THE MORPHOLOGY OF PASSIVELY EVOLVING GALAXIES AT z ∼ 2 FROM HUBBLE SPACE TELESCOPE/WFC3 DEEP IMAGING IN THE HUBBLE ULTRA DEEP FIELD

We present near-IR images, obtained with the Hubble Space Telescope and the WFC3/IR camera, of six passive and massive galaxies at redshift 1.3 < z < 2.4 (specific star formation rate <10−2 Gyr−1; stellar mass M ∼ 1011 M☉), selected from the Great Observatories Origins Deep Survey. These images, which have a spatial resolution of ∼1.5 kpc, provide the deepest view of the optical rest-frame morphology of such systems to date. We find that the light profile of these galaxies is regular and well described by a Sérsic model with index typical of today's spheroids. Their size, however, is generally much smaller than today's early types of similar stellar masses, with four out of six galaxies having re ∼ 1 kpc or less, in quantitative agreement with previous similar measures made at rest-frame UV wavelengths. The images reach limiting surface brightness μ∼ 26.5 mag arcsec−2 in the F160W bandpass; yet, there is no evidence of a faint halo in the galaxies of our sample, even in their stacked image. We also find that these galaxies have very weak “morphological k-correction” between the rest-frame UV (from the Advanced Camera for Surveys z band) and the rest-frame optical (WFC3 H band): the Sérsic index, physical size, and overall morphology are independent or only mildly dependent on the wavelength, within the errors.