En ubrudt relation mellem impulsmoment og masse for skivegalakser

Fora ASTRO-FORUM NYT FRA VIDENSKABEN En ubrudt relation mellem impulsmoment og masse for skivegalakser

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  • #317598

    Bjarne
    Moderator
    • Super Nova

    The angular momentum-mass relation: a fundamental law from dwarf irregulars to massive spirals

    In a ΛCDM Universe, the specific stellar angular momentum (j*) and stellar mass (M*) of a galaxy are correlated as a consequence of the scaling existing for dark matter haloes (jh∝Mh2/3). The shape of this law is crucial to test galaxy formation models, which are currently discrepant especially at the lowest masses, allowing to constrain fundamental parameters, e.g. the retained fraction of angular momentum. In this study, we accurately determine the empirical j*-M* relation (Fall relation) for 92 nearby spiral galaxies (from S0 to Irr) selected from the Spitzer Photometry and Accurate Rotation Curves (SPARC) sample in the unprecedented mass range 7 ≲ log M*/M ≲ 11.5. We significantly improve all previous estimates of the Fall relation by determining j* profiles homogeneously for all galaxies, using extended HI rotation curves, and selecting only galaxies for which a robust j* could be measured (converged j*(<R) radial profile). We find the relation to be well described by a single, unbroken power-law j*∝M*α over the entire mass range, with α=0.55±0.02 and orthogonal intrinsic scatter of 0.17±0.01 dex. We finally discuss some implications for galaxy formation models of this fundamental scaling law and, in particular, the fact that it excludes models in which discs of all masses retain the same fraction of the halo angular momentum.

    Denne ubrudte relation for skivegalakser over over et masseområde svarende til en faktor 100000 kan sandsynligvis forklare den tætte relation, som man finder mellem den radiale acceleration fra baryoner (stjerner) og den totale radiale acceleration fra baryoner og den mørke halo.

     

    #317599

    Bjarne
    Moderator
    • Super Nova

    The radial acceleration relation is a natural consequence of the baryonic Tully-Fisher relation

    Galaxies covering several orders of magnitude in stellar mass and a variety of Hubble types have been shown to follow the “Radial Acceleration Relation” (RAR), a relationship between gobs, the observed circular acceleration of the galaxy, and gbar, the acceleration due to the total baryonic mass of the galaxy. For accelerations above 10-10 m/s2, gobs traces gbar, asymptoting to the 1:1 line. Below this scale, there is a break in the relation such that gobs ∼ gbar1/2. We show that the RAR slope, scatter and the acceleration scale are all natural consequences of the well-known baryonic Tully-Fisher relation (BTFR). We further demonstrate that galaxies with a variety of baryonic and dark matter (DM) profiles and a wide range of dark halo and galaxy properties (well beyond those expected in CDM) lie on the RAR if we simply require that their rotation curves satisfy the BTFR. We explore conditions needed to break this degeneracy: sub-kpc resolved rotation curves inside of “cored” DM-dominated profiles and/or outside ≫ 100 kpc could lie on BTFR but deviate in the RAR, providing new constraints on DM.

     

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