Desai, Vandana and Soifer, B. T. and Dey, Arjun and Le Floc'h, Emeric and Armus, Lee and Brand, Kate and Brown, Michael J. I. and Brodwin, Mark and Jannuzi, Buell T. and Houck, James R. and Weedman, Daniel W. and Ashby, Matthew L. N. and Gonzalez, Anthony and Huang, Jiasheng and Smith, Howard A. and Teplitz, Harry and Willner, Steve P. and Melbourne, Jason (2009) Strong polycyclic aromatic hydrocarbon emission from z ≈ 2 ULIRGs. Astrophysical Journal, 700 (2). pp. 1190-1204. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20090812-121204500
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Using the Infrared Spectrograph on board the Spitzer Space Telescope, we present low-resolution (64 < λ/δλ < 124), mid-infrared (20-38 μm) spectra of 23 high-redshift ULIRGs detected in the Boötes field of the NOAO Deep Wide-Field Survey. All of the sources were selected to have (1) f_ν(24 μm)>0.5 mJy; (2) R – >14 Vega mag; and (3) a prominent rest frame 1.6 μm stellar photospheric feature redshifted into Spitzer's 3-8 μm IRAC bands. Of these, 20 show emission from polycyclic aromatic hydrocarbons (PAHs), usually interpreted as signatures of star formation. The PAH features indicate redshifts in the range 1.5 < z < 3.0, with a mean of <z> = 1.96 and a dispersion of 0.30. Based on local templates, these sources have extremely large infrared luminosities, comparable to that of submillimeter galaxies. Our results confirm previous indications that the rest-frame 1.6 μm stellar bump can be efficiently used to select highly obscured star-forming galaxies at z ≈ 2, and that the fraction of starburst-dominated ULIRGs increases to faint 24 μm flux densities. Using local templates, we find that the observed narrow redshift distribution is due to the fact that the 24 μm detectability of PAH-rich sources peaks sharply at z = 1.9. We can analogously use observed spectral energy distributions to explain the broader redshift distribution of Spitzer-detected ULIRGs that are dominated by an active galactic nucleus (AGN). Finally, we conclude that z ≈ 2 sources with a detectable 1.6 μm stellar opacity feature lack sufficient AGN emission to veil the 7.7 μm PAH band.
|Additional Information:||© 2009 American Astronomical Society. Print publication: Issue 2 (2009 August 1); received 2009 January 9; accepted for publication 2009 May 27 Published 2009 July 10. Based on observations made with the Spitzer Space Telescope, operated by the Jet Propulsion Laboratory under NASA contract 1407. We thank the anonymous referee for suggestions that improved this paper. Support for M.B. was provided by the W.M. Keck Foundation. A.H.G. acknowledges support from a National Science Foundation (NSF) Small Grant for Exploratory Research under award AST-0436681. This work made use of images and data products provided by the NOAO Deep Wide-Field Survey (Jannuzi & Dey 1999), which is supported by the National Optical Astronomy Observatory (NOAO). NOAO is operated by AURA, Inc., under a cooperative agreement with the NSF. The Spitzer MIPS and IRAC surveys of the Boötes region were obtained using GTO time provided by the Spitzer Infrared Spectrograph Team (PI: James Houck), M. Rieke, and the IRAC Team (PI: G. Fazio). IRAC is supported in part through contract 960541 issued by JPL. The IRS was a collaborative venture between Cornell University and Ball Aerospace Corporation funded by NASA through the Jet Propulsion Laboratory and the Ames Research Center. Support for this work by the IRS GTO team at Cornell University was provided by NASA through contract 1257184 issued by JPL/Caltech. Facilities: Spitzer (MIPS, IRAC, IRS), Mayall (Mosaic-1), KPNO:2.1m (ONIS, SQUID, FLAMINGOS, FLAMINGOS-1)|
|Subject Keywords:||galaxies: active; galaxies: evolution; galaxies: formation; galaxies: starburst; infrared: galaxies|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||13 Aug 2009 19:32|
|Last Modified:||26 Dec 2012 11:11|
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