Molecular gas in NUclei of GAlaxies (NUGA)^*,**

VII. NGC 4569, a large scale bar funnelling gas into the nuclear region

¹ LERMA, Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France e-mail: frederic.boone@obspm.fr
² Max-Planck-Institut für Radioastronomie, auf dem Hügel 69, 53121 Bonn, Germany
³ Department of Physics and Astronomy, Rutgers, the State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854, USA
⁴ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁵ Observatorio Astronómico Nacional (OAN) – Observatorio de Madrid, C/ Alfonso XII 3, 28014 Madrid, Spain
⁶ Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 St. Mt. d'Hères, France
⁷ INAF-Istituto di Radioastronomia/Sezione, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁸ IRAM Pico Veleta Observatory, Avenida Divina Pastora 7, Local 20, 18012 Granada, Spain
⁹ Harvard-Smithsonian Center for Astrophysics, SMA project, 645 N A`ohoku Pl., Hilo, HI 96720, USA
¹⁰ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
¹¹ Physikalisches Institut, Universität zu Köln, Zülpicherstrasse 77, 50937 Köln, Germany

Received: 7 February 2007
Accepted: 17 May 2007

Abstract

This work is part of the NUGA survey of CO emission in nearby active galaxies. We present observations of NGC 4569, a member of the Virgo Cluster. We analyse the molecular gas distribution and kinematics in the central region and we investigate a possible link to the strong starburst present at the nucleus. 70% of the [ 1.1±0.2] 10⁹  of molecular gas detected in the inner 20” is found to be concentrated within the inner 800 pc and is distributed along the large scale stellar bar seen in near-infrared observations. A hole in the CO distribution coincides with the nucleus where most of the Hα emission and blue light are emitted. The kinematics are modelled in three different ways, ranging from the purely geometrical to the most physical. This approach allows us to constrain progressively the physical properties of the galaxy and eventually to emerge with a reasonable fit to an analytical model of orbits in a barred potential. Fitting an axisymmetric model shows that the non-circular motions must be comparable in amplitude to the circular motions (120 km s^-1). Fitting a model based on elliptical orbits allows us to identify with confidence the single inner Lindblad resonance (ILR) of the large scale bar. Finally, a model based on analytical solutions for the gas particle orbits in a weakly barred potential constrained by the ILR radius reproduces the observations well. The mass inflow rate is then estimated and discussed based on the best fit model solution. The gravitational torques implied by this model are able to efficiently funnel the gas inside the ILR down to 300 pc, although another mechanism must take over to fuel the nuclear starburst inside 100 pc.