"Angular Momentum Acquisition in Milky Way Sized Galaxy Halos"

 

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ABSTRACT:

Using high-resolution cosmological hydrodynamic simulations, we study the angular momentum acquisition of Milky Way sized galaxies, as well as the gaseous halos surrounding them. We find that "cold flow" gas accretion (gas that never shock-heats as it falls onto galaxies from the cosmic web) enters galaxy halos with roughly 70% more angular momentum than dark matter, when averaged over cosmic time. In fact, we find that all matter has more specific angular momentum when measured at first accretion, rather than averaged over the galaxy's lifetime. Combined with the fact that cold flow gas spends a relatively short time in the galaxy halo (1-2 dynamical times) before sinking to the center, this naturally explains why it has a higher spin parameter than the dark matter halo, and often forms extended "cold flow disks" of material that extend far beyond the visible portion of the galaxy. We demonstrate that the higher angular momentum associated with cold flow gas is related to the fat that it tends to be preferentially accreted along cosmic filaments.