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The Origin of Dwarf Galaxies, Cold Dark Matter, and Biased Galaxy Formation: 1986

The Origin of Dwarf Galaxies, Cold Dark Matter, and Biased Galaxy Formation: 1986. By: Avishai Dekel and Joseph Silk Presented By: Luke Hovey. Correlations. Proposed Models. No Gas Loss Predicts a metallicity that is constant, which is wrong. Gas Removal in a Self-gravitating Cloud

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The Origin of Dwarf Galaxies, Cold Dark Matter, and Biased Galaxy Formation: 1986

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  1. The Origin of Dwarf Galaxies, Cold Dark Matter, and Biased Galaxy Formation: 1986 By: Avishai Dekel and Joseph Silk Presented By: Luke Hovey

  2. Correlations

  3. ProposedModels • No Gas Loss • Predicts a metallicity that is constant, which is wrong. • Gas Removal in a Self-gravitating Cloud • Fails to reproduce simultaneous decline of metallicity and surface brightness observed in faint dwarfs. • Gas Loss in a Dominant Halo • Predicts initial spectrum perturbations which correspond to CDM perturbations near 10^7 M_{\odot}

  4. Radius vs. Luminosity • Clear divide between the Dwarf Ellipticals (DEs) and the Dwarf Irregulars(DIs) • The DEs and DIs obey a tight correlation over 10 magnitudes • This is best fit by a L \propto R^4 power law

  5. Metallicity vs. Luminosity • The data are best fit by a L \propto Z^2 power law, but the Des are better fit by a Z^2.5 fit. • The model predicts a Z^2.7 behavior. The slope is a result of the presence of halos of CDM

  6. Velocity Dispersion vs. Luminosity • Central velocity dispersion thought to obey L \propto V^c, with 3<c<4.

  7. Mass to Light Ratio • Mass estimates have large errors • Preliminary results here are consistent with massive halos that dominate gravitational potential.

  8. Gas Number Density vs. Virial Velocity • Most “Normal Galaxies” must originate from 2-3 \sigma CDM perturbations • “Normal galaxies” Lie at larger virial velocities and higher densities • Diffusive Dwarfs have smaller virial velocities and lower densities with a mass around 10^9 M_{\odot}.

  9. Surface Brightness vs. Luminosity • “Normal Galaxies” May not be that normal!

  10. Conclusions • Low metallicity and surface brightness observed in faint dwarfs is indicative of substantial gas mass loss. • The model which best fit the data, is the model where gas clouds are embedded in massive halos. • The critical virial velocity seems to point towards two classes of elliptical galaxies. • Critical conditions for mass loss and cooling seem to point towards a bias towards dwarf galaxies. • Dwarf irregulars may be fundamentally the same as dwarf ellipticals except their mass loss was not as complete because they may have larger DM halos. • Dwarf galaxies may help probe large scale variations of mass distribution, and dwarf irregulars may play a key role in observations.

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