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Galaxies 2014, 2(3), 292-299; doi:10.3390/galaxies2030292
Article

The Inner Regions of Disk Galaxies: A Constant Baryonic Fraction?

Received: 10 April 2014; in revised form: 18 June 2014 / Accepted: 19 June 2014 / Published: 10 July 2014
(This article belongs to the Special Issue Beyond Standard Gravity and Cosmology)
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Abstract: For 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.
Keywords: dark matter; galaxies: formation; galaxies; evolution dark matter; galaxies: formation; galaxies; evolution
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Lelli, F. The Inner Regions of Disk Galaxies: A Constant Baryonic Fraction? Galaxies 2014, 2, 292-299.

AMA Style

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.

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