Astron. Astrophys. 333, 864-876 (1998)

Molecular gas in the barred spiral M 100

II. ¹² CO(1-0) interferometer observations and numerical simulations

S. García-Burillo ¹, M.J. Sempere ¹, F. Combes ² and R. Neri <sup>3

1</sup> Observatorio Astronómico Nacional, Campus Universitario, Apdo 1143, E-28800 Alcalá de Henares (Madrid), Spain
² Observatoire de Paris, DEMIRM, 61 Av. de l'Observatoire, France
³ IRAM, 300 Rue de la Piscine, France

Received 27 October 1997 / Accepted 27 January 1998

Abstract

Using the IRAM interferometer we have mapped at high resolution () the ¹² CO(1-0) emission in the nucleus of the doubled barred SABbc spiral M 100. Our synthesized map includes the zero spacing flux of the single-dish 30m map (Sempere & García-Burillo, 1997, Paper I). Molecular gas is distributed in a two spiral arm structure starting from the end points of the nuclear bar ( pc) up to kpc, and a central source ( 100 pc). The kinematics of the gas indicates the existence of a steep rotation curve ( =180 km s^-1 at pc) and strong streaming motions characteristic of a trailing spiral wave inside corotation. Interpretation of the CO observations and their relation with stellar and gaseous tracers (K, optical, H , H I and radiocontinuum maps) are made in the light of a numerical model of the clouds hydrodynamics. Gas flow simulations analyse the gas response to a gravitational potential derived from the R and K-band plates, 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 kms^-1 kpc^-1) for the nuclear bar (with corotation at =1.2 kpc) decoupled from the slow pattern of the outer bar+spiral ( =23 kms^-1 kpc^-1) (with corotation at =8-9 kpc). As required by non-linear coupling of spirals (Tagger et al 1987), the corotation of the fast pattern falls in the ILR region of the slow pattern, allowing an efficient transfer of molecular gas towards the nuclear region. Solutions based on a single pattern hypothesis for the whole disk cannot fit the observed molecular gas response and fail to account for the relation between other stellar and gaseous tracers. In the two-bar solution, the gas morphology and kinematics are strongly varying in the rotating frame of the slow large-scale bar, and fit the data periodically during a short fraction (about 20%) of the relative nuclear bar period of 46 Myr.

Key words: galaxies: kinematics and dynamics galaxies: ISM galaxies: spiral galaxies: individual: M 100 radio lines: galaxies

Send offprint requests to: S. García-Burillo

© European Southern Observatory (ESO) 1998

Online publication: April 28, 1998

helpdesk@link.springer.de