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

Journal Article · Fri Sep 01 04:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA81D7· OSTI ID:22875817

Díaz-Santos, T. ^[1]; Armus, L.; Howell, J. H. ^[2]; Charmandaris, V. ^[3]; Lu, N. ^[4]; Stierwalt, S.; Linden, S. T. ^[5]; Stacey, G. ^[6]; Malhotra, S. ^[7]; Werf, P. P. van der ^[8]; Privon, G. C. ^[9]; Mazzarella, J. M. ^[10]; Goldsmith, P. F. ^[11]; Murphy, E. J.; others, and

---

1. Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago (Chile)
2. Infrared Processing and Analysis Center, MC 314-6, Caltech, 1200 E. California Blvd., Pasadena, CA 91125 (United States)
3. Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, GR-15236, Penteli (Greece)
4. China-Chile Joint Center for Astronomy (CCJCA), Camino El Observatorio 1515, Las Condes, Santiago (Chile)
5. Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904 (United States)
6. Department of Astronomy, Cornell University, Ithaca, NY 14853 (United States)
7. Astrophysics Science Division, Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States)
8. Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden (Netherlands)
9. Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción (Chile)
10. Infrared Processing and Analysis Center, MC 100-22, Caltech, 1200 E. California Blvd., Pasadena, CA 91125 (United States)
11. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)

We present an analysis of [OI]{sub 63}, [O iii]{sub 88}, [N ii]{sub 122}, and [CII]{sub 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]{sub 122}, [OI]{sub 63}, and [CII]{sub 158} as a function of FIR color and infrared luminosity surface density, Σ{sub IR}. The median electron density of the ionized gas in LIRGs, based on the [N ii]{sub 122}/[N ii]{sub 205} ratio, is n{sub e} = 41 cm{sup −3}. We find that the dispersion in the [CII]{sub 158} deficit of LIRGs is attributed to a varying fractional contribution of photodissociation regions (PDRs) to the observed [CII]{sub 158} emission, f([C II]{sub 158}{sup PDR}) = [C II]{sub 158}{sup PDR}/[CII]{sub 158}, which increases from ∼60% to ∼95% in the warmest LIRGs. The [OI]{sub 63}/[C II]{sub 158}{sup PDR} ratio is tightly correlated with the PDR gas kinetic temperature in sources where [OI]{sub 63} is not optically thick or self-absorbed. For each galaxy, we derive the average PDR hydrogen density, n{sub H}, and intensity of the interstellar radiation field, G, in units of G{sub 0} and find G/n{sub H} ratios of ∼0.1–50 G{sub 0} cm{sup 3}, with ULIRGs populating the upper end of the distribution. There is a relation between G/n{sub H} and Σ{sub IR}, showing a critical break at Σ{sub IR}{sup ∗} ≃ 5 × 10{sup 10} L {sub ⊙} kpc{sup −2}. Below Σ{sub IR}{sup ∗}, G/n{sub H} remains constant, ≃0.32 G{sub 0} cm{sup 3}, and variations in Σ{sub IR} are driven by the number density of star-forming regions within a galaxy, with no change in their PDR properties. Above Σ{sub IR}{sup ∗}, G/n{sub H} increases rapidly with Σ{sub 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.

• OSTI ID: 22875817
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 846; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
DENSITY
DISPERSIONS
DISSOCIATION
DISTRIBUTION
ELECTRON DENSITY
EMISSION
FINE STRUCTURE
GALACTIC EVOLUTION
GALAXIES
GALAXY NUCLEI
HYDROGEN
LUMINOSITY
PHOTOLYSIS
STARS