High-redshift elliptical galaxies: are they (all) really compact?

We investigate the properties of 12 ultramassive passively evolving early-type galaxies (ETGs) at z(phot) > 1.4 in the COSMOS 2 deg2 field. These 12 ETGs were selected as pBzKs, have accurate 1.4 less than or similar to z(phot) less than or similar to 1.7, high Sersic index profiles typical of ellipticals, no detection at 24 mu m, resulting in a complete ETG sample at M* > 2.5 x 1011 M(circle dot) (Chabrier initial mass function). Contrary to the previous claims, the half-light radii estimated in very high signal-to-noise ratio imaging data from Hubble Space Telescope+Advanced Camera for Surveys (ACS) are found to be large for most of the sample, consistent with local ellipticals. If the high-redshift ETGs with M* < 2.5 x 1011 M(circle dot) are really small in size and compact as reported in the previous studies, our result may suggest a 'downsizing' scenario, whereby the most massive ETGs reach their final structure earlier and faster than the lower mass ones. However, simulating galaxies with morphological properties fixed to those of local ETGs with the same stellar mass show that the few compact galaxies that we still recover in our sample can be understood in terms of fluctuations due to noise preventing the recovery of the extended low surface brightness haloes in the light profile. Such haloes, typical of Sersic profiles, extending even up to 40 kpc, are indeed seen in our sample.