Dec. 1-8, 2010 - PowerPoint Presentation

Slide1

Dec. 1-8, 2010

DARK MATTER IN GALAXIES

Alessandro Romeo

Onsala Space Observatory

Chalmers University of Technology

SE-43992 Onsala, SwedenSlide2

Overview

Dark

m

atter

in SPIRALS

Dark matter in ELLIPTICALS

Dark matter in DWARF SPHEROIDALS

Detecting dark matter

ConclusionsSlide3

SPIRALS Slide4

Stellar

Discs

M33

very

smooth

structure

NGC 300

- exponential

disc

goes for at least 10 scale-

lengths

Bland-Hawthorn

et

al 2005

Ferguson

et al 2003

scale

radiusSlide5

HI

Flattish

radial distribution

Deficiency

in the

centre

CO

and

H

2

R

oughly

exponential Negligible mass

Wong

& Blitz (2002)

Gas

surface

densities

GAS DISTRIBUTION Slide6

Early

discovery from

optical and HI RCs

Mass discrepancy AT

LARGE

RADII

disk

observed

no

RC

follows

the disk

velocity

profile

Rubin

et

al 1980

diskSlide7

The mass

discrepancy

emerges

as

a

disagreement

between

light and mass

distributions

GALEX

SDSS

Extended

HI

kinematics

traces

dark

matter

-

-

NGC 5055

Light (SDSS)

HI

velocity

field

Bosma

, 1981

Bosma

, 1981

Bosma

1979

Radius

(

kpc

)Slide8

Rotation

Curves

Coadded

from

3200

individual

RCs

Salucci+07

6 R

D

mag

TYPICAL INDIVIDUAL

RCs

OF INCREASING

LUMINOSITY

Low

lum

high

lum

Slide9

The Concept of

Universal Rotation Curve (URC)

The

Cosmic Variance of the value of

V

(

x

,

L

) in

galaxies

of the

same

luminosity

L at the same radius x

=R/RD is negligible compared to the variations that V(x,L) shows as x and L vary.

The URC out

to

6 RD

is derived

directly from observationsExtrapolation of

URC out

to

virial

radius

by

using

Slide10

A Universal Mass

Distribution

ΛCDM URC

Observed

URC

NFW

high

low

Salucci+,2007

theory

obs

obsSlide11

Rotation curve analysis

From

data

to mass models

from

I-band

photometry

from HI observations Dark halos with constant density cores

(Burkert)

Dark

halos with cusps (NFW, Einasto)

The mass

model

has

3 free

parameters

: disk

mass,

halo

central

density

and

core

radi

radius

(

halo

length-scale

).

V

tot

2

= V

DM

2

+ V

disk

2

+ V

gas

2

NFW

BurkertSlide12

core

radius

halo

central

density

luminosity

disk

halo

halo

halo

disk

disk

MASS MODELLING RESULTS

fraction

of

DM

lowest

luminosities

highest

luminosities

All structural DM and LM

parameters are related

to luminosity.

g

Smaller

galaxies

are

denser

and

have

a

higher

proportion

of

dark

matter

.Slide13

Dark Halo

Scaling Laws

There

exist

relationships

between

halo

structural

quantiies and luminosity. Investigated

via mass modelling of individual galaxies

- Assumption:

Maximun

Disk, 30 objects-the slope of

the halo rotation curve near the center gives the halo core

density

-

extended RCs provide an estimate of

halo

core

radius

r

c

Kormendy

& Freeman (2004)



o

~ L

B

-

0.35

r

c

~ L

B

0.37



~

L

B

0.20



o

r

c



The

central

surface

density



~



o

r

c

=constant

3.0

2.5

2.0

1.5

1.0Slide14

SPIRALS: WHAT WE KNOW A UNIVERSAL CURVE REPRESENTS ALL THE INDIVIDUAL RCsMORE PROPORTION OF DARK MATTER IN SMALLER SYSTEMS

RADIUS AT WHICH THE DM SETS IN FUNCTION OF LUMINOSITYMASS PROFILE AT LARGER RADII COMPATIBLE WITH NFW

DARK HALO DENSITY SHOWS A CENTRAL CORE OF SIZE 2 R

DSlide15

ELLIPTICALSSlide16

Surface

brightness

of ellipticals

follows a Sersic (de

Vaucouleurs) law

R

e

: the

effective

radius

B

y

deprojecting I(R) we obtain the luminosity density j(r):

The Stellar

Spheroid

ESO 540 -032Sersic

profileSlide17

SDSS

early-type

galaxies

The

Fundamental

Plane: central velocity dispersion, half-light radius and surface brightness are related

From

virial

theorem

FP

“tilt”

due

to

variations with σ0

of: D

ark matter fraction

?

