COSMOS2020: New Insights into Galaxy Assembly and Evolution over the first 10 Billion Years

The COSMOS field has proved to be one of the cornerstone surveys in extragalactic astronomy. We have built a new photometric redshift catalog COSMOS2020 from the latest ultra-deep imaging from Subaru, VISTA, and Spitzer. We measure 1M sources across the 2deg2 field using both apertures and profile-fitting photometry, pairing each with two SED fitting codes to derive four sets of precise photometric redshifts. We then measure the form and evolution the Galaxy Stellar Mass Function from 0.2 < z < 7.5 to reveal a strikingly constant rate of mass assembly stretching back into the Epoch of Reionization. We also find new samples of ultra-luminous galaxies at z>7.5 which form the most robust constraints on the UV Luminosity Function at such early times, confirming an excess of luminous sources. Are we witnessing a stage before feedback has suppressed their growth? Such a scenario challenges galaxy formation theory. We will have our answer soon; five of these luminous z~9 galaxies will be followed up with spatially resolved spectroscopy in the Cycle 1 JWST NIRSpec program BEASTS (PI:Weaver) where we will confirm this excess and reveal the mechanisms responsible for their fantastic growth.

John R. Weaver
John R. Weaver
PhD Fellow in Astrophysics

My research interests lie almost exclusively within the realm of extragalactic astrophysics and cosmology. I use state-of-the-art optical and infrared observatories and surveys to study the lives of galaxies, and how their properties change over cosmic time. This includes detailed case studies of individual galaxies, as well as statistical analyses of large survey catalogs.