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Dark matter and anomalous gas in the spiral galaxy NGC 4559

Dark matter and anomalous gas in the spiral galaxy NGC 4559. Claudia Veronica Barbieri. Relatore interno: G. Bertin Relatore esterno: R. Sancisi Correlatori: F. Fraternali T. Oosterloo. Outline. Dark and luminous matter. HI observations of NGC 4559

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Dark matter and anomalous gas in the spiral galaxy NGC 4559

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  1. Dark matter and anomalous gasin the spiral galaxyNGC 4559 Claudia Veronica Barbieri Relatore interno: G. Bertin Relatore esterno: R. Sancisi Correlatori: F. Fraternali T. Oosterloo

  2. Outline Dark and luminous matter • HI observations of NGC 4559 • Rotation curve and mass model Vertical structure and kinematics of the HI disk • Cold disk and anomalous gas • Models Conclusions and future work

  3. Dark and luminous matter

  4. Direct estimate of the mass distribution (in spiral galaxies) dynamical mass Luminosity profile of spiral galaxies are approximately Surface density distribution? luminous mass

  5. where r = R/h and the I e K denote standard Bessel functions V2 max= 0.8  G 0 h at R/h  2.2

  6. M/L = 3.8 M/L van Albada et al. (1985) THE LACK OF THE KEPLERIAN DECLINE IS THE MAIN DIRECT EVIDENCE FOR THE EXISTENCE OF DARK MATTER HALOS

  7. Optical image Radio continuum Velocity field HI total map 1. HI observations of NGC 4559

  8. 2. Rotation curve and mass model Tilted ring model , see Begeman (1987)

  9. the surface density distribution cannot explain the observed rotation curve DARK MATTER IS REQUIRED 2. Rotation curve and mass model

  10. V ≈ constant (flat), so the enclosed mass M(R) R where 0 is the central density and Rc is the core radius 2. Rotation curve and mass model

  11. The luminous component cannot explain the observed rotation curve

  12. Vertical structure and kinematics of the HI disk

  13. NGC 6946 optical image total HI map Boomsma et al. (2002) Vertical kinematics

  14. optical image + total HI map NGC 891 Swaters et al. (1997) Vertical structure

  15. Vertical structure and kinematics HI total map NGC 2403 NGC 4559 Fraternali (2001) This work

  16. NGC 2403 Fraternali (2001) 1. Cold disk and anomalous gas

  17. 1. Cold disk and anomalous gas Why study NGC 4559?

  18. HI total map of the anomalous gas HI total map of the cold disk Velocity field of the anomalous gas Velocity field of the cold disk 1. Cold disk and anomalous gas

  19. Rotation curve of the cold disk (1)  20 km/s  60 km/s Rotation curve of the anomalous gas (2) M1 = 6.7  109 M R1 = 24.5 kpc M2 = 5.9  108 M R2 = 21.5 kpc 1. Cold disk and anomalous gas

  20. One-component structure corotation no corotation 2. Models Two-component structure

  21. The anomalous gas cannot be explained by inclination and/or pure thickness effects along the line of sight • It is associated with a thick HI layer with a mean rotation velocity lower than that of the disk • It is more evident on the S-E side

  22. 1. Galactic fountain A ionized gas, ejected by SN explosions and stellar winds, rieses above the disk, cools and falls back to the plane. (Bregman J.N., 1980) What is the origin of the anomalous gas? 2. Infall of extragalactic, probably primordial, gas

  23. Future work • Observing NGC 4559 at other wavelengths • Does a connection exist between the HI anomalous gas, the ionized gas (H), and the diffuse thermal emission (X-rays) as expected in the galactic fountain model? • Studying the small scale structure of this galaxy • Could the HI holes and the superbubbles (as observed in NGC 6946) be connected with the origin of the halo anomalous gas observed in NGC 4559? • Studying other spiral galaxies • Is the anomalous gas a common feature in spiral galaxies? • Does a relation exist between the presence of the anomalous • gas and the star formation activity?

  24. The end

  25. One component structure

  26. Two component structure (corotation)

  27. Two component structure (no corotation)

  28. Modified Newtonian Dynamics The gravitational field g replaces the standard Newtonian field gn following (g/a0) = gn a0 = 10-8 cm/s2

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