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

September 2017 • 2017ApJ...846...32D

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

Abstract • 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 All-sky 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, Σ_IR. The median electron density of the ionized gas in LIRGs, based on the [N II]₁₂₂/[N II]₂₀₅ ratio, is n_e = 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]₁₅₈^PDR) = [C II]₁₅₈^PDR/[C II]₁₅₈, which increases from ∼60% to ∼95% in the warmest LIRGs. The [O I]₆₃/[C II]₁₅₈^PDR 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, n_H, and intensity of the interstellar radiation field, G, in units of G₀ and find G/n_H ratios of ∼0.1-50 G₀ cm³, with ULIRGs populating the upper end of the distribution. There is a relation between G/n_H and Σ _IR, showing a critical break at Σ_IR^* ≃ 5 × 10¹⁰ L_⊙ kpc^-2. Below Σ_IR^*, G/n_H remains constant, ≃0.32 G₀ cm³, and variations in Σ_IR are driven by the number density of star-forming regions within a galaxy, with no change in their PDR properties. Above Σ _IR^*, G/n_H increases rapidly with Σ_IR, 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.

Links

• PREPRINT http://arxiv.org/abs/1705.04326
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2017ApJ...846...32D
• ELECTR https://doi.org/10.3847%2F1538-4357%2Faa81d7
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2017ApJ...846...32D
• PDF https://iopscience.iop.org/article/10.3847/1538-4357/aa81d7/pdf
• PDF https://stacks.iop.org/0004-637X/846/32/pdf
• DATA http://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/846/32
• DATA http://archives.esac.esa.int/hsa/whsa/?ACTION=PUBLICATION&ID=2017ApJ...846...32D
• DATA https://irsa.ipac.caltech.edu/bibdata/2017/D/2017ApJ...846...32D.html