HIGH-LYING OH ABSORPTION, [C II] DEFICITS, AND EXTREME LFIR/MH2 RATIOS IN GALAXIES
Journal article, 2015
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 mu m.3/2 J = 9/2-7/2 line (Weq(OH65)) with lower level energy Elow 300 K, is anticorrelated with the [Cii] 158 mu m line to far-infrared luminosity ratio, and correlated with the far-infrared luminosity per unit gas mass and with the 60-to-100 mu m far-infrared color. While all sources are in the active LIR/MH2 > 50L /M mode as derived from previous CO line studies, the OH65 absorption shows a bimodal distribution with a discontinuity at LFIR/MH2 100L /M . In the most buried sources, OH65 probes material partially responsible for the silicate 9.7 mu m absorption. Combined with observations of the OH 71 mu m.1/2 J = 7/2-5/2 doublet (Elow 415 K), radiative transfer models characterized by the equivalent dust temperature, Tdust, and the continuum optical depth at 100 mu m, t100, indicate that strong [C ii] 158 mu m deficits are associated with far-IR thick (t100 0.7, NH 1024 cm-2), warm (Tdust 60 K) structures where the OH 65 mu m absorption is produced, most likely in circumnuclear disks/tori/cocoons. With their high LFIR/MH2 ratios and columns, the presence of these structures is expected to give rise to strong [C ii] deficits. Weq(OH65) probes the fraction of infrared luminosity arising from these compact/warm environments, which is 30%-50% in sources with high Weq(OH65). Sources with high Weq(OH65) have surface densities of both LIR and MH2 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.
galaxies evolution
star-formation
Author
E. Gonzalez-Alfonso
University of Alcalá
J. Fischer
Naval Research Laboratory
E. Sturm
Max Planck Society
J. Gracia-Carpio
Max Planck Society
S. Veilleux
University of Maryland
M. Melendez
University of Maryland
D. Lutz
Max Planck Society
A. Poglitsch
Max Planck Society
Susanne Aalto
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
Niklas Falstad
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
H. W. W. Spoon
Cornell University
D. Farrah
Virginia Polytechnic Institute and State University
A. Blasco
University of Alcalá
C. Henkel
Max Planck Society
King Abdulaziz University
A. Contursi
Max Planck Society
A. Verma
University of Oxford
M. Spaans
University of Groningen
H. A. Smith
Harvard-Smithsonian Center for Astrophysics
M. L. N. Ashby
Harvard-Smithsonian Center for Astrophysics
S. Hailey-Dunsheath
California Institute of Technology (Caltech)
S. G. Burillo
Spanish National Observatory (OAN)
J. Martin-Pintado
Centro de Astrobiologia (CAB)
P. van der Werf
Leiden University
R. Meijerink
Leiden University
R. Genzel
Max Planck Society
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 800 1 1-10 69Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.1088/0004-637X/800/1/69