Hubble space telescope morphologies of z ~ 2 dust-obscured galaxies. II. Bump sources

R S Bussman, Arjun Dey, J Lotz, Lee Armus, Michael Brown, V Desai, P Eisenhardt, Jim Higdon, Sarah Higdon, Buell Jannuzi, E Le Floc'h, Jason Melbourne, B Soifer, Dan Weedman

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    25 Citations (Scopus)

    Abstract

    We present Hubble Space Telescope imaging of 22 ultra-luminous infrared galaxies (ULIRGs) at z a?? 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 I?m associated with stellar emission. These sources, which we call bump DOGs, have star formation rates (SFRs) of 400-4000 MaS? 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 A? 2.7 kpc versus 5.5 A? 2.3 kpc) and exhibit more diffuse and irregular morphologies (median M 20 of -1.08 A? 0.05 versus -1.48 A? 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.
    Original languageEnglish
    Pages (from-to)1 - 18
    Number of pages18
    JournalThe Astrophysical Journal
    Volume733
    Issue number1
    DOIs
    Publication statusPublished - 2011

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