Letter to the Editor

Mapping far-IR emission from the central kiloparsec of NGC 1097^*

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: sandstrom@mpia.de
² CEA/DSM/DAPNIA/Service d'Astrophysique, UMR AIM, CE Saclay, 91191 Gif sur Yvette Cedex, France
³ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁴ Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA
⁵ NASA Herschel Science Center, IPAC, California Institute of Technology, Pasadena, CA 91125, USA
⁶ Spitzer Science Center, California Institute of Technology, MC 314-6, Pasadena, CA 91125, USA
⁷ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
⁸ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁹ Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606, USA
¹⁰ Department of Physics & Astronomy, University of Wyoming, Laramie, WY 82071, USA
¹¹ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA

¹² Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
¹³ Departamento de Astrofisica, Facultad de Ciencias Fisicas, Universidad Complutense Madrid, Ciudad Universitaria, Madrid, 28040, Spain
¹⁴ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁵ Tianjin Astrophysics Center, Tianjin Normal University, Tianjin 300387, China
¹⁶ INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹⁷ Department of Physics and Astronomy, SUNY Stony Brook, Stony Brook, NY 11794-3800, USA
¹⁸ Hubble Fellow, National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
¹⁹ Institut d'Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98 bis Boulevard Arago, 75014 Paris, France
²⁰ ICRAR, M468, University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia
²¹ Department of Physics & Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada

Received: 30 March 2010
Accepted: 29 April 2010

Abstract

Using photometry of NGC 1097 from the Herschel PACS (Photodetector Array Camera and Spectrometer) instrument, we study the resolved properties of thermal dust continuum emission from a circumnuclear starburst ring with a radius ~900 pc. These observations are the first to resolve the structure of a circumnuclear ring at wavelengths that probe the peak (i.e. λ ~ 100 μm) of the dust spectral energy distribution. The ring dominates the far-infrared (far-IR) emission from the galaxy – the high angular resolution of PACS allows us to isolate the ring's contribution and we find it is responsible for 75, 60 and 55% of the total flux of NGC 1097 at 70, 100 and 160 μm, respectively. We compare the far-IR structure of the ring to what is seen at other wavelengths and identify a sequence of far-IR bright knots that correspond to those seen in radio and mid-IR images. The mid- and far-IR band ratios in the ring vary by less than ±20% azimuthally, indicating modest variation in the radiation field heating the dust on ~600 pc scales. We explore various explanations for the azimuthal uniformity in the far-IR colors of the ring including a lack of well-defined age gradients in the young stellar cluster population, a dominant contribution to the far-IR emission from dust heated by older (>10 Myr) stars and/or a quick smoothing of local enhancements in dust temperature due to the short orbital period of the ring. Finally, we improve previous limits on the far-IR flux from the inner ~600 pc of NGC 1097 by an order of magnitude, providing a better estimate of the total bolometric emission arising from the active galactic nucleus and its associated central starburst.