2006/01/31 by E. D'Onghia, Elena D’Onghia, Andreas Burkert +4
Physics and Astronomy · #Accretion (finance) #Angular momentum #Angular momentum coupling #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Classical mechanics #Cold dark matter #Context (archaeology) #Cosmology #Dark matter #Dark matter halo #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy formation and evolution #Galaxy merger #Halo #Physics #Radio Astronomy Observations and Technology #Redshift #Specific relative angular momentum #Total angular momentum quantum number #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2006.10996.x
published as Mon.Not.Roy.Astron.Soc.372:1525-1530,2006 · 7 pages, 5 figures, submitted to MNRAS. Request for high resolution figures to the authors
arxiv created 2006/01/31 · openalex publication_date 2006/10/11 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
The processes are investigated by which gas loses its angular momentum during the protogalactic collapse phase, leading to disc galaxies that are too compact with respect to the observations. High-resolution N-body/SPH simulations in a cosmological context are presented including cold gas and dark matter (DM). A halo with quiet merging activity since redshift z∼ 3.8 and with a high-spin parameter is analysed that should be an ideal candidate for the formation of an extended galactic disc. We show that the gas and the DM have similar specific angular momenta until a merger event occurs at z∼ 2 with a mass ratio of 5:1. All the gas involved in the merger loses a substantial fraction of its specific angular momentum due to tidal torques and dynamical friction processes falls quickly into the centre. In contrast, gas infall through small subclumps or accretion does not lead to catastrophic angular momentum loss. In fact, a new extended disc begins to form from gas that was not involved in the 5:1 merger event and that falls in subsequently. We argue that the angular momentum problem of disc galaxy formation is a merger problem: in cold dark matter cosmology substantial mergers with mass ratios of 1:1 to 6:1 are expected to occur in almost all galaxies. We suggest that energetic feedback processes could in principle solve this problem, however only if the heating occurs at the time or shortly before the last substantial merger event. Good candidates for such a coordinated feedback would be a merger-triggered starburst or central black hole heating. If a large fraction of the low angular momentum gas would be ejected, late-type galaxies could form with a dominant extended disc component, resulting from late infall, a small bulge-to-disc ratio and a low baryon fraction, in agreement with observations.