Letter to the Editor

Far-infrared line imaging of the starburst ring in NGC 1097 with the Herschel/PACS spectrometer ^*

¹ Spitzer Science Center, California Institute of Technology, MC 314-6, Pasadena, CA 91125, USA e-mail: pedro@ipac.caltech.edu
² NASA Herschel Science Center, IPAC, California Institute of Technology, Pasadena, CA 91125, USA
³ Department of Physics and Astronomy, Mail Drop 111, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606, USA
⁴ Department of Physics & Astronomy, University of Wyoming, Laramie, WY 82071, USA
⁵ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁶ Department of Astronomy, University of Massachusetts, Amherst, MA 01003, 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 Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
¹⁰ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹¹ Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
¹² Departamento de Astrofisica, Facultad de Ciencias Fisicas, Universidad Complutense Madrid, Ciudad Universitaria, Madrid, 28040, Spain
¹³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁴ Tianjin Astrophysics Center, Tianjin Normal University, Tianjin 300387, PR China
¹⁵ INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹⁶ Department of Physics and Astronomy, SUNY Stony Brook, Stony Brook, NY 11794-3800, USA
¹⁷ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
¹⁸ Astrophysics Group, Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE; Kavli Institute for Cosmology, c/o Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹⁹ ICRAR, M468, University of Western Australia, 35 Stirling Hwy, Crawley, WA, 6009, Australia
²⁰ Institut d'Astrophysique de Paris, UMR7095 CNRS Université Pierre & Marie Curie, 98 bis boulevard Arago, 75014 Paris, France
²¹ CEA/DSM/DAPNIA/Service d'Astrophysique, UMR AIM, CE Saclay, 91191 Gif-sur-Yvette Cedex, France
²² Deptartment of Physics & Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada

Received: 30 March 2010
Accepted: 3 May 2010

Abstract

NGC 1097 is a nearby SBb galaxy with a Seyfert nucleus and a bright starburst ring. We study the physical properties of the interstellar medium (ISM) in the ring using spatially resolved far-infrared spectral maps of the circumnuclear starburst ring of NGC 1097, obtained with the PACS spectrometer on board the Herschel Space Observatory. In particular, we map the important ISM cooling and diagnostic emission lines of [OI] 63 μm, [OIII] 88 μm, [NII] 122 μm, [CII] 158 μm and [NII] 205 μm. We observe that in the [OI] 63 μm, [OIII] 88 μm, and [NII] 122 μm line maps, the emission is enhanced in clumps along the NE part of the ring. We observe evidence of rapid rotation in the circumnuclear ring, with a rotation velocity of ~220 km s^-1 (inclination uncorrected) measured in all lines. The [OI] 63 μm/[CII] 158 μm ratio varies smoothly throughout the central region, and is enhanced on the northeastern part of the ring, which may indicate a stronger radiation field. This enhancement coincides with peaks in the [OI] 63 μm and [OIII] 88 μm maps. Variations of the [NII] 122 μm/[NII] 205 μm ratio correspond to a range in the ionized gas density between 150 and 400 cm^-3.