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The Inner Regions of Disk Galaxies: A Constant Baryonic Fraction?
AbstractFor disk galaxies (spirals and irregulars), the inner circular-velocity gradient dRV0 (inner steepness of the rotation curve) correlates with the central surface brightness ∑*,0 with a slope of ~0.5. This implies that the central dynamical mass density scales almost linearly with the central baryonic density. Here I show that this empirical relation is consistent with a simple model where the central baryonic fraction ƒbar,0 is fixed to 1 (no dark matter) and the observed scatter is due to differences in the baryonic mass-to-light ratio Mbar / LR (ranging from 1 to 3 in the R-band) and in the characteristic thickness of the central stellar component Δz (ranging from 100 to 500 pc). Models with lower baryonic fractions are possible, although they require some fine-tuning in the values of Mbar/LR and Δz. Regardless of the actual value of ƒbar,0, the fact that different types of galaxies do not show strong variations in ƒbar,0 is surprising, and may represent a challenge for models of galaxy formation in a Λ Cold Dark Matter (ΛCDM) cosmology.
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Lelli, F. The Inner Regions of Disk Galaxies: A Constant Baryonic Fraction? Galaxies 2014, 2, 292-299.View more citation formats
Lelli F. The Inner Regions of Disk Galaxies: A Constant Baryonic Fraction? Galaxies. 2014; 2(3):292-299.Chicago/Turabian Style
Lelli, Federico. 2014. "The Inner Regions of Disk Galaxies: A Constant Baryonic Fraction?" Galaxies 2, no. 3: 292-299.