2026 Project Description

Finding Blue Clusters: When Did Galaxy Clusters Stop Forming Stars?

Supervisors

Tomomi Sunayama
Find out more about supervisors on ASIAA website

Task Description and Goals

Galaxy clusters are the largest gravitationally bound structures in the Universe and act as cosmic laboratories for studying how galaxies evolve. In the nearby Universe, most cluster galaxies are red and quenched—their star formation has been shut down after they fell into the dense cluster environment. But this was not always the case.

At earlier cosmic times, galaxy clusters were far more active. Many of their member galaxies were still blue, gas-rich, and forming stars. A key open question is:

When did galaxy clusters transition from being dominated by blue, star-forming galaxies to red, quenched ones?

In this project, the student will explore this transformation using state-of-the-art hydrodynamical cosmological simulations. By identifying galaxy clusters across cosmic time and measuring the fraction of blue versus red galaxies within them, the student will:

• Determine the redshift at which clusters become predominantly red
• Quantify how the blue fraction depends on redshift, cluster mass, and environment
• Compare results across multiple hydrodynamical simulations to assess robustness and physical drivers
• Gain hands-on experience with realistic simulated galaxy catalogs, data analysis, and visualization

This project connects directly to ongoing and upcoming surveys such as HSC, LSST, and Roman, and helps interpret observations of distant clusters by linking them to the underlying physical processes that shut down star formation.

Required Background

Strong programming skills, especially in Python