2000/07/05 by Andreas Burkert, Burkert, Andreas
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics (astro-ph) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0007047
13 pages, 1 figure, submitted to ApJ Letters
arxiv created 2000/07/05 · openalex publication_date 2000/07/05 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The rotational properties of the visible and dark components of low-mass disk galaxies (vrot<=100 km/s) are investigated using the Swaters sample. The rotational parameter lambda'=lambdaDM*(jd/md) is determined, where lambdaDM is the dark halo spin parameter and jd/md is the ratio between the specific angular momentum of the disk and that of the dark halo. The distribution of lambda' is in excellent agreement with cosmological predictions of hierarchical clustering if jd/md=1, that is if the protogalactic gas did not loose a significant amount of specific angular momentum due to dynamical friction. This result is in disagreement with current cosmological Nbody/SPH simulations where the baryonic component looses 90% of its specific angular momentum while settling into the equatorial plane. The Swaters sample also shows a surprisingly strong correlation between lambda' and the baryonic mass fraction md: lambda'=0.4 md**0.6. This correlation can be explained if the total amount of gas in protogalaxies is a universal fraction of their dark matter mass, of order 10%, and if the variation in md is a result of the fact that only the inner parts of the primordial gas distribution managed to form a visible disk component. In this case the specific angular momentum of the gas out of which the disk formed is a factor of 2.75 larger than that of the dark halo, which would require a yet unknown spin-up process for the visible baryonic component.