Explaining two circumnuclear star forming rings in NGC 5248^⋆

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: vanderlaan@iram.fr
² Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 St. Martin d’Hères, Grenoble, France
³ European Southern Observatory, Karl-Schwarzschild-Str 2, 85748 Garching, Germany
⁴ European Space Agency, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands
⁵ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁶ CSIRO Astronomy and Space Science, ATNF, PO Box 76, Epping NSW 1710, Australia
⁷ Astrophysics Research Institute, Liverpool John Moores University, Birkenhead CH41 1LD, UK
⁸ Observatoire Astronomique de Strasbourg, CNRS UMR 7550, 67000 Strasbourg, France

Received: 26 March 2013
Accepted: 17 June 2013

Abstract

The distribution of gas in the central kiloparsec of a galaxy has a dynamically rapid evolution. Nonaxisymmetries in the gravitational potential of the galactic disk, such as a large scale stellar bar or spiral, can lead to significant radial motion of gaseous material from larger radii to the central region. The large influx of gas and the subsequent star formation keep the central region constantly changing. However, the ability of gas to reach the nucleus proper to fuel an AGN phase is not guaranteed. Gas inflow can be halted at a circumnuclear star forming ring several hundred parsec away. The nearby galaxy NGC 5248 is especially interesting in this sense since it is said to host 2 circumnuclear star forming rings at 100 pc and 370 pc from its quiescent nucleus. Here we present new subarcsecond PdBI+30 m CO(2−1) emission line observations of the central region. For the first time the molecular gas distribution at the smallest stellar ring is resolved into a gas ring, consistent with the presence of a quiescent nucleus. However, the molecular gas shows no ring structure at the larger ring. We combine analyses of the gaseous and stellar content in the central kiloparsec of this galaxy to understand the gas distribution and dynamics of this star forming central region. We discuss the probability of two scenarios leading to the current observations, given our full understanding of this system, and discuss whether there are really two circumnuclear star forming rings in this galaxy.