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Published April 10, 2011 | Published
Journal Article Open

Constraints on the Assembly and Dynamics of Galaxies. I. Detailed Rest-frame Optical Morphologies on Kiloparsec Scale of z ~ 2 Star-forming Galaxies

Abstract

We present deep and high-resolution Hubble Space Telescope NIC2 F160W imaging at 1.6 μm of six z ~ 2 star-forming galaxies with existing near-infrared integral field spectroscopy from SINFONI at the Very Large Telescope. The unique combination of rest-frame optical imaging and nebular emission-line maps provides simultaneous insight into morphologies and dynamical properties. The overall rest-frame optical emission of the galaxies is characterized by shallow profiles in general (Sérsic index n < 1), with median effective radii of R_e ~ 5 kpc. The morphologies are significantly clumpy and irregular, which we quantify through a non-parametric morphological approach, estimating the Gini (G), multiplicity (Ψ), and M_(20) coefficients. The estimated strength of the rest-frame optical emission lines in the F160W bandpass indicates that the observed structure is not dominated by the morphology of line-emitting gas, and must reflect the underlying stellar mass distribution of the galaxies. The sizes and structural parameters in the rest-frame optical continuum and Hα emission reveal no significant differences, suggesting similar global distributions of the ongoing star formation and more evolved stellar population. While no strong correlations are observed between stellar population parameters and morphology within the NIC2/SINFONI sample itself, a consideration of the sample in the context of a broader range of z ~ 2 galaxy types (K-selected quiescent, active galactic nucleus, and star forming; 24 μm selected dusty, infrared-luminous) indicates that these galaxies probe the high specific star formation rate and low stellar mass surface density part of the massive z ~ 2 galaxy population, with correspondingly large effective radii, low Sérsic indices, low G, and high Ψ and M_(20). The combined NIC2 and SINFONI data set yields insights of unprecedented detail into the nature of mass accretion at high redshift.

Additional Information

© 2011 American Astronomical Society. Received 2010 November 5; accepted 2011 February 8; published 2011 March 24. We are grateful to M. Franx, L. Simard, A. Renzini, S. Wuyts, S. Genel, A. Sternberg, P. van Dokkum, and the entire SINS team for many stimulating discussions and insightful comments on various aspects of this work. We wish to thank in particular P. van Dokkum, L. Yan, and M. Kriek for kindly providing their reduced NIC2 images for the analysis, and N. Reddy for useful discussions on the IR properties of the sample. We thank S. Toft for advice on reducing NICMOS data and J. Greene for help with using GALFIT. We also thank the referee for a very constructive report and useful suggestions. N.M.F.S. acknowledges support by the Minerva program of the MPG. N.B. is supported by the Marie Curie grant PIOF-GA-2009-236012 from the European Commission. G.C. acknowledges support by the ASI-INAF grant I/009/10/0. Based on observations made with the NASA/ESA Hubble Space Telescope (HST), obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5−26555, and at the Very Large Telescope of the European Southern Observatory, Paranal, Chile (ESO Programme IDs 073.B-9018, 074.A-9011, 075.A-0466, 076.A-0527, 077.A-0576, 078.A-0600, 079.A-0341, 080.A-0330, and 080.A-0339).

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