Joint Astrophysics Colloquium

Probing the Accretion of Gas onto Galaxies:
Opportunities and Pitfalls

Claude-André Faucher-Giguère

UC Berkeley

Galaxies must continuously accrete gas from the intergalactic medium in order to sustain their observed star formation rates. How this accretion proceeds is a fundamental problem in galaxy formation, as it determines how rapidly galaxies can grow as a function of mass and redshift, as well as the efficiency of feedback processes. While theoretical work predicts that galaxies acquire most of their baryons via the “cold mode”, observations have so far not found clear traces of the cold streams. I will discuss results from a research program aimed at robustly quantifying the observational signatures of the cold mode, focusing on Ly-alpha emission and absorption and their connection to high-redshift “Ly-alpha blobs” and halo absorbers. In doing so, I will highlight some of the theoretical challenges involved, which can jeopardize this unique opportunity to test a physical prediction of galaxy formation if not addressed properly.