The South Pole Telescope (SPT) has discovered a large sample of millimetre point sources in the 2500 deg^2 SPT-SZ survey. Follow-up observations with ALMA show that about 90% of these sources are strongly lensed dusty star-forming galaxies (DSFGs), while the remaining ~10% are compact groups of DSFGs at z~3-7, representing protocluster cores caught during their most intense phase of star formation. These systems are ideal laboratories for studying how intracluster gas first emerges and interacts with extreme star formation and AGN activity.
In this talk, I will introduce the SPT-selected protocluster sample and highlight our recent ALMA detection of hot intracluster gas at z=4.3 via the thermal Sunyaev–Zeldovich effect. I will discuss its implications and briefly outline future prospects for high-redshift ICM studies, including opportunities with the upcoming facilities such as ALMA Wideband Sensitivity Upgrade (WSU), ngVLA, Athena, and Lynx.