Stellar population?

Hyde

& Bernardi 2009

Fitting

gives: a=1.8 , b~-0.8)

then

:

Bernardi

et

al. 2003Slide18

RESULTSThe spheroid determines the velocity dispersion

Stars dominate

inside R

eMore complications when:presence of anisotropies

different halo profile (e.g. Burkert

)

Two components: NFW halo

,

Sersic

spheroid

Assumed isotropy

Dark-Luminous mass decomposition

of

velocity dispersions

Not a unique model – example: a giant elliptical with reasonable parameters

Mamon

&

Łokas

05

Dark

matter

profile unresolved

10

11Slide19

Weak

and

strong lensing

SLACS

: Gavazzi et al. 2007)

Inside R

e

, the total (

spheroid

+ dark

halo

) mass

increases

proportionally

to the radius Gavazzi

et al 2007

UNCERTAIN DM DENSITY PROFILE

I Slide20

Mass

Profiles

from X-ray

Temperature

Density

Hydrostatic

Equilibrium

M/L

profile

NO DM

Nigishita

et

al 2009

CORED HALOS?Slide21

ELLIPTICALS: WHAT WE KNOW A LINK AMONG THE STRUCTURAL PROPERTIES OF STELLAR SPHEROIDSMALL AMOUNT OF DM INSIDE R

E

MASS PROFILE COMPATIBLE WITH NFW AND BURKERTDARK MATTER DIRECTLY TRACED OUT TO R

VIRSlide22

dSphsSlide23

Low-luminosity, gas-free satellites of Milky Way and M31Large mass-to-light ratios (10 to 100 ), smallest stellar systems containing dark matter

Dwarf

spheroidals

: basic properties

Luminosities and sizes of

Globular Clusters and

dSph

Gilmore

et

al 2009Slide24

Velocity dispersion profiles

dSph dispersion profiles generally remain flat up to

large radii

Wilkinson

et al 2009

STELLAR SPHEROIDSlide25

Mass profiles of dSphs

Jeans equation relates kinematics,

light and underlying mass

distributionMake assumptions on the velocity anisotropy

and then fit the dispersion profile

Results point to cored distributions

Jeans

’ models

provide

the most

objective sample

comparison

Gilmore

et

al 2007

DENSITY PROFILE

n

(R)

PLUMMER PROFILESlide26

Degeneracy between DM mass profile and velocity anisotropy

Cusped and cored mass models fit dispersion profiles equally well

However

:

dSphs

c

ored

model

structural

parameters

agree with those of Spirals and Ellipticals

Halo

central density vs core radius

σ(R) km/s

Donato

et al 2009

Walker

et

al 2009

NFW+anisotropy

= COREDSlide27

DSPH: WHAT WE KNOW PROVE THE EXISTENCE OF DM HALOS OF 1010

MSUN

AND ρ

0 =10-

21 g/cm3

DOMINATED BY DARK MATTER AT ANY RADIUS

MASS PROFILE CONSISTENT WITH AN EXTRAPOLATION OF THE URC

HINTS FOR THE PRESENCE OF A DENSITY CORE

Slide28

DETECTING DARK MATTERSlide29
Slide30

DMSlide31

CONCLUSIONSThe distribution of DM halos around galaxies shows a striking and complex phenomenology.

Observations and experiments, coupled with theory and simulations, will (hopefully) soon allow us to understand two fundamental issues:

The nature of dark matter itself

The process of galaxy formationSlide32

Thanks …..That’s enough with Dark Matter!Switch on the light ;-)19.10.10