colloquium – Shuowen Jin: Massive galaxies and clusters in the making: Multi-wavelength study of optically-dark SMGs and galaxy overdensities at z>2.5

Recent studies have revealed an important population of submillimeter galaxies (SMGs) that dropped out in deep optical surveys, however their nature is still largely unknown. On the other hand, high-z protoclusters are often suspected to be forming the local massive clusters, while the evolutionary path is still elusive. Thus discovering more SMGs and galaxy overdensities towards high redshift are key to pushing our understanding of the formation of massive galaxies and structures. Here I report recent discoveries and study on the two topics from our team, including (1) spectroscopic confirmation of a sample of optically-dark SMGs at z~4–6 using ALMA, NOEMA and JWST; (2) detailed insight into a z=2.58 HST-dark SMG by synergy of JWST and ALMA data; (3) discovery of protoclusters and compact galaxy groups at z~3–5 using NOEMA, ALMA and JWST. We found that most of the optically-dark SMGs have optically thick dust in FIR, and they consist of s significant fraction of star-forming galaxies at z~4. By comparison with simulations, we revealed that low-mass and compact galaxy groups most likely merge into single massive galaxies at lower-z, i.e., “proto-massive galaxy”, while only the most massive protoclusters are likely to evolve to local clusters.