The Astrophysical Journal
We present Hubble Space Telescope imaging of 22 ultra-luminous infrared galaxies (ULIRGs) at z 2 with extremely red R –  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.
Bussmann, R. Shane, Arjun Day, Jennifer Lotz, Lee Armus, Michael J. I. Brown, Peter Eisenhardt, James L. Higdon, Sarah J.U. Higdon, Buell T. Januzzi, Emeric Le Floc'h, J. Melbourne, B. T. Soifer, Daniel Weedman.
"HST Morphologies of z~2 Dust Obscured Galaxies II. Bump Sources."
The Astrophysical Journal, 733 (1).
doi: 10.1088/0004-637X/733/1/21 source: http://arxiv.org/abs/1103.3527v1