The mid-infrared high-ionization lines from active galactic nuclei and star-forming galaxies

Miguel Pereira-Santaella, Aleksandar M. Diamond-Stanic, Almudena Alonso-Herrero, George H. Rieke

Research output: Contribution to journalArticlepeer-review

82 Scopus citations


We used Spitzer/Infrared Spectrograph spectroscopic data on 426 galaxies including quasars, Seyferts, LINERs, and Hii galaxies to investigate the relationship among the mid-IR emission lines. There is a tight linear correlation between the [Ne v]14.3 μm and 24.3 μm (97.1 eV) and the [Oiv]25.9 μm (54.9 eV) high-ionization emission lines. The correlation also holds for these high-ionization emission lines and the [Ne iii]15.56 μm (41 eV) emission line, although only for active galaxies. We used these correlations to calculate the [Ne iii] excess due to star formation in Seyfert galaxies. We also estimated the [Oiv] luminosity due to star formation in active galaxies and determined that it dominates the [Oiv] emission only if the contribution of the active nucleus to the total luminosity is below 5%. We find that the active galactic nucleus dominates the [Oiv] emission in most Seyfert galaxies, whereas star formation adequately explains the observed [Oiv] emission in optically classified Hii galaxies. Finally, we computed photoionization models to determine the physical conditions of the narrow-line region where these high-ionization lines originate. The estimated ionization parameter range is -2.8 < log U < -2.5 and the total hydrogen column density range is 20 < log nH (cm-2) < 21.

Original languageEnglish (US)
Pages (from-to)2270-2280
Number of pages11
JournalAstrophysical Journal
Issue number2
StatePublished - Dec 20 2010


  • Galaxies: active
  • Galaxies: nuclei
  • Galaxies: starburst
  • Infrared: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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