En ubrudt relation mellem impulsmoment og masse for skivegalakser

[BjarneModerator 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 (j_h∝M_h^2/3). 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.

 

[BjarneModerator 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 g_obs, the observed circular acceleration of the galaxy, and g_bar, the acceleration due to the total baryonic mass of the galaxy. For accelerations above 10^-10 m/s², g_obs traces g_bar, asymptoting to the 1:1 line. Below this scale, there is a break in the relation such that g_obs ∼ g_bar^1/2. 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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