The Role of Black Hole Feedback on Size and Structural Evolution in
  Massive Galaxies
  We use cosmological hydrodynamical simulations to investigate the role of
feedback from accreting black holes on the evolution of sizes, compactness,
stellar core density and specific star-formation of massive galaxies with
stellar masses of $ M_{star} > 10^{10.9} M_{\odot}$. We perform two sets of
cosmological zoom-in simulations of 30 halos to z=0: (1) without black holes
and Active Galactic Nucleus (AGN) feedback and (2) with AGN feedback arising
from winds and X-ray radiation. We find that AGN feedback can alter the stellar
density distribution, reduce the core density within the central 1 kpc by 0.3
dex from z=1, and enhance the size growth of massive galaxies. We also find
that galaxies simulated with AGN feedback evolve along similar tracks to those
characterized by observations in specific star formation versus compactness. We
confirm that AGN feedback plays an important role in transforming galaxies from
blue compact galaxies into red extended galaxies in two ways: (1) it
effectively quenches the star formation, transforming blue compact galaxies
into compact quiescent galaxies and (2) it also removes and prevents new
accretion of cold gas, shutting down in-situ star formation and causing
subsequent mergers to be gas-poor or mixed. Gas poor minor mergers then build
up an extended stellar envelope. AGN feedback also puffs up the central region
through the fast AGN driven winds as well as the slow expulsion of gas while
the black hole is quiescent. Without AGN feedback, large amounts of gas
accumulate in the central region, triggering star formation and leading to
overly massive blue galaxies with dense stellar cores.
