We investigate a large sample of ~700 spectroscopic members down to 10^8.5 Msol in the CLASH cluster MACS1206 at z=0.45 from the highest-density core to the cluster's infall regions. We look for different cluster-specific effects by splitting the phase-space into 3 bins, disentangling environmental effects from stellar mass, main driver for field galaxies. To ensure reliable size measurements we exploit the capabilities of the multi-band fitting routine Galapagos2 from the MegaMorph team that fits Sersic profiles to galaxies and bulge/disk components in the Subaru Suprimecam BVRIz filters simultaneously. Dividing our sample into discrete morphological types as well as based on their star-formation activity, we follow distinct paths: We find a decrease in sizes of disk-like SF galaxies at same stellar masses by up to 20% (increasing in denser regions) in comparison to field survey measurements of similar kind. For early type quiescent galaxies this change is not significant.
The reported trends appear to be mainly driven by the fractional increase of bulge-dominated systems. By decomposing the galaxies, we can explain the smaller sizes of disk galaxies in clusters with their gradual replacement by bulge-dominated early-type disks (with the same mass distribution). Here, the size evolution and related environmental quenching seem to be dominated by the environmentally induced bulge growth that concentrates mass at smaller radii and fades the disk. For high-mass spheroidals, dry mergers and halo-related quenching drive the mass and size growth proportionally - along the mass-size sequence - leading to no measurable size differences in clusters and field.