  We present the first results from RomulusC, the highest resolution
cosmological hydrodynamic simulation of a galaxy cluster run to date. RomulusC,
a zoom-in simulation of a halo with $z=0$ mass $10^{14}$ M$_{\odot}$, is run
with the same sub-grid physics and resolution as Romulus25 (Tremmel et al.
2017). With unprecedented mass and spatial resolution, RomulusC represents a
unique opportunity to study the evolution of galaxies in dense environments
down to dwarf masses. We demonstrate that RomulusC results in an intracluster
medium (ICM) consistent with observations. The star formation history and
stellar mass of the brightest cluster galaxy (BCG) is consistent with
observations and abundance matching results, indicating that our sub-grid
models, optimized only to reproduce observations of field dwarf and Milky Way
mass galaxies, are able to produce reasonable galaxy masses and star formation
histories in much higher mass systems. Feedback from supermassive black holes
(SMBHs) regulates star formation by driving large-scale, collimated outflows
that coexist with a low entropy core. We find that non-BCG cluster member
galaxies are substantially quenched compared to the field down to dwarf galaxy
masses and, at low masses, quenching is seen to have no dependence on mass or
distance from the cluster center. This enhanced quenched population extends
beyond $R_{200}$ and is in place at high redshift. Similarly, we predict that
SMBH activity is significantly suppressed within clusters outside of the BCG,
but show how the effect could be lost when only focusing on the brightest AGN
in the most massive galaxies.
