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Mid-infrared Properties of OH Megamaser Host Galaxies. II. Analysis and Modeling of the Maser Environment

Willett, Kyle W. and Darling, Jeremy and Spoon, Henrik W. W. and Charmandaris, Vassilis and Armus, Lee (2011) Mid-infrared Properties of OH Megamaser Host Galaxies. II. Analysis and Modeling of the Maser Environment. Astrophysical Journal, 730 (1). Art. No. 56. ISSN 0004-637X.

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We present a comparison of Spitzer Infrared Spectrograph (IRS) data for 51 OH megamaser (OHM) hosts and 15 non-masing ultraluminous infrared galaxies (ULIRGs). 10%-25% of the OHMs show evidence for the presence of an active galactic nucleus (AGN), significantly lower than the estimated AGN fraction from previous optical and radio studies. Non-masing ULIRGs have a higher AGN fraction (50%-95%) than OHMs, although some galaxies in both samples show evidence of co-existing starbursts and AGNs. Radiative transfer models of the dust environment reveal that non-masing galaxies tend to have clumpy dust geometries commonly associated with AGN, while OHMs have deeper absorption consistent with a smooth, thick dust shell. Statistical analyses show that the major differences between masing and non-masing ULIRGs in the mid-IR relate to the optical depth and dust temperature, which we measure using the 9.7 μm silicate depth and 30-20 μm spectral slope from the IRS data. Dust temperatures of 40-80 K derived from the IRS data are consistent with predictions of OH pumping models and with a minimum T_(dust) required for maser production. The best-fit dust opacities (τ_V ~ 100-400), however, are nearly an order of magnitude larger than those predicted for OH inversion, and suggest that modifications to the model may be required. These diagnostics offer the first detailed test of an OHM pumping model based only on the properties of its host galaxy and provide important restrictions on the physical conditions relevant to OHM production.

Item Type:Article
Related URLs:
URLURL TypeDescription
Willett, Kyle W.0000-0002-3654-3504
Darling, Jeremy0000-0003-2511-2060
Spoon, Henrik W. W.0000-0002-8712-369X
Charmandaris, Vassilis0000-0002-2688-1956
Armus, Lee0000-0003-3498-2973
Additional Information:© 2011 American Astronomical Society. Received 2010 March 19; accepted 2011 January 26; published 2011 March 3. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory (JPL) and the California Institute of Technology, under NASA contract 1407. Additional observations were also taken at the Arecibo Observatory (NAIC/Cornell). We made extensive use of the NASA/IPAC Extragalactic Database (NED) which is operated by JPL and Caltech under contract with NASA. Many thanks are due to J. Stocke for jump-starting work with Spitzer, D. Dale for discussions about mid-IR line ratios, P. Lockett and M. Elitzur for sharing their radiative transfer models, and the Spitzer Science Center for hosting K.W. and J.D. while collaborating on data analysis. V.C. acknowledges partial support from the EU ToK grant 39965 and FP7-REGPOT 206469.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
European Research Council (ERC)39965
European Research Council (ERC)206469
Subject Keywords:dust, extinction – galaxies: active – galaxies: starburst – infrared: galaxies – masers – radio lines: galaxies
Issue or Number:1
Classification Code:PACS: 98.54.Cm, 98.62.Ve, 98.58.Bz, 98.62.Bj
Record Number:CaltechAUTHORS:20110419-104109356
Persistent URL:
Official Citation:Kyle W. Willett et al. 2011 ApJ 730 56 doi: 10.1088/0004-637X/730/1/56
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:23379
Deposited By: Benjamin Perez
Deposited On:19 Apr 2011 18:17
Last Modified:05 Nov 2019 06:12

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