DARK MATTER IN GALAXIES
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DARK MATTER IN GALAXIES. Alessandro Romeo. Onsala Space Observatory Chalmers University of Technology SE-43992 Onsala, Sweden. Dec. 1-8, 2010. Overview Dark m atter in SPIRALS Dark matter in ELLIPTICALS Dark matter in DWARF SPHEROIDALS Detecting dark matter Conclusions.

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DARK MATTER IN GALAXIES

Alessandro Romeo

Onsala Space Observatory

Chalmers University of Technology

SE-43992 Onsala, Sweden

Dec. 1-8, 2010


Overview

Dark matter in SPIRALS

Dark matter in ELLIPTICALS

Dark matter in DWARF SPHEROIDALS

Detecting dark matter

Conclusions



Stellar Discs

M33verysmoothstructure

NGC 300 - exponential disc

goes for at least 10 scale-

lengths

scale

radius

Bland-Hawthornet al 2005

Ferguson et al 2003


Wong & Blitz (2002)

Gas surfacedensities

GAS DISTRIBUTION

HI

Flattishradialdistribution

Deficiency in the centre

CO and H2

Roughlyexponential

Negligible mass


Earlydiscoveryfromoptical and HI RCs

observed

disk

no RC followsthe disk velocityprofile

disk

Rubinet al 1980

Mass discrepancy AT LARGE RADII


Extended HI kinematicstraces dark matter

-

-

Light (SDSS)

HI velocityfield

  • NGC 5055

SDSS

Bosma, 1981

GALEX

Bosma, 1981

Radius (kpc)

Bosma 1979

The mass discrepancyemergesas a disagreementbetween light and mass distributions


mag

Salucci+07

6 RD

Rotation Curves

Coaddedfrom 3200 individualRCs

TYPICAL INDIVIDUAL RCs OF INCREASING

LUMINOSITY

Low lum

high lum


The Concept of Universal Rotation Curve (URC)

The Cosmic Variance of the value of V(x,L) in galaxies of the same luminosityL at the sameradius x=R/RD is negligible compared to the variations that V(x,L) shows as xandL vary.

The URC out to 6 RD isderiveddirectlyfromobservations

Extrapolationof URC out tovirialradiusbyusing


A Universal Mass Distribution

ΛCDM URC Observed URC

NFW

theory

low

obs

high

obs

Salucci+,2007


Rotation curve analysis

From data to mass models

Vtot2 = VDM2 + Vdisk2 + Vgas2

  • fromI-bandphotometry

  • from HI observations

    Dark haloswithconstant density cores (Burkert)

    Dark haloswithcusps(NFW, Einasto)

    The mass modelhas 3 free parameters: disk mass, halocentral density and core radi radius (halolength-scale).

NFW

Burkert


halocentral density

coreradius

luminosity

MASS MODELLING RESULTS

highestluminosities

lowestluminosities

halo

disk

disk

halo

halo

disk

All structural DM and LM

parameters are related

to luminosity.g

Smallergalaxies are denser and have a higherproportionof dark matter.

fractionof DM


Dark HaloScalingLaws

Thereexistrelationshipsbetweenhalostructuralquantiies and luminosity.

Investigated via mass modellingofindividualgalaxies

- Assumption:MaximunDisk, 30 objects

-the slopeof the halo rotation curve near the center givesthe halocore density

- extendedRCsprovidean estimate ofhalocoreradiusrc

  • Kormendy & Freeman (2004)

o

o ~ LB- 0.35

rc ~ LB0.37

 ~LB0.20

rc

The centralsurfacedensity  ~ orc=constant

3.0

2.5

2.0

1.5

1.0


SPIRALS: WHAT WE KNOW

A UNIVERSAL CURVE REPRESENTS ALL THE INDIVIDUAL RCs

MORE PROPORTION OF DARK MATTER IN SMALLER SYSTEMS

RADIUS AT WHICH THE DM SETS IN FUNCTION OF LUMINOSITY

MASS PROFILE AT LARGER RADII COMPATIBLE WITH NFW

DARK HALO DENSITY SHOWS A CENTRAL CORE OF SIZE 2 RD



The Stellar Spheroid

Surfacebrightnessofellipticalsfollows a Sersic (de Vaucouleurs) law

Re : the effectiveradius

  • Bydeprojecting I(R) weobtain the luminosity density j(r):

ESO 540 -032

Sersicprofile


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

SDSS early-typegalaxies

Bernardi et al. 2003

Fromvirialtheorem

Hyde & Bernardi 2009

Fitting

gives: a=1.8 , b~-0.8)

then:

FP “tilt” due tovariationswithσ0of:

Dark matterfraction?

Stellar population?


RESULTSThe spheroid determines the velocity dispersionStars dominate inside ReMore complications when:presence of anisotropiesdifferent halo profile (e.g. Burkert)

1011

Two components: NFW halo, Sersic spheroid Assumed isotropy

Mamon& Łokas05

Dark matterprofileunresolved


Weak and strong lensing
Weakand strong lensing

SLACS: Gavazzi et al. 2007)

Gavazzi et al 2007

Inside Re, the total (spheroid + dark halo) mass increasesproportionallyto the radius

UNCERTAIN DM DENSITY PROFILEI


Mass ProfilesfromX-ray

Nigishitaet al 2009

Temperature

Density

M/L profile

NO DM

HydrostaticEquilibrium

  • CORED HALOS?


ELLIPTICALS: WHAT WE KNOW

A LINK AMONG THE STRUCTURAL PROPERTIES OF STELLAR SPHEROID

SMALL AMOUNT OF DM INSIDE RE

MASS PROFILE COMPATIBLE WITH NFW AND BURKERT

DARK MATTER DIRECTLY TRACED OUT TO RVIR



Dwarf spheroidals basic properties
Dwarf spheroidals: basic properties

  • Low-luminosity, gas-free satellites of Milky Way and M31

  • Large mass-to-light ratios (10 to 100 ), smallest stellar systems containing dark matter

Luminosities and sizes of

Globular Clusters and dSph

Gilmoreet al 2009


Velocity dispersion profiles
Velocity dispersion profiles

STELLAR SPHEROID

Wilkinson et al 2009

dSph dispersion profiles generally remain flat up to large radii


Mass profiles of dsphs
Mass profiles of dSphs

Jeans’ models provide the most objective sample comparison

  • Jeans equation relates kinematics, light and underlying mass distribution

  • Make assumptions on the velocity anisotropy and then fit the dispersion profile

n(R)

PLUMMER PROFILE

DENSITY PROFILE

Results point to cored distributions

Gilmoreet al 2007


Degeneracy between DM mass profile and velocity anisotropy

Cusped and cored mass models fit dispersion profiles equally well

Walkeret al 2009

However:

dSphscoredmodelstructuralparametersagreewiththoseofSpirals and Ellipticals

σ(R) km/s

Halocentral density vs coreradius

NFW+anisotropy = CORED

Donato et al 2009


DSPH: WHAT WE KNOW

PROVE THE EXISTENCE OF DM HALOS OF 1010 MSUN AND ρ0 =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




Conclusions

CONCLUSIONS

The 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 formation


Thanks
Thanks …..

  • That’s enough with Dark Matter!

  • Switch on the light ;-)


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