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Mid-Infrared IRS Spectroscopy of NGC 7331: A First Look at the SINGS Legacy

Authors
  • Jeffrey Smith
  • D, Dale
  • L, Armus
  • B, Draine
  • David Hollenbach
  • H. Roussel
  • G. Helou
  • R. C. Kennicutt, Jr.
  • A. Li
  • G. J. Bendo
  • D. Calzetti
  • C. W. Engelbracht
  • K. D. Gordon
  • T. H. Jarrett
  • L. Kewley
  • C. Leitherer
  • S. Malhotra
  • M. J. Meyer
  • E. J. Murphy
  • M. W. Regan
  • And 5 more
Type
Published Article
Journal
The Astrophysical Journal Supplement Series
Publisher
American Astronomical Society
Publication Date
Sep 01, 2004
Volume
154
Issue
1
Pages
154–154
Identifiers
DOI: 10.1086/423133
Source
SETI Institute
License
Green

Abstract

The nearby spiral galaxy NGC 7331 was spectrally mapped from 5 to 38 μm using all modules of Spitzer's Infrared Spectrograph (IRS). A strong new dust emission feature, presumed due to polycyclic aromatic hydrocarbons, was discovered at 17.1 μm. The feature's intensity is nearly half that of the ubiquitous 11.3 μm band. The 7-14 μm spectral maps revealed significant variation in the 7.7 and 11.3 μm PAH features between the stellar ring and nucleus. Weak [O IV] 25.9 μm line emission was found to be centrally concentrated in the nucleus, with an observed strength of over 10% of the combined neon line flux, indicating an AGN or unusually active massive star photoionization. Two [S III] lines fix the characteristic electron density in the H II regions at ne lesssim 200 cm-3. Three detected H2 rotational lines, tracing warm molecular gas, together with the observed IR continuum, are difficult to match with standard photodissociation region (PDR) models. Either additional PDR heating or shocks are required to simultaneously match lines and continuum.

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