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 2 deg$^2$ 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:John R. Weaver). I delve into the details of the PSF fitting and the cosmic variance analysis.

Christian Kragh Jespersen
Christian Kragh Jespersen
PhD Candidate in Astrophysical Sciences

My research interests are at the intersection between Machine Learning, galaxy formation and evolution, big surveys, and cosmology