The ATLAS3D project - XXVI. HI discs in real and simulated fast and slow rotators

Paolo Serra, Ludwig Oser, Davor Krajnovic, Thorsten Naab, Tom Oosterloo, Raffaella Morganti, Michele Cappellari, Eric Emsellem, Lisa M. Young, Leo Blitz, Timothy A. Davis, Pierre-Alain Duc, Michaela Hirschmann, Anne-Marie Weijmans, Katherine Alatalo, Estelle Bayet, Maxime Bois, Frederic Bournaud, Martin Bureau, Roger L. DaviesP. T. de Zeeuw, Sadegh Khochfar, Harald Kuntschner, Pierre-Yves Lablanche, Richard M. McDermid, Marc Sarzi, Nicholas Scott

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One quarter of all nearby early-type galaxies (ETGs) outside Virgo host a disc/ring of HI with size from a few to tens of kpc and mass up to ~ 1e+9 solar masses. Here we investigate whether this HI is related to the presence of a stellar disc within the host making use of the classification of ETGs in fast and slow rotators (FR/SR). We find a large diversity of HI masses and morphologies within both families. Surprisingly, SRs are detected as often, host as much HI and have a similar rate of HI discs/rings as FRs. Accretion of HI is therefore not always linked to the growth of an inner stellar disc. The weak relation between HI and stellar disc is confirmed by their frequent kinematical misalignment in FRs, including cases of polar and counter rotating gas. In SRs the HI is usually polar. This complex picture highlights a diversity of ETG formation histories which may be lost in the relative simplicity of their inner structure and emerges when studying their outer regions. We find that LCDM hydrodynamical simulations have difficulties reproducing the HI properties of ETGs. The gas discs formed in simulations are either too massive or too small depending on the star formation feedback implementation. Kinematical misalignments match the observations only qualitatively. The main point of conflict is that nearly all simulated FRs and a large fraction of all simulated SRs host corotating HI. This establishes the HI properties of ETGs as a novel challenge to simulations.
Original languageEnglish
Pages (from-to)3388-3407
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date17 Sept 2014
Publication statusPublished - 11 Nov 2014


  • ISM: kinematics and dynamics
  • Galaxies: elliptical and lenticular, cD
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: kinematics and dynamics


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