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RomulusC: Galaxy Evolution in Dense Environments

How is galaxy evolution different in dense environments like groups and clusters?


Galaxy clusters and groups are unique places to study galaxy evolution because of their high density and the fact that, in their centers, they host the most massive galaxies in the Universe. Understanding how star formation is regulated in the central galaxies and how the intercluster medium (ICM) affects the evolution of other member galaxies are important areas of current research. The RomulusC simulation, the highest resolution cosmological simulation of a galaxy cluster run to date, will allow us to understand the evolution of galaxies in dense environments in more detail than ever before. It is the first of several simulations we are running focused on studying the most massive structures in the Universe at unprecedented resolution. I am analyzing these simulations in collaboration with many individuals, including Tom Quinn (U of Washington), Iryna Butsky (U of Washington), Arif Babul (U of Victoria), Priyamvada Natarajan (Yale), Angelo Ricarte (Yale), Daisuke Nagai (Yale), Urmila Chadayammuri (Yale), Ferah Munshi (Oklahoma), Alyson Brooks (Rutgers), and Anna Wright (Rutgers).

romulusC stars romulusC gas den romulusC gas temp
The Highest Resolution Galaxy Cluster Simulation. The distribution of stars (top, uvj colors; red = older stars, blue = younger), gas column density (middle; pink = high density, blue/green = low density), and gas temperature (weighted by density2; black = cold, yellow = hot). The snapshot is the cluster as it looks at z = 0.5 (t ~ 8.6 billion years since the Big Bang, or ~ 5 billion years ago).

A Predictive Model for Galaxy Evolution in Clusters

RomulusC is run with the same resolution and physics as the Romulus25 simulation. The physics of the simulation have been optimized to reproduce observations of galaxies ranging from dwarf to Milky Way masses. There has been no attempt to calibrate the simulation to produce realistic galaxy clusters. Further, the model for AGN feedback that I have implemented does not assume anything about the nature of large-scale outflows driven by the SMBH. In other words, the properties of cluster galaxies, the nature of AGN outflows, and the internal structure of the cluster are purely predictions of the simulation.

AGN Feedback and the Evolution of the Brightest Cluster Galaxy

Central brightest cluster galaxies are the most massive galaxies in the Universe. In RomulusC, we find that large-scale, columnated outflows driven by the central AGN is able to successfully regulate star formation in the BCG. I am using RomulusC to study how AGN feedback interacts with the ICM on large scales and how this interaction regulates cooling and star formation in the BCG. This work is being done in collaboration with In collaboration with Tom Quinn (U of Washington), Arif Babul (U of Victoria), Daisuke Nagai (Yale), and Urmila Chadayammuri (Yale)

Extreme Outflows in the Most Massive Galaxies. A map of temperature and velocity centered on the central galaxy of the RomulusC cluster. Large-scale, powerful outflows can be seen. They are driven by energy from a SMBH in the center of the galaxy. These outflows make it so that gas in the center of the cluster cannot cool as efficiently, thereby limiting star formation in the central galaxy.

Studying Cluster Galaxies

The unprecedented resolution of RomulusC, and the fact that our sub-grid models produce a broadly realistic inter-cluster medium (ICM), means that we can study galaxy evolution in dense environments with more detail than ever before. With Angelo Ricarte (Yale) and Priyamvada Natarajan (Yale), we are looking at the role of ram pressure stripping in quenching star formation as well as driving (and eventually hindering) black hole growth in cluster galaxies. In collaboration with Anna Wright (Rutgers), Alyson Brooks (Rutgers), Ferah Munshi (Oklahoma), and Daisuke Nagai (Yale) I am examining the evolution and structure of dwarf galaxies in both the field (Romulus25) and cluster environments (RomulusC).

environment quenching
Quenching Star Formation in Dense Environments. The fraction of cluster galaxies in RomulusC (blue) that are quenched at present day compared with the fraction of isolated galaxies taken from Romulus25 (orange). Other data are observations for isolated galaxies (black points, line) and those in cluster environments (grey). Low mass galaxies in clusters, which RomulusC can resolve better than any other simulation, are nearly all non-star forming regardless of their mass. This is in stark contrast to isolated dwarf galaxies which are almost never quenched.

More Simulations to Come

In collaboration with Tom Quinn (U of Washington), I am expanding the RomulusC series to include more groups and clusters of mass 2x1013 to 1015 Msun. More on this to come!

© 2018 Michael Tremmel | Based on the template design by Andreas Viklund