Materia oscura e gas anomalo nella galassia a spirale 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
Rotation curve and mass model
Vertical structure and kinematics of the HI disk
•
Cold disk and anomalous gas
• Models
Conclusions and future work
Dark and luminous matter

V R
R
2
Direct estimate of the mass
distribution (in spiral galaxies)
dynamical mass
Luminosity profile of spiral
galaxies are approximately
Surface density
distribution?
I ( R)  I 0 exp(  R / h)
M
I ( R)   ( R)
L
luminous mass
V 2  (Gh 0 )[ I 0 (r / 2) K 0 (r / 2)  I1 (r / 2) K1 (r / 2)]r 2
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
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
1. HI observations of NGC 4559
Optical
image
HI total
map
Radio
continuum
Velocity
field
2. Rotation curve and mass model
Tilted ring model , see Begeman (1987)
V  Vsys  V ( R) sin i cos 
 ( x  x0 ) sin   ( y  y0 ) cos 
cos  
R
 ( x  x0 ) cos   ( y  y0 ) sin 
cos  
R cos i
2. Rotation curve and mass model
the surface density distribution
cannot explain
the observed rotation curve
DARK MATTER IS REQUIRED
2. Rotation curve and mass model
V ≈ constant (flat), so the enclosed mass M(R)  R
  R
 ( R)   0 1  
  Rc



2



1
where 0 is the central density and Rc is the core radius
•The luminous component cannot explain the
observed rotation curve
Vertical structure and
kinematics of the HI disk
Vertical kinematics
NGC 6946
optical image
total HI map
Boomsma et al. (2002)
Vertical structure
NGC 891
optical image + total HI map
Swaters et al. (1997)
Vertical structure and kinematics
NGC 2403
Fraternali (2001)
HI total map
NGC 4559
This work
1. Cold disk and anomalous gas
NGC 2403
Fraternali (2001)
1. Cold disk and anomalous gas
Why study NGC 4559?
1. Cold disk and anomalous gas
HI total map
of the cold disk
Velocity field
of the cold disk
HI total map
of the anomalous gas
Velocity field
of the anomalous gas
1. Cold disk and anomalous gas
 20 km/s
Rotation curve of the
cold disk
(1)
 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
2. Models
One-component structure
Two-component structure
corotation
no corotation
•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
What is the origin of the anomalous gas?
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)
2. Infall of extragalactic, probably primordial, gas
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?
The end
One component structure
Two component structure
(corotation)
Two component structure
(no corotation)
Modified Newtonian Dynamics
The gravitational field g
replaces the standard Newtonian field gn following
(g/a0) = gn
 1
 ( g / a0 )  
 g / a0
a0 = 10-8 cm/s2
g  a0
g a0

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