1. 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

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

5. where r = R/h and the I e K denote standard Bessel functionsV2
max= 0.8  G 0 h at R/h  2.2

6. THE LACK OF THE KEPLERIAN DECLINE IS THE MAIN DIRECT EVIDENCE FOR
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. 1. HI observations of NGC 4559
Optical
image
Radio
continuum
Velocity
field
HI total
map

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

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

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

11. The luminous component cannot explain the observed rotation curve

12. Vertical structure and kinematics of the HI disk

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

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

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

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

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

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

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

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

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

23. Observing NGC 4559 at other wavelengths
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

26. One component structure

27. Two component structure
(corotation)

28. Two component structure
(no corotation)

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