Mid-infrared spectroscopy of infrared-luminous galaxies with subarcsecond resolution

B. T. Soifer, G. Neugebauer, K. Matthews, E. Egami, A. J. Weinberger

Research output: Contribution to journalArticlepeer-review

41 Scopus citations

Abstract

Low spectral resolution (Δλ/λ ∼ 50) mid-infrared observations with high angular resolution (0″.3-0″.5) using the Long Wavelength Spectrometer on the Keck I Telescope are reported of the nuclei of five highly luminous infrared-bright galaxies. Spectra of eight distinct nuclei, ranging in luminosity from ≤1011 to more than 10 12 L have been obtained. Four of the nuclei show the characteristic polycyclic aromatic hydrocarbon (PAH) emission features, i.e., 11.3 μm emission, as well as the 8.6 μm shoulder of the 7.7 μm band. The other nuclei show either weak PAH emission bands or no evidence for these bands. The high spatial resolution of the observations reveals extended emission in the 11.3 μn PAH band associated with several of the compact nuclear sources. When proper account is taken of the diffuse PAH emission, most of the compact sources show little or no directly associated PAH emission. The diffuse PAH emission is extended over spatial scales of 100-500 pc; its presence shows that there is significant circumnuclear UV-optical emission exciting the aromatic bands, most likely associated with circumnuclear starbursts. After the spectra of the nuclear sources are corrected for the spectrum of the diffuse PAH emission, the peak apparent silicate optical depth at 9.7 μm can be as large as 15, corresponding to more than 150 mag of visible light extinction. Because of the large silicate optical depths, mid-infrared spectra are not probing the nature of the true nuclei in the most opaque compact sources.

Original languageEnglish (US)
Pages (from-to)2980-2989
Number of pages10
JournalAstronomical Journal
Volume124
Issue number5 1763
DOIs
StatePublished - Nov 2002
Externally publishedYes

Keywords

  • Galaxies: individual (Arp 220, IRAS 08572+3915, Markarian 273, Markarian 463, W 114)
  • Infrared radiation
  • Techniques: spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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