We present very deep Wide Field Camera 3 ( WFC3 ) photometry of a massive , compact galaxy located in the Hubble Ultra Deep Field .
This quiescent galaxy has a spectroscopic redshift z = 1.91 and has been identified as an extremely compact galaxy by ( 7 ) .
We use new H _ { \mathrm { F 160 W } } imaging data obtained with Hubble Space Telescope/WFC3 to measure the deconvolved surface brightness profile to H \approx 28 mag arcsec ^ { -2 } .
We find that the surface brightness profile is well approximated by an n = 3.7 Sérsic profile .
Our deconvolved profile is constructed by a new technique which corrects the best-fit Sérsic profile with the residual of the fit to the observed image .
This allows for galaxy profiles which deviate from a Sérsic profile .
We determine the effective radius of this galaxy : r _ { e } = 0.42 \pm 0.14 kpc in the observed H _ { \mathrm { F 160 W } } -band .
We show that this result is robust to deviations from the Sérsic model used in the fit .
We test the sensitivity of our analysis to faint “ wings ” in the profile using simulated galaxy images consisting of a bright compact component and a faint extended component .
We find that due to the combination of the WFC3 imaging depth and our method ’ s sensitivity to extended faint emission we can accurately trace the intrinsic surface brightness profile , and that we can therefore confidently rule out the existence of a faint extended envelope around the observed galaxy down to our surface brightness limit .
These results confirm that the galaxy lies a factor \sim 10 off from the local mass-size relation .