The Inner Regions of Disk Galaxies: A Constant Baryonic Fraction?
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 baryoni...
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| Format: | Article |
| Language: | English |
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MDPI AG
2014-07-01
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| Series: | Galaxies |
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| Online Access: | http://www.mdpi.com/2075-4434/2/3/292 |
| _version_ | 1818446580230914048 |
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| author | Federico Lelli |
| author_facet | Federico Lelli |
| author_sort | Federico Lelli |
| collection | DOAJ |
| description | 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. |
| first_indexed | 2024-12-14T19:49:59Z |
| format | Article |
| id | doaj.art-2d63645ae703436fab3f100c9c7a0ef7 |
| institution | Directory Open Access Journal |
| issn | 2075-4434 |
| language | English |
| last_indexed | 2024-12-14T19:49:59Z |
| publishDate | 2014-07-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Galaxies |
| spelling | doaj.art-2d63645ae703436fab3f100c9c7a0ef72022-12-21T22:49:26ZengMDPI AGGalaxies2075-44342014-07-012329229910.3390/galaxies2030292galaxies2030292The Inner Regions of Disk Galaxies: A Constant Baryonic Fraction?Federico Lelli0Department of Astronomy, Case Western Reserve University, 10090 Euclid Ave, Cleveland, OH 44106, USAFor 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.http://www.mdpi.com/2075-4434/2/3/292dark mattergalaxies: formationgalaxiesevolution |
| spellingShingle | Federico Lelli The Inner Regions of Disk Galaxies: A Constant Baryonic Fraction? Galaxies dark matter galaxies: formation galaxies evolution |
| title | The Inner Regions of Disk Galaxies: A Constant Baryonic Fraction? |
| title_full | The Inner Regions of Disk Galaxies: A Constant Baryonic Fraction? |
| title_fullStr | The Inner Regions of Disk Galaxies: A Constant Baryonic Fraction? |
| title_full_unstemmed | The Inner Regions of Disk Galaxies: A Constant Baryonic Fraction? |
| title_short | The Inner Regions of Disk Galaxies: A Constant Baryonic Fraction? |
| title_sort | inner regions of disk galaxies a constant baryonic fraction |
| topic | dark matter galaxies: formation galaxies evolution |
| url | http://www.mdpi.com/2075-4434/2/3/292 |
| work_keys_str_mv | AT federicolelli theinnerregionsofdiskgalaxiesaconstantbaryonicfraction AT federicolelli innerregionsofdiskgalaxiesaconstantbaryonicfraction |