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HST Morphologies of z~2 Dust Obscured Galaxies II. Bump Sources
The Astrophysical Journal
  • R. S. Bussmann, University of Arizona
  • Arjun Day, National Optical Astronomy Observatory
  • J. Lotz, National Optical Astronomy Observatory
  • L. Armus, California Institute of Technology
  • M. J. Brown, Monash University
  • P. Eisenhardt, California Institute of Technology
  • James L. Higdon, Georgia Southern University
  • Sarah J.U. Higdon, Georgia Southern University
  • B. T. Januzzi, National Optical Astronomy Observatory
  • E. Le Floc'h, CEA-CNRS-Universite Paris Diderot
  • J. Melbourne, California Institute of Technology
  • B. T. Soifer, California Institute of Technology
  • D. Weedman, Cornell University
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We present Hubble Space Telescope imaging of 22 ultra-luminous infrared galaxies (ULIRGs) at z 2 with extremely red R – [24] colors (called dust-obscured galaxies, or DOGs) which have a local maximum in their spectral energy distribution (SED) at rest-frame 1.6 μm associated with stellar emission. These sources, which we call "bump DOGs," have star formation rates (SFRs) of 400-4000 M ☉ yr–1 and have redshifts derived from mid-IR spectra which show strong polycyclic aromatic hydrocarbon emission—a sign of vigorous ongoing star formation. Using a uniform morphological analysis, we look for quantifiable differences between bump DOGs, power-law DOGs (Spitzer-selected ULIRGs with mid-IR SEDs dominated by a power law and spectral features that are more typical of obscured active galactic nuclei than starbursts), submillimeter-selected galaxies, and other less-reddened ULIRGs from the Spitzer Extragalactic First Look Survey. Bump DOGs are larger than power-law DOGs (median Petrosian radius of 8.4 ± 2.7 kpc versus 5.5 ± 2.3 kpc) and exhibit more diffuse and irregular morphologies (median M 20 of –1.08 ± 0.05 versus –1.48 ± 0.05). These trends are qualitatively consistent with expectations from simulations of major mergers in which merging systems during the peak SFR period evolve from M 20 = –1.0 to M 20 = –1.7. Less-obscured ULIRGs (i.e., non-DOGs) tend to have more regular, centrally peaked, single-object morphologies rather than diffuse and irregular morphologies. This distinction in morphologies may imply that less-obscured ULIRGs sample the merger near the end of the peak SFR period. Alternatively, it may indicate that the intense star formation in these less-obscured ULIRGs is not the result of a recent major merger.


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Citation Information
R. S. Bussmann, Arjun Day, J. Lotz, L. Armus, et al.. "HST Morphologies of z~2 Dust Obscured Galaxies II. Bump Sources" The Astrophysical Journal Vol. 733 Iss. 1 (2011)
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