The circumgalactic medium: where baryons collide

22-26 jun. 2020
Institut d'AStrophysique de Paris (IAP) 98 bis bd Arago 75014 PARIS - Paris (Francia)
The circum-galactic medium (CGM) surrounding galaxies is the interface between gas accreting from the cosmic web and outflows driven by massive stars and active galactic nuclei (AGN) in galaxies. It is the processes that occur as baryons flow into and out of the CGM that undoubtedly regulates galaxy formation and evolution. The CGM, and by extension to the most massive halos, the inter-cluster medium, are significant reservoirs of gas, metals, and dust, likely as significant as the total baryon content within galaxies. Over the last 3 decades, observers have identified 3 significant problems in the physical characteristics of galaxies which are still largely with us at present. These mysteries are (1) why is galaxy formation so inefficient? Despite the universe containing about 17% baryons, galaxies only have a fraction of this total. Galaxies have a maximum of only ~20% of the universal baryon fraction. Where are these “missing baryons”?; (2) The integrated total star formation as a function of redshift produces more metals than can be accounted for within galaxies at any redshift. Where are these “missing metals”?; and (3) galaxies across cosmic time do not appear to be able to sustain their star formation until the present time. Where does the gas come from the sustains the star formation that we have observed during the current age of the Universe? This 36th IAP colloquium will set the baseline for our understanding of the CGM at the dawn of the JWST era. Moreover, as the CGM will be an important component in justifying future facilities such as Athena, such a meeting will provide directions for the capabilities of these missions. We are now at a cross-roads: as more and more data are taken and simulations are becoming more sophisticated, it is time to take stock of what we know and how we can make progress in answering the above questions raised by our new understanding of the CGM.
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