A Herschel/PACS Far-infrared Line Emission Survey of Local Luminous Infrared Galaxies

T. Díaz-Santos, L. Armus, V. Charmandaris, N. Lu, S. Stierwalt, G. Stacey, S. Malhotra, P. P.Van Der Werf, J. H. Howell, G. C. Privon, J. M. Mazzarella, P. F. Goldsmith, E. J. Murphy, L. Barcos-Muñoz, S. T. Linden, H. Inami, K. L. Larson, A. S. Evans, P. Appleton, K. IwasawaS. Lord, D. B. Sanders, J. A. Surace

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168 Scopus citations


We present an analysis of [O I]63, [O III]88, [N II]122, and [C II]158 far-infrared (FIR) fine-structure line observations obtained with Herschel/PACS, for ∼240 local luminous infrared galaxies (LIRGs) in the Great Observatories Allsky LIRG Survey. We find pronounced declines ("deficits") of line-to-FIR continuum emission for [N II]122, [O I]63, and [C II]158 as a function of FIR color and infrared luminosity surface density, IR. The median electron density of the ionized gas in LIRGs, based on the [N II]122/[N II]205 ratio, is ne=41 cm-3. We find that the dispersion in the [C II]158 deficit of LIRGs is attributed to a varying fractional contribution of photodissociation regions (PDRs) to the observed [C II]158 emission, f ([C II]158PDR)=[C II]158PDR/[C II]158, which increases from ∼60% to ∼95% in the warmest LIRGs. The [O I]63/[C II]158PDR ratio is tightly correlated with the PDR gas kinetic temperature in sources where [O I]63 is not optically thick or self-absorbed. For each galaxy, we derive the average PDR hydrogen density, nH, and intensity of the interstellar radiation field, G, in units of G0 and find G/nH ratios of ∼0.1-50G0cm3, with ULIRGs populating the upper end of the distribution. There is a relation between G/nH and IR, showing a critical break at IR∗; 5 × 1010 L kpc-2. BelowIR∗, G/nH remains constant, ;0.32G0cm3, and variations inIR are driven by the number density of star-forming regions within a galaxy, with no change in their PDR properties. AboveIR∗, G/nH increases rapidly withIR, signaling a departure from the typical PDR conditions found in normal star-forming galaxies toward more intense/harder radiation fields and compact geometries typical of starbursting sources.

Original languageEnglish (US)
Article number32
JournalAstrophysical Journal
Issue number1
StatePublished - Sep 1 2017


  • galaxies: ISM
  • galaxies: evolution
  • galaxies: nuclei
  • galaxies: starburst
  • infrared: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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