Structure of Protocluster Galaxies: Accelerated Structural Evolution in   Overdense Environments?
  We present a high spatial-resolution HST/NICMOS imaging survey in the field of a known protocluster surrounding the powerful radio galaxy MRC1138-262 at z=2.16. Previously, we have shown that this field exhibits a substantial surface overdensity of red J-H galaxies. Here we focus on the stellar masses and galaxy effective radii in an effort to compare and contrast the properties of likely protocluster galaxies with their field counterparts and to look for correlations between galaxy structure and (projected) distance relative to the radio galaxy.   We find a hint that quiescent, cluster galaxies are on average less dense than quiescent field galaxies of similar stellar mass and redshift. In fact, we find only two (of nine) quiescent protocluster galaxies are of simliar density to the majority of the massive, quiescent compact galaxies (SEEDs) found in several field surveys. Furthermore, there is some indication that the structural Sersic n parameter is higher (n ~ 3-4) on average for cluster galaxies compared to the field SEEDs (n ~ 1-2) This result may imply that the accelerated galaxy evolution expected (and observed) in overdense regions also extends to structural evolution presuming that massive galaxies began as dense (low n) SEEDs and have already evolved to be more in line with local galaxies of the same stellar mass. 
A.W. Zirm, S. Toft, M. Tanaka
astro-ph.CO