Skip to main content
Article
IRS Spectra of Two Ultraluminous Infrared Galaxies at z = 1.3
The Astrophysical Journal (2006)
  • V. Desai, California Institute of Technology
  • L. Armus, California Institute of Technology
  • B. T. Soifer, California Institute of Technology
  • D. W. Weedman, Cornell University
  • Sarah J.U. Higdon, Cornell University
  • C. Bian, California Institute of Technology
  • C. Borys, California Institute of Technology
  • H. W. W. Spoon, Cornell University
  • V. Charmandaris, Cornell University
  • K. Brand, National Optical Astronomy Observatory
  • M. J. I. Brown, Princeton University
  • A. Dey, National Optical Astronomy Observatory
  • J. L. Higdon, Cornell University
  • J. R. Houck, Cornell University
  • B. T. Jannuzi, National Optical Astronomy Observatory
  • E. Le Floc'h, University of Arizona
  • M.L.N. Ashby, Harvard-Smithsonian Center for Astrophysics
  • H. A. Smith, Harvard-Smithsonian Center for Astrophysics
Abstract
We present low-resolution (64 < R < 124) mid-infrared (8–38 m) spectra of two z  1:3 ultraluminous infrared galaxies (ULIRGs) with L8 1000 m  1013 L. The spectra were taken with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. Both objects were discovered in the NOAO Deep Wide-Field Survey (NDWFS) Bootes field. MIPS J142824.0+352619 is a bright 160 m source with a large infrared-to-optical flux density ratio. Previous authors provided evidence for a foreground lens and estimated an amplification of P10, although this factor is currently poorly constrained. The 6.2, 7.7, 11.3, and 12.8 m polycyclic aromatic hydrocarbon (PAH) emission bands in its IRS spectrum indicate a redshift of z  1:3. The large equivalent width of the 6.2 m PAH feature indicates that at least 50% of the mid-infrared energy is generated in a starburst, an interpretation supported by a large ½Ne ii/½Ne iii ratio and a low upper limit on the X-ray luminosity. SST24 J142827.19+354127.71 has the brightest 24 m flux (10.55 mJy) among optically faint (R > 20) galaxies in the NDWFS. Its mid-infrared spectrum lacks emission features, but the broad 9.7 m silicate absorption band places this source at z  1:3. Optical spectroscopy confirms a redshift of z ¼ 1:293  0:001. Given this redshift, SST24 J142827.19+354127.71 has among the largest rest-frame 5 m luminosities known. The similarity of its SED to those of known AGN-dominated ULIRGs and its lack of either PAH features or large amounts of cool dust indicate that the mid-infrared emission is dominated by an AGN rather than a starburst. 
Keywords
  • Galaxies,
  • Active,
  • Evolution,
  • Formation,
  • Starburst,
  • Infrared
Publication Date
April 10, 2006
DOI
10.1086/500426
Publisher Statement
This version of the paper was obtained from arXIV.org. In order for the work to be deposited in arXIV.org, the author must have copyright or it must be available under the Creative Commons Attribution license,Creative Commons Attribution-Noncommercial-ShareAlike license, orCreate Commons Public Domain Declaration. The publisher's final edited version of this article will be available at The Astrophysical Journal.
Citation Information
V. Desai, L. Armus, B. T. Soifer, D. W. Weedman, et al.. "IRS Spectra of Two Ultraluminous Infrared Galaxies at z = 1.3" The Astrophysical Journal Vol. 641 Iss. 1 (2006) p. 133 - 139
Available at: http://works.bepress.com/sarah_higdon/12/