Title: The Emergence of Galaxy Clusters - from Cosmic Dawn to Cosmic Noon

Speaker: Thomas Greve

Institute: Technical University of Denmark

Host: Siyi Feng

Time: 14:30-16:30, Thursday, April, 27

Location: Physics Building 552

Abstract:

Galaxy clusters are the most massive gravitationally-bound objects in the Universe. Their alluring beauty so prominently on display in the present-day Universe, mega-parsec-sized structures containing up to thousands of galaxies residing in massive dark matter halos, belies what is likely a complex and prolonged formation history. In this talk, I will present the results from a search of protocluster candidates at z > 6  (Cosmic Dawn) using the newly published COSMOS2020 catalogue, which contains new ultra-deep photometry in the optical/NIR bands of ∼ 106 sources over the full 2 square degree COSMOS area. We find several galaxy-rich and massive protocluster candidates at z > 6. They have dark matter halo masses, which are consistent with them ending up as Coma-like clusters in the present-day Universe. The abundance of massive z> 6 clusters challenges current models of hierarchical structure formation, which may indicate our incomplete understanding of the baryonic condensation at these early times. Using one of the Keck telescopes in Hawaii we have spectroscopically confirmed one of the z=6 protoclusters, and confirm that this is an extremely massive and rich structure. Combining our data with narrowband imaging and other spectroscopic data, we have found that this protocluster looks to be embedded in what could be a large-scale filament/structure at z=6. This is consistent with a picture in which protoclusters and galaxy overdensities reside at the nodes of large-scale filaments.

Bio：

I am an astronomer at the Cosmic Dawn Center in Copenhagen, Denmark.My work focuses on the formation and evolution of galaxies. I have a particular interest far-IR/mm observations with ALMA that can probe the physical conditions of the interstellar medium in high redshift galaxies. While my work mainly makes use of observations, I am also very interested in galaxy numerical simulations. I am also the Danish co-PI of the MIRI instrument onboard the James Webb Space Telescope,  where I am involved in the deep 5.6micron imaging survey of the Hubble Ultra Deep Field. With these unique data we are able to find some of the very first galaxies as they formed only a few hundred million years after the Big Bang.