The Formation of the Most Massive Galaxies

Project Leader

The Brightest Cluster Galaxy (BCG) in the center of this cluster (Abell 2218) is surrounded by strongly lensed background galaxies (blue/red arcs) and a plethora of lower-mass cluster members. BCGs, which are the most massive in the Universe, lie at the centers of galaxy clusters and have a unique growth history that has contributions from cooling flows, gas-rich and gas-poor mergers, and accelerated early growth before the cluster formed. Credit: NASA, ESA, and Johan Richard (Caltech, USA)

In the centers of galaxy clusters, typically lives a single, massive galaxy surrounded by significantly-lower-mass neighbors. This massive galaxy is typically “red and dead”, with little ongoing star formation, suggesting that it has grown primarily via mergers with other quenched galaxies. In relaxed clusters, the position of this galaxy marks the gravitational potential minimum, with the central galaxy often surrounded by giant arcs indicating strong gravitational lensing. These central galaxies, known as “brightest cluster galaxies” (BCGs) are the most massive galaxies in the Universe, and represent an extreme channel of galaxy formation.

Using optical/infrared data from the Hubble Space Telescope and the Magellan telescopes in Chile, we are studying the assembly and evolution of these unique systems. The main questions that we are trying to answer are:

  • When did the BCG become a useful designation? When did these clusters become significantly more massive than their neighbors and separate from the rest of the pack?
  • Is there a meaningful connection between the assembly of the BCG and the growth of cool cores?
  • When did BCGs become radio loud? Is this related to when they settled into the center of the cluster?
  • How have BCGs grown so massive? At what epochs is this growth dominated by dry mergers, wet mergers, cooling flows, and in situ star formation?

Below are some relevant papers and links to ongoing collaborations/efforts.

Team Members