HIGH-LYING OH ABSORPTION, [C II] DEFICITS, AND EXTREME L {sub FIR}/M {sub H2} RATIOS IN GALAXIES
- Universidad de Alcalá, Departamento de Física y Matemáticas, Campus Universitario, E-28871 Alcalá de Henares, Madrid (Spain)
- Naval Research Laboratory, Remote Sensing Division, 4555 Overlook Avenue SW, Washington, DC 20375 (United States)
- Max-Planck-Institute for Extraterrestrial Physics (MPE), Giessenbachstraße 1, D-85748 Garching (Germany)
- Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
- Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-43992 Onsala (Sweden)
- Cornell University, Astronomy Department, Ithaca, NY 14853 (United States)
- Department of Physics, Virginia Tech, Blacksburg, VA 24061 (United States)
- Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121, Bonn (Germany)
- University of Oxford, Oxford Astrophysics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom)
- Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen (Netherlands)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
Herschel/PACS observations of 29 local (ultra)luminous infrared galaxies, including both starburst and active galactic nucleus (AGN) dominated sources as diagnosed in the mid-infrared/optical, show that the equivalent width of the absorbing OH 65 μm Π{sub 3/2} J = 9/2-7/2 line (W {sub eq}(OH65)) with lower level energy E {sub low} ≈ 300 K, is anticorrelated with the [C II]158 μm line to far-infrared luminosity ratio, and correlated with the far-infrared luminosity per unit gas mass and with the 60-to-100 μm far-infrared color. While all sources are in the active L {sub IR}/M {sub H2} > 50L {sub ☉}/M {sub ☉} mode as derived from previous CO line studies, the OH65 absorption shows a bimodal distribution with a discontinuity at L {sub FIR}/M {sub H2} ≈ 100 L {sub ☉}/M {sub ☉}. In the most buried sources, OH65 probes material partially responsible for the silicate 9.7 μm absorption. Combined with observations of the OH 71 μm Π{sub 1/2} J = 7/2-5/2 doublet (E {sub low} ≈ 415 K), radiative transfer models characterized by the equivalent dust temperature, T {sub dust}, and the continuum optical depth at 100 μm, τ{sub 100}, indicate that strong [C II]158 μm deficits are associated with far-IR thick (τ{sub 100} ≳ 0.7, N {sub H} ≳ 10{sup 24} cm{sup –2}), warm (T {sub dust} ≳ 60 K) structures where the OH 65 μm absorption is produced, most likely in circumnuclear disks/tori/cocoons. With their high L {sub FIR}/M {sub H2} ratios and columns, the presence of these structures is expected to give rise to strong [C II] deficits. W {sub eq}(OH65) probes the fraction of infrared luminosity arising from these compact/warm environments, which is ≳ 30%-50% in sources with high W {sub eq}(OH65). Sources with high W {sub eq}(OH65) have surface densities of both L {sub IR} and M {sub H2} higher than inferred from the half-light (CO or UV/optical) radius, tracing coherent structures that represent the most buried/active stage of (circum)nuclear starburst-AGN co-evolution.
- OSTI ID:
- 22364193
- Journal Information:
- Astrophysical Journal, Vol. 800, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Star formation rates from [C II] 158 μm and mid-infrared emission lines for starbursts and active galactic nuclei
FAR-INFRARED FINE-STRUCTURE LINE DIAGNOSTICS OF ULTRALUMINOUS INFRARED GALAXIES