in the spectral lines of H alpha and CO J = 1 -->0 of the circumnuclear starburst region in the barred spiral galaxyM100, and compare them with kinematics derived from our previouslypublished numerical modeling. The H alpha data, fully sampled and atsubarcsecond resolution, show a rotation curve that is rapidly rising inthe central similar to 140 pc, and stays roughly constant, at the maindisk value, further out. Noncircular motions are studied from the Halpha and CO data by detailed consideration of the velocity fields,residual velocity fields after subtraction of the rotation curve, andsets of position-velocity diagrams. These motions are interpreted as thekinematic signatures of gas streaming along the inner part of the bar,and of density wave streaming motions across a two-armed minispiral.Comparison with a two-dimensional velocity field and rotation curvederived from our 1995 dynamical model shows good qualitative andquantitative agreement for the circular and noncircular kinematiccomponents. Both morphology and kinematics of this region require thepresence of a double inner Lindblad resonance in order to explain theobserved twisting of the near-infrared isophotes and the gas velocityfield. These are compatible with the presence of a global density wavedriven by the moderately strong stellar bar in this galaxy. We reviewrecent observational and modeling results on the circumnuclear region inM100, and discuss the implications for bar structure and gas dynamics inthe core of M100 and other disk galaxies.