Large Disklike Galaxies at High Redshift

Abstract

Using deep near-infrared imaging of the Hubble Deep Field-South with the Infrared Spectrometer and Array Camera on the Very Large Telescope, we find six large disklike galaxies at redshifts z = 1.4-3.0. The galaxies, selected in Ks (2.2 μm), are regular and surprisingly large in the near-infrared (rest-frame optical), with face-on effective radii re = 065-09 or 5.0-7.5 h kpc in a Λ cold dark matter cosmology, comparable to the Milky Way. The surface brightness profiles are consistent with an exponential law over 2-3 effective radii. The Wide Field Planetary Camera 2 morphologies in Hubble Space Telescope imaging (rest-frame UV) are irregular and show complex aggregates of star-forming regions ~2'' (~15 h kpc) across, symmetrically distributed around the Ks-band centers. The spectral energy distributions show clear breaks in the rest-frame optical. The breaks are strongest in the central regions of the galaxies and can be identified as the age-sensitive Balmer/4000 A break. The most straightforward interpretation is that these galaxies are large disk galaxies; deep near-infrared data are indispensable for this classification. The candidate disks constitute 50% of galaxies with LV 6 × 1010 h L☉ at z = 1.4-3.0. This discovery was not expected on the basis of previously studied samples. In particular, the Hubble Deep Field-North is deficient in large galaxies with the morphologies and profiles we report here.