Intrinsic shape of star-forming BzK galaxies. II. Rest-frame ultraviolet and optical structures in goods-south and SXDS

Abstract

We study the statistical intrinsic shape of star-forming BzK galaxies (sBzK galaxies) at z ∼ 2 in both rest-frame UV and rest-frame optical wavelengths. The sBzK galaxies are selected down to KAB = 24.0 mag in the GOODS-S and Subaru-XMM Deep Survey (SXDS) fields, where high-resolution images from the Hubble Space Telescope are publicly available. Of all 1028 galaxies in GOODS-S, 57% (583) show a single component in the Advanced Camera for Surveys/F850LP image. As Wide Field Camera (WFC3)/F160W images cover only part of GOODS-S and SXDS, 724/1028 and 2500/29835 sBzK galaxies in GOODS-S and SXDS, respectively, have WFC3 coverage. Of the sBzK galaxies in the WFC3/F160W images, 86% (626) and 82% (2044) appear as a single component in the GOODS-S and SXDS, respectively. A larger fraction of single-component objects in the F850LP images represents multiple star-forming regions in galaxies, while they are not so obvious in the F160W image which appears smoother. Most of the single-component sBzK galaxies show Sérsic indices of n = 0.5-2.5, in agreement with those of local disk galaxies. Their effective radii are 1.0-3.0 kpc and 1.5-4.0 kpc in F850LP and F160W images, respectively, regardless of the observed fields. The stellar surface mass density of the sBzK galaxies is also comparable to that of the local disk galaxies. However, the intrinsic shape of sBzK galaxies is not a round disk as seen in the local disk galaxies. By comparing apparent axial ratio (b/a) distributions of the sBzK galaxies with those of local disk galaxies by assuming tri-axial model with axes A > B > C, we found that their intrinsic face-on B/A ratios peak at B/A = 0.70 and B/A = 0.77-0.79 in the rest-frame UV and optical, respectively, and are statistically more bar-like than those of the local disk galaxies. The intrinsic edge-on C/A ratios in both rest-frame UV and optical wavelengths peak at 0.26, which is slightly larger than those of the local disk galaxies. Possible origins of this bar-like structure are bar instability, galaxy interaction, or continuous minor mergers. A study of galaxy structure evolution in cosmological simulations is desirable to examine the most likely scenario. © 2012. The American Astronomical Society. All rights reserved..