Properties of Interstellar Medium In Infrared-Bright QSOs Probed by [O I] 63 μm and [C II] 158 μm Emission Lines

Creators: Zhao, Yinghe; Yan, Lin; Tsai, Chao-Wei

Abstract

We present a study of the interstellar medium (ISM) in the host galaxies of nine QSOs at 0.1 < z < 0.2 with black hole masses of 3 x 10^7 M_☉ to 3 x 10^9 M_☉ based on the far-IR spectroscopy taken with Herschel Space Observatory. We detect the [O I] 63 μm ([C II] 158 μm) emission in 6 (8) out of 8 (9) sources. Our QSO sample has far-infrared luminosities (L_(FIR) ~ several times 10^(11) L_☉. The observed line-to-L_(FIR) ratios (L_([O I])63μm/L_(FIR) and L_([C II])/L_(FIR) are in the ranges of 2.6 × 10^(−4) to 10^(−2) and 2.8 × 10^(−4) to 2 × 10^(−3), respectively (including upper limits). These ratios are comparable to the values found in local ULIRGs, but higher than the average value published so far for z > 1 IR-bright QSOs. One target, W0752+19, shows an additional broad velocity component (~720 km s^(−1)) and exceptionally strong [O I] 63 μm emission with L_([O I]63μm)/L_(FIR) of 10^(−2), an order of magnitude higher than the average value found among local (U)LIRGs. Combining with the analyses of the Sloan Digital Sky Survey optical spectra, we conclude that the [O I] 63 μm emission in these QSOs is unlikely excited by shocks. We infer that the broad [O I] 63 μm emission in W0752+19 could arise from the warm and dense ISM in the narrow-line region of the central active galactic nucleus. Another possible explanation is the existence of a dense gas outflow with n_H ~ 10^4 cm^(−3), where the corresponding broad [C II] emission is suppressed. Based on the far-IR [O I] and [C II] line ratios, we estimate constraints on the ISM density and UV radiation field intensity of n_H ≾ 10^(3.3) cm^(−3) and 10^3 < G_0 ≾ 10^(4.2), respectively. These values are consistent with those found in local Seyfert 1 ULIRGs. In contrast, the gas with broad velocity width in W0752+19 has n_H ≳ 10^(4.3) cm^(−3) and G_0 > 10^4.

Additional Information

© 2016 The American Astronomical Society. Received 2015 May 20; accepted 2016 March 23; published 2016 June 23. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. We thank the anonymous referee for her/his careful reading of the manuscript and the constructive comments/suggestions, which have helped to improve the paper. We also thank Dr. M. G. Wolfire for helpful discussion. Y.Z. is partially supported by the National Natural Science Foundation of China under grant nos. 11390373 and 11420101002, and the CAS pilot-b project #XDB09000000. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This paper also utilized the publicly available SDSS data sets. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the US Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Web site is http://www.sdss.org/. The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.

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