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Where feedback fails: clues from the kinematics of disc galaxies
Lorenzo Posti (University of Strasbourg)
Thursday 23/01/2020 @ 11:30, Sala IV piano Battiferro
It is commonly believed that galaxies use, throughout the Hubble time, only a very small fraction of the baryons associated to their dark matter halos to form stars. The fact that galaxies have typically very low baryon-to-stars conversion efficiencies both at low-mass & high-mass is typically interpreted as a consequence of stellar & AGN feedback respectively. While this is robustly established for the average galaxy population, is this true for all galaxies? In this talk I will show that if we can measure accurately the kinematics of the cold gas in disc galaxies, which traces very well the circular velocity, then we can measure these baryon-to-stars conversion efficiencies quite reliably for individual objects. High-quality radio interferometric data can be used to collect a fairly large (>100) sample of nearby discs of all masses, from dwarfs to massive discs, from which we find a couple of surprises. 1) massive (>~10^11) spirals have systematically higher efficiencies than spheroids of similar masses and are in significant tension with “abundance matching” models; 2) isolated gas-rich ultra diffuse galaxies also have systematically higher efficiencies than a typical dwarf. These are two galaxy populations where AGN and stellar feedback, respectively, have failed to lower the baryon-to-stars conversion efficiencies. I will finally discuss the fundamental implications of these results on our understanding of feedback and of galaxy evolution.