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DARK MATTER IN GALAXIES Jianling Gan Shanghai Astronomical Observatory http://www.sissa.it/ap/dmg/index.html. Dec. 1-8, 2010. Overview The concept of Dark Matter Dark Matter in Spirals , Ellipticals , dSphs Dark Matter at outer radii . Global properties

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slide1
DARK MATTER IN GALAXIES

Jianling Gan

Shanghai Astronomical Observatory

http://www.sissa.it/ap/dmg/index.html

Dec. 1-8, 2010

slide2
Overview

The conceptof Dark Matter

Dark Matter in Spirals, Ellipticals, dSphs

Dark Matter at outerradii. Global properties

Directand IndirectSearchesof Dark Matter

what is dark matter
What is Dark Matter?

In a galaxy, the radial profile of the gravitating matter M(r) and that of the sum of all luminous components ML(r) do not match.

A MASSIVE DARK COMPONENT is introduced to account for the disagreement:

Its profile MH(r) must obey:

The DM phenomenon can be investigated only if we accurately meausure the distribution of:

Luminous matter.

Gravitating matter.

slide4
The Realm of Galaxies

The range of galaxies in magnitude, types and central surface density : 15 mag, 4 types, 16 mag arsec2

Centralsurfacebrightness vs galaxymagnitude

Spirals : stellar disk +bulge +HI disk

Ellipticals & dSph: stellar spheroid

The distribution of luminous matter :

slide6
Stellar Disks

M33 - outer disk truncated,

very smooth structure

NGC 300 - exponential disk

goes for at least 10 scale-

lengths

scale

radius

Bland-Hawthorn et al 2005

Ferguson et al 2003

slide7
Wong & Blitz (2002)

Gas surface densities

HI

Flattish radial distribution

Deficiency in centre

CO and H2

Roughly exponential

Negligible mass

slide8
Circularvelocitiesfromspectroscopy

- Opticalemissionlines (H, Na)

- Neutralhydrogen (HI)-carbonmonoxide (CO)

Tracer angular spectral resolution resolution

HI 7" … 30" 2 … 10 km s-1

CO 1.5" … 8" 2 … 10 km s-1

H, … 0.5" … 1.5" 10 … 30 km s-1

slide9
ROTATION CURVES (RC)
  • Symmetriccircular rotation of a disk characterizedby
  • Sky coordinatesof the galaxycentre
  • SystemicvelocityVsys
  • CircularvelocityV(R)
  • Inclination angle

 = azimuthal angle

Exampleof a recent high quality RC:

Radial coordinate in unitsof RD

V(R/RD)

V(2)

R/RD

slide10
Early discovery from optical and HI RCs

observed

disk

no RC follows the disk velocityprofile

Rubinet al 1980

Mass discrepancy AT OUTER RADII

slide11
Extended HI kinematicstraces dark matter

-

-

Light (SDSS)

HI velocity field

NGC 5055

SDSS

Bosma, 1981

GALEX

Bosma, 1981

Radius (kpc)

Bosma 1979

The mass discrepancyemergesas a disagreementbetween light and mass distributions

slide12
Evidencefor a Mass Discrepancy

The distributionofgravitatingmatterisluminositydependent.

Tully-Fisher relation existsat locallevel (radiiRi)

no DM slope

Yegorova et al 2007

slide13
Dark Matter Profiles from N-body simulations

In ΛCDM scenario the density profile for virialized DM halos of all masses of all masses is empirically described at all times by the universal NFW formula (Navarro+96,97).

More massive and halos formed

earlier have larger overdensitiesd.

Concentration c=R200/ rsis an

alternative density measure.

slide14
The concentration scales with mass and redshift (Zhao+03,08; Gao+08, Klypin+10):

At low z, c decreases with mass.

-> Movie 1

slide15
Aquarius simulations, highest resolutions to date.

Results: CuspyEinasto profiles (Navarro+10).

No difference for mass modelling with NFW ones

with a dependent slightly on mass.

slide16
mag.

PSS

6 RD

Rotation Curves

Coaddedfrom 3200 individualRCs

TYPICAL INDIVIDUAL RC

low

high

slide17
The Conceptof the Universal Rotation Curve (URC)

The Cosmic Variance of the value of V(x,L) in galaxies of 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 varies.

The URC out to 6 RD is derived directly from observations

How to extrapolate the URC out to virial radius?

Needed

-> Movie 2

slide18
Extrapolating the URC to the Virial radius

Shankar et al 2006

Virial halo masses and VVIR are obtained

- directly by weak-lensing

- indirectly by correlating dN/dL with theoretical DM halo dN/dM

slide19
An Universal Mass Distribution

ΛCDM theoretical URC from NFW Observed URC

profileand MMW theory

NFW

theory

low

obs

high

obs

Salaucci+,2007

slide20
Rotation curve analysis

From data to mass models

Vtot2 = VDM2 + Vdisk2 + Vgas2

  • from I-band photometry
  • from HI observations

Dark halos with constant density cores

Dark halos with cusps (NFW, Einasto)

Model has three free parameters: disk mass, halo central density and core radius (halo length-scale).

slide21
halocentral density

coreradius

luminosity

MASS MODELLING RESULTS

highest luminosities

lowest luminosities

halo

disk

disk

halo

halo

disk

Allstructural DM and LM

parameters are related

withluminosity.g

Smallergalaxies are denser and have a higherproportionof dark matter.

fractionof DM

slide22
Dark HaloScalingLaws

There exist relationships between halo structural quantiies and luminosity.

