An HST/WFC3-IR Morphological Survey of Galaxies at z = 1.5-3.6. I. Survey Description and Morphological Properties of Star-forming Galaxies

Creators: Law, David R.; Steidel, Charles C.; Shapley, Alice E.; Nagy, Sarah R.; Reddy, Naveen A.; Erb, Dawn K.

Abstract

We present the results of a 42-orbit Hubble Space Telescope Wide-Field Camera 3 (HST/WFC3) survey of the rest-frame optical morphologies of star-forming galaxies with spectroscopic redshifts in the range z = 1.5-3.6. The survey consists of 42 orbits of F160W imaging covering ~65 arcmin2 distributed widely across the sky and reaching a depth of 27.9 AB for a 5σ detection within a 0.2 arcsec radius aperture. Focusing on an optically selected sample of 306 star-forming galaxies with stellar masses in the range M_* = 10^9-10^(11) M_☉, we find that typical circularized effective half-light radii range from ~0.7 to 3.0 kpc and describe a stellar mass-radius relation as early as z ~ 3. While these galaxies are best described by an exponential surface brightness profile (Sérsic index n ~ 1), their distribution of axis ratios is strongly inconsistent with a population of inclined exponential disks and is better reproduced by triaxial stellar systems with minor/major and intermediate/major axis ratios ~0.3 and 0.7, respectively. While rest-UV and rest-optical morphologies are generally similar for a subset of galaxies with HST/Advanced Camera for Surveys imaging data, differences are more pronounced at higher masses M_* > 3 × 10^(10) M_☉. Finally, we discuss galaxy morphology in the context of efforts to constrain the merger fraction, finding that morphologically identified mergers/non-mergers generally have insignificant differences in terms of physical observables such as stellar mass and star formation rate, although merger-like galaxies selected according to some criteria have statistically smaller effective radii and correspondingly larger Σ_(SFR).

Additional Information

© 2012 American Astronomical Society. Received 2011 July 15; accepted 2011 December 4; published 2012 January 3. Based in part on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation. D.R.L., C.C.S., and S.R.N. have been supported by grant GO-11694 from the Space Telescope Science Institute. Support for D.R.L. and N.A.R. was also provided by NASA through Hubble Fellowship grants HF-51244.01 and HF-01223.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. C.C.S. has been supported by the US National Science Foundation through grants AST-0606912 and AST-0908805. A.E.S. acknowledges support from the David and Lucile Packard Foundation. D.R.L. appreciates productive conversations with A. Dutton and E. Bell, and thanks the referee (J. Lotz) for insightful comments that improved the final version of the manuscript. Finally, we extend thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests.

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