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Published November 10, 2011 | Published
Journal Article Open

The Water Vapor Spectrum of APM 08279+5255: X-Ray Heating and Infrared Pumping over Hundreds of Parsecs


We present the rest-frame 200-320 μm spectrum of the z = 3.91 quasar APM 08279+5255, obtained with Z-Spec at the Caltech Submillimeter Observatory. In addition to the J = 8 → 7 to J = 13 → 12 CO rotational transitions which dominate the CO cooling, we find six transitions of water originating at energy levels ranging up to 643 K. Most are first detections at high redshift, and we have confirmed one transition with CARMA. The CO cooling is well described by our X-ray dominated region (XDR) model, assuming L_(1-100 keV) ~ 1 × 10^(46) erg s^(–1), and that the gas is distributed over a 550-pc size scale, as per the now-favored μ = 4 lensing model. The total observed cooling in water corresponds to 6.5 × 109 L_☉, comparable to that of CO. We compare the water spectrum with that of Mrk 231, finding that the intensity ratios among the high-lying lines are similar, but with a total luminosity scaled up by a factor of ~50. Using this scaling, we estimate an average water abundance relative to H_2 of 1.4 × 10^(–7), a good match to the prediction of the chemical network in the XDR model. As with Mrk 231, the high-lying water transitions are excited radiatively via absorption in the rest-frame far-infrared, and we show that the powerful dust continuum in APM 08279+5255 is more than sufficient to pump this massive reservoir of warm water vapor.

Additional Information

© 2011 American Astronomical Society. Received 2011 June 21; accepted 2011 July 13; published 2011 October 21. We are indebted to the staff of the Caltech Submillimeter Observatory for their help in Z-Spec's commissioning and observing. We acknowledge the following grants and fellowships: NASA SARA grants NAGS-11911 and NAGS-12788, NSF AST grant 0807990, an NSF Career grant (AST-0239270) and a Research Corporation Award (RI0928) to J. Glenn, a Caltech Millikan and JPL Director's fellowships to C.M.B., an NRAO Jansky fellowship to J. E. Aguirre, NASAGSRP fellowship to L. Earle, and an NSF GSRP award to J. Kamenetzky. The research described in this Letter, carried out at the Jet Propulsion Laboratory, California Institute of Technology, was done under a contract with the National Aeronautics and Space Administration.

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