Gravitational torques imply molecular gas inflow towards the nucleus of M 51

¹ Max Planck Institute for Astronomy, Königstuhl, 17, 69117 Heidelberg, Germany
e-mail: querejeta@mpia-hd.mpg.de
² Observatorio Astronómico Nacional, Alfonso XII, 3, 28014 Madrid, Spain
³ School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
⁴ Department of Physics, 4-181 CCIS, University of Alberta, Edmonton, AB T6G 2E1, Canada
⁵ Institut de Radioastronomie Millimétrique, 300 rue de la piscine, 38406 Saint-Martin d’Hères, France
⁶ CNRS, IRAP, 9 avenue Colonel Roche, BP 44346, 31028 Toulouse, France
⁷ Université de Toulouse, UPS-OMP, IRAP, 31028 Toulouse, France
⁸ Instituto Radioastronomía Milimétrica, Avda. Divina Pastora 7, Núcleo Central, 18012 Granada, Spain
⁹ Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
¹⁰ Observatoire de Paris, 61 avenue de l’Observatoire, 75014 Paris, France
¹¹ Center for Cosmology and AstroParticle Physics, The Ohio State University, 191 West Woodruff Avenue, Columbus, OH 43210, USA

Received: 10 October 2015
Accepted: 23 January 2016

Abstract

The transport of gas towards the centre of galaxies is critical for black hole feeding and, indirectly, it can control active galactic nucleus (AGN) feedback. We have quantified the molecular gas inflow in the central R< 1 kpc of M 51 to be 1 M_⊙/yr, using a new gravitational torque map and the molecular gas traced by the Plateau de Bure Interferometer Arcsecond Whirlpool Survey (PAWS). The nuclear stellar bar is responsible for this gas inflow. We also used torque profiles to estimate the location of dynamical resonances, and the results suggest a corotation for the bar CR_bar ~ 20′′, and a corotation for the spiral CR_sp ~ 100′′. We demonstrate how important it is to correct 3.6 μm images for dust emission when gravitational torques are to be computed, and we examine further sources of uncertainty. Our observational measurement of gas inflow can be compared with nuclear molecular outflow rates and provide useful constraints for numerical simulations.