Investigated via mass modelling of individual galaxies

- Assumption:MaximunDisk, 30 objects

-the slopeof the halo rotation curve near the center givesthe

halocore density

- extendedRCsprovidean estimate ofhalocoreradiusrcrc

Kormendy & Freeman (2003)

o

o ~ LB- 0.35

rc ~ LB0.37

 ~LB0.20

rc

The central surface density  ~ orc=constant

3.0

2.5

2.0

1.5

1.0

slide23
The distributionof DM aroundspirals

UsingindividualgalaxiesGentile+ 2004, de Blok+ 2008  Kuzio de Naray+ 2008, Oh+  2008, Spano+ 2008, Trachternach+ 2008, Donato+,2009

A detailedinvestigation: high quality data and modelindependentanalysis

slide24
DDO 47

NGC3621

General results from several samples including THINGS, HI survey of uniform and high quality data

- Non-circularmotions are small.

- No DM haloelongation

- ISO halosoftenpreferredover NFW

Tri-axiality and non-circularmotionscannotexplain

the CDM/NFW cusp/corediscrepancy

slide26
The Stellar Spheroid

Surface brightness follows a Sersic (de Vaucouleurs) law

Re : the effective radius

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

ESO 540 -032

Sersicprofile

modelling ellipticals

Modelling Ellipticals

Measure the light profile

Derive the total mass profilefrom

DispersionvelocitiesofstarsPlanetaryNebulae

X-raypropertiesof the emitting hot gas

Combiningweak and strong lensing data

Disentangle the dark and the stellar components

slide29
The Fundamental Plane: central dispersion velocity, half light radius and central surface brightness are related

Bernardi et al. 2003

SDSS early-type galaxies

Fromvirialtheorem

  • Fitting r ~ a Ib gives: (a<2, b~0.8)

→ M/L not constant

~ L0.14

Hyde & Bernardi 2009

Shankar & Bernardi 2009

The FP “tilt” is due to variations in:

Dark matter fraction?

Stellar population? Likely.

stars dominate inside r e dark matter profile unresolved
Stars dominate inside ReDark matterprofileunresolved

Dark-Luminous mass decomposition of dispersion velocities

Assumed IsotropyThree components: DM, stars, Black Holes

Mamon & Łokas 05

weak and strong lensing
Weakand strong lensing

SLACS: Gavazzi et al. 2007)

Gavazzi et al 2007

Inside R_e, the total (spheroid + dark halo) mass increases in proportionto the radius

slide32
Mass Profiles from X-ray

Nigishita et al 2009

Temperature

Density

M/L profile

NO DM

Hydrostatic Equilibrium

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

Gilmore et al 2009

kinematics of dsph
Kinematics of dSph
  • 1983: Aaronson measured velocity dispersion of Draco based on observations of 3 carbon stars - M/L ~ 30 1997: First dispersion velocity profile of Fornax (Mateo)2000+: Dispersion profiles of all dSphs measured using multi-object spectrographs

Instruments: AF2/WYFFOS (WHT, La Palma); FLAMES (VLT); GMOS (Gemini); DEIMOS (Keck); MIKE (Magellan)

2010: full radial coverage in each dSph, with 1000 stars per galaxy

dispersion velocity profiles
Dispersion velocity profiles

Wilkinson et al 2009

dSph dispersion profiles generally remain flat to large radii

mass profiles of dsphs
Mass profiles of dSphs

Jeans equation relates kinematics, light and underlying mass distribution

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

Results point to cored distributions

Jeans’ models provide the most objective sample comparison

slide38
Degeneracy between DM mass profile and velocity anisotropy

Cusped and cored mass models fit dispersion profiles equally well

However:

dSphscoreddistributionstructuralparametersagreewiththoseofSpirals and Ellipticals

Halocentral density vs coreradius

Walker et al 2009

Donato et al 2009

global trend of dsph haloes
Global trend of dSph haloes
  • Sculptor

AndII

Mateo et al 1998

Gilmore et al 2007

slide40
The stellar mass of galaxies

The luminousmatterin the formofstarsM*is a crucialquantity.

Indispensabletoinfer the amountof Dark Matter

M*/L ofa galaxyobtainedvia Stellar PopulationSynthesismodels

Fitted SED

Dynamical and photometric estimates agree

slide42
Weak Lensing around galaxies

Criticalsurface density

  • Lensingequationfor the observedtangentialshear

Donato et al 2009

slide43
Mandelbaum et al 2009

HALO MASSES ARE A FUNCTION OF LUMINOSITY

slide44
Comparing DM halos of Spirals, LSBs & dSphs

URC-halo mass profile Mh(r) = F(r/Rvir, Mvir)

Unique halo mass profile Mh(r) = G(r)

Unique value of halo central surface density

Salucci+ 2007

Walker+ 2010

Walker+ 2010

Donato et al. 2009

conclusions

CONCLUSIONS

The distribution of the gravitating matter in galaxies shows a striking and complex observational phenomenology.

This is likely to hold essential information on:

the very nature of dark matter

the galaxy formation process

Theory, observational phenomelogy and simulation should play a balanced role in the search for dark matter and its role.

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