Morphologies of high-redshift, dust-obscured galaxies from Keck laser guide star adaptive optics

Creators: Melbourne, J.; Desai, V.; Armus, Lee; Dey, Arjun; Brand, K.; Thompson, D.; Soifer, B. T.; Matthews, K.; Jannuzi, B. T.; Houck, J. R.

Abstract

Spitzer MIPS images in the Boötes field of the NOAO Deep Wide-Field Survey have revealed a class of extremely dust-obscured galaxy (DOG) at z ~ 2. The DOGs are defined by very red optical to mid-infrared (IR; observed-frame) colors, R – [24 μm] > 14 mag, i.e. f_ν(24 μm)/f_ν(R) > 1000. They are ultra-luminous infrared galaxies with L_(8-1000 μm) > 10^(12)-10^(14) L⊙, but typically have very faint optical (rest-frame UV) fluxes. We imaged three DOGs with the Keck laser guide star adaptive optics (LGSAO) system, obtaining ~0.06" resolution in the K'-band. One system was dominated by a point source, while the other two were clearly resolved. Of the resolved sources, one can be modeled as a exponential disk system. The other is consistent with a de Vaucouleurs profile typical of elliptical galaxies. The nonparametric measures of their concentration and asymmetry show the DOGs to be both compact and smooth. The AO images rule out double nuclei with separations of greater than 0.1" (<1 kpc at z = 2), making it unlikely that ongoing major mergers (mass ratios of 1/3 and greater) are triggering the high-IR luminosities. By contrast, high-resolution images of z ~ 2 SCUBA sources tend to show multiple components and a higher degree of asymmetry. We compare near-IR morphologies of the DOGs with a set of z = 1 luminous infrared galaxies (LIRGs; L_(IR) ~ 10^(11) L⊙) imaged with Keck LGSAO by the Center for Adaptive Optics Treasury Survey. The DOGs in our sample have significantly smaller effective radii, ~1/4 the size of the z = 1 LIRGs, and tend toward higher concentrations. The small sizes and high concentrations may help explain the globally obscured rest-frame blue-to-UV emission of the DOGs.

Additional Information

© 2008 The American Astronomical Society. Received 2007 December 11; accepted 2008 June 24; published 2008 August 6. The adaptive optics data presented herein were obtained at the Keck Observatory, which is operated as a scientific partnership among Caltech, UC, and NASA. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. The laser guide star adaptive optics system was funded by the W. M. Keck Foundation. The artificial laser guide star system was developed and integrated in a partnership between the Lawrence Livermore National Labs (LLNL) and the W. M. Keck Observatory. The laser was integrated at Keck with the help of Curtis Brown and Pamela Danforth. The NIRC2 near-IR camera was developed by Caltech and UCLA (P. I. Keith Matthews). This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. The project was funded in part by the Spitzer Science Center. We are especially grateful to the IRAC Shallow Survey team (P. I. Peter Eisenhardt) for providing observations in the Bootes field. We want to thank Dan Weedman, Steven Willner, and Daniel Stern for their helpful comments on the manuscript. We are grateful for the expert assistance of the staff of Kitt Peak National Observatory where the ground-based Bootes field observations of the NDWFS were obtained. The authors thank NOAO for supporting the NOAO Deep Wide-Field Survey. The research activities of A.D. and B.T.J. are supported by NOAO, which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation.

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