Adaptive Optics Rest-Frame V-Band Imaging of Lyman Break Galaxies at z~3: High Surface Density Disklike Galaxies?

Abstract

In order to reveal the rest-frame V-band morphology of galaxies at z ~ 3, we conducted AO-assisted K-band imaging observations of z ~ 3 LBGs whose absolute magnitudes range from M_V* - 0.5 mag to M_V* + 3.0 mag, with M_V*, the characteristic absolute magnitude of z ~ 3 LBGs, of -24.0 mag. The AO observations resolve most LBGs at a resolution of FWHM ~ 0.2''. The median apparent half-light radius, r_HL, is 0.23'', i.e., 1.8 kpc at z = 3. LBGs brighter than M_V* have larger r_HL (0.40'') than the fainter LBGs (0.23^'') on average, and there are no bright LBGs with a small r_HL. LBGs brighter than M_V* have red rest-frame U - V colors (average of 0.2 mag), and most of the fainter LBGs show blue rest-frame U - V colors (average of -0.4 mag). The K-band peaks of some of the LBGs brighter than K = 22.0 mag show a significant shift from those in the optical images. We fit a Sérsic profile to the images of the LBGs with K < 21.5 mag, taking care of the uncertainty of the final PSFs at the position of the targets. The images of all but one LBG with K < 21.5 mag are fitted well with Sérsic profiles with n indexes less than 2, similar to disk galaxies in the local universe. For the fainter LBGs, we examine the concentration parameter instead of fitting a Sérsic profile; the concentration parameters of the LBGs are consistent with those of disk galaxies. Assuming that the LBGs have a disk shape, we compared their size-luminosity and size-stellar mass relations with those of z = 0 and z = 1 disk galaxies. The LBGs are brighter than z = 0 and z = 1 disk galaxies at the same effective radius. The rest-frame V-band surface brightness of the LBGs are 2.2-2.9 mag and 1.2-1.9 mag brighter than the disk galaxies at z = 0 and z = 1, respectively. The size-stellar mass relation of the LBGs shows that the effective radii of the LBGs do not depend on their stellar mass. For LBGs brighter than M_V*, the average surface stellar mass density is 3-6 times larger than those of the z = 0 and z = 1 disk galaxies. On the contrary, the size-stellar mass relation of the less-luminous LBGs is similar to those of z = 0 and z = 1 disk galaxies. We also examine the profiles of the serendipitously observed DRGs. They are fitted with Sérsic profiles with n < 2, and their scatter on the C versus r_HL plane is similar to that of the z ~ 3 LBGs. The average surface stellar mass density of the DRGs is even larger than that of the z ~ 3 LBGs brighter than M_V*. The implications of the dominance of the n < 2 population among galaxies at z ~ 3 and the presence of the high surface stellar mass density disk systems are discussed.

Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.