Dark matter and anomalous gas

in the spiral galaxyNGC 4559

Claudia Veronica Barbieri

Relatore interno: G. BertinRelatore esterno: R. Sancisi

Correlatori: F. Fraternali T. Oosterloo

Outline

• HI observations of NGC 4559• Rotation curve and mass model

Dark and luminous matter

Vertical structure and kinematics of the HI disk

• Cold disk and anomalous gas• Models

Conclusions and future work

Dark and luminous matter

RRV

2 Direct estimate of the mass distribution (in spiral galaxies)

dynamical mass

Luminosity profile of spiral galaxies are

approximately

)()( RL

MRI

)/exp()( 0 hRIRI

luminous mass

Surface density distribution?

211000

2 )]2/()2/()2/()2/()[( rrKrIrKrIGhV

where r = R/h and the I e K denote standard Bessel functions

V2max= 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)

iR

yyxxR

yyxx

iRVVV sys

cos

sin)(cos)(cos

cos)(sin)(cos

cossin)(

00

00

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

12

0 1)(

cR

RR

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

total HI mapoptical image

Boomsma et al. (2002)

NGC 6946Vertical kinematics

Vertical structure

total HI map

optical image +

Swaters et al. (1997)

NGC 891

Fraternali (2001)

This work

Vertical structure and kinematics

NGC 2403 NGC 4559HI total map

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

Velocity field of the anomalous

gas

HI total mapof the anomalous

gas

HI total mapof the cold disk

Velocity field of the cold disk

1. Cold disk and anomalous gas

Rotation curve of the cold disk

(1)

Rotation curve of the anomalous

gas(2)

60 km/s

20 km/s

M1 = 6.7 109 M

R1 = 24.5 kpcM2 = 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?

2. Infall of extragalactic, probably primordial, 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.

Future work

•Observing NGC 4559 at other wavelengthsDoes 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 galaxyCould 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

(g/a0) = gn

0

0

00 /

1)/(

ag

ag

agag

a0 = 10-8 cm/s2

The gravitational field g replaces the standard Newtonian field gn following