Gas discs in real and simulated early-type galaxies.

When viewed through their interstellar medium, early-type galaxies (E/S0s) constitute a surprisingly complex and diverse family -- to some extent much more intriguing than that of gas-rich spirals. I will discuss recent results obtained in this field as part of the Altas3D survey. About half of all early-type galaxies host between 1e+7 and many times 1e+9 M(sun) of atomic/molecular hydrogen gas, reaching up to ~10% of the stellar mass of the host. This gas is typically distributed on a disc with radius from a few kpc to many tens of kpc. How did these gas discs assemble? Observationally, the angular momentum misalignment between gas and stars may provide some hints. We find that gas and stars corotate in only ~half of the cases. In the remaining half the gas is distributed in a polar, counterrotating or warped configuration. This diversity may reflect the stochastic nature of gas accretion from satellites and from the intergalactic medium. Yet, LCDM hydrodynamical cosmological simulations -- which should incorporate such stochastic gas accretion -- do not reproduce the observed diversity of angular momentum misalignments. I will discuss recent and ongoing work in this area.


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