We take advantage of the Hubble Ultra Deep Field ( UDF ) data to study the restframe optical and ultra violet ( UV ) morphologies of the novel population of Distant Red Galaxies ( DRGs ) .
Six galaxies with J - K _ { s } > 2.3 are found to K _ { s } = 21.5 , five of which have photometric redshifts z _ { phot } \gtrsim 2 , corresponding to a surface density of 0.9 arcmin ^ { -2 } .
The surface brightness distributions of the z _ { phot } \gtrsim 2 galaxies are better represented by exponential disks than R ^ { 1 / 4 } -laws .
Two of the z _ { phot } \gtrsim 2 galaxies are extended , while three have compact morphologies .
The restframe optical morphology of the z _ { phot } \gtrsim 2 galaxies is quite different from the restframe UV morphology : all the galaxies have red central components which dominate in the NICMOS H _ { 160 } -band images , and distinct off-center blue features which show up in ( and often dominate ) the ACS images .
The mean measured effective radius of the z _ { phot } \gtrsim 2 galaxies is \langle r _ { e } \rangle = 1.9 \pm 1.4 kpc , similar ( within the errors ) to the mean size of LBGs at similar redshifts .
All the DRGs are resolved in the ACS images , while four are resolved in the NICMOS images .
Two of the z _ { phot } \gtrsim 2 galaxies are bright X-ray sources and hence host AGN .
One of these galaxies is resolved in the ACS and NICMOS images , which means the AGN does not dominate its restframe UV-optical SED , while the other is unresolved in the NICMOS images and hence could have an AGN dominated SED .
The diverse restframe optical and UV morphological properties of DRGs derived here suggest that they have complex stellar populations , consisting of both evolved populations that dominate the mass and the restframe optical light , and younger populations , which show up as patches of star formation in the restframe UV light ; in many ways resembling the properties of normal local galaxies .
This interpretation is supported by fits to the broadband SEDs , which for all five z _ { phot } \gtrsim 2 are best represented by models with extended star formation histories and substantial amounts of dust .