DARK MATTER IN GALAXIESNAME

INSTITUTE

Overview

The concept of Dark MatterDark Matter in Spirals, Ellipticals, dSphsDark Matter at outer radii. Global propertiesDirect and Indirect Searches of 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.

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 overdensities d.

Concentration c=R200/ rs is an

alternative density measure.

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

At low z, c decreases with mass.

-> Movie 1

Aquarius simulations, highest resolutions to date.

Results: Cuspy Einasto profiles (Navarro+10).

No difference for mass modelling with NFW ones

with a dependent slightly on mass.

Central surface brightness vs galaxy magnitude

The Realm of Galaxies

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

Spirals : stellar disk +bulge +HI disk

Ellipticals & dSph: stellar spheroidThe distribution of luminous matter :

SPIRALS

Stellar Disks

M33 - outer disk truncated, very smooth structure

NGC 300 - exponential disk goes for at least 10 scale-lengths

Bland-Hawthorn et al 2005Ferguson et al 2003

scaleradius

HI

Flattish radial distribution

Deficiency in centre

CO and H2

Roughly exponential

Negligible mass

Wong & Blitz (2002)

Gas surface densities

Circular velocities from spectroscopy

- Optical emission lines (H, NN a)

- Neutral hydrogen (HI)-carbon monoxide (CO)

Tracer angular spectral resolution resolution

HI 7" … 30" 2 … 10 km s-1

CO 1.5" … 8" 2 … 10 km s-1

HN, … 0.5" … 1.5" 10 … 30 km s-1

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0

50

100

150

200

250

V

R/Rd

UGC2405

ROTATION CURVES (RC) Symmetric circular rotation of a disk characterized by

• Sky coordinates of the galaxy centre

• Systemic velocity Vsys

• Circular velocity V(R)

• Inclination angle

N = azimuthal angle

b

ai arccos

iRVVV sysobs sincos)(),(

Example of a recent high quality RC: Radial coordinate in units of RD

V(2)

V(R/RD)

R/RD

Early discovery from optical and HI RCs

MASS DISCREPANCY AT OUTER RADII

disk

observed

NO RC FOLLOWS THE DISK VELOCITY PROFILE

Rubin et al 1980

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 1979Radius (kpc)

Evidence for a Mass Discrepancy

The distribution of gravitating matter is luminosity dependent.

Tully-Fisher relation exists at local level (radii Ri)

no DM slope

Yegorova et al 2007

Rotation Curves

Coadded from 3200 individual RCs

PSS

6 RD

mag.

TYPICAL INDIVIDUAL RC

low

high

The Concept of 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 observationsHow to extrapolate the URC out to virial radius?Needed

-> Movie 2

Extrapolating the URC to the Virial radius

Virial halo masses and VVIR are obtained - directly by weak-lensing - indirectly by correlating dN/dL with theoretical DM halo dN/dM

Shankar et al 2006

An Universal Mass Distribution

ΛCDM theoretical URC from NFW Observed URC profile and MMW theory

NFW

high

low

Salaucci+,2007

theory

obs

obs

Rotation curve analysisFrom data to mass models

➲ 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).

Vtot

2 = VDM

2 + Vdisk

2 + Vgas

2

core radius

halo central density

luminosity

disk

halo

halo

halo

diskdisk

MASS MODELLING RESULTS

fract

ion o

f D

M

lowest luminosities highest luminosities

All structural DM and LM parameters are related with luminosity.g

Smaller galaxies are denser and have a higher proportion of dark matter.

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 radiusrc rc

Kormendy & Freeman (2003)

No ~ LB- 0.35

rc ~ LB 0.37

N ~ LB 0.20

No

rc

N

The central surface density N ~ Norc =constant 3.0

2.5

2.0

1.5

1.0

The distribution of DM around spirals Using individual galaxies Gentile+ 2004, de Blok+ 2008  Kuzio de Naray+ 2008, Oh+  2008, Spano+ 2008, Trachternach+ 2008, Donato+,2009

A detailed investigation: high quality data and model independent analysis

NGC3621

- Non-circular motions are small.- No DM halo elongation- ISO halos often preferred over NFW

Tri-axiality and non-circular motions cannot explainthe CDM/NFW cusp/core discrepancy

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

DDO 47

SPIRALS: WHAT WE KNOW

AN UNIVERSAL CURVE REPRESENTS THE ALL INDIVIDUAL RCsMORE PROPORTION OF DARK MATTER IN SMALLER SYSTEMSRADIUS IN WHICH THE DM SETS IN FUNCTION OF LUMINOSITYMASS PROFILE AT LARGER RADII COMPATIBLE WITH NFWDARK HALO DENSITY SHOWS A CENTRAL CORE OF SIZE 2 RD

ELLIPTICALS

Surface brightness follows a Sersic (de Vaucouleurs) law

Re : the effective radius

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

The Stellar Spheroid

R Rr

drrrjdzrjRI

22

)(2)()(

ESO 540 -032

Sersic profile

Modelling Ellipticals

Measure the light profile

Derive the total mass profile from

Dispersion velocities of stars Planetary Nebulae

X-ray properties of the emitting hot gas

Combining weak and strong lensing data

Disentangle the dark and the stellar components

19.10.10

Line-of-sight, projected Velocity Dispersions, 2-D kinematics

SAURON data of N 2974

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

SDSS early-type galaxies

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

→ M/L not constant ~ L0.14

From virial theorem

The FP “tilt” is due to variations in: Dark matter fraction? Stellar population? Likely.

Bernardi et al. 2003

Shankar & Bernardi 2009

Hyde & Bernardi 2009

Stars dominate inside Re

Dark matter profile unresolved

Mamon & Łokas 05

Assumed IsotropyThree components: DM, stars, Black Holes

Dark-Luminous mass decomposition of dispersion velocities

Weak and strong lensing

SLACS: Gavazzi et al. 2007)

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

Gavazzi et al 2007

Mass Profiles from X-ray

Temperature

Density

Hydrostatic Equilibrium

M/L profile

NO DM

Nigishita et al 2009

ELLIPTICALS: WHAT WE KNOW

A LINK AMONG THE STRUCTURAL PROPERTIES OF STELLAR SPHEROIDSMALL AMOUNT OF DM INSIDE RE

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

19.10.10

dSphs

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

Large 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 2009

Kinematics of dSph1983: 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

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

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

Dispersion velocity profiles

dSph dispersion profiles generally remain flat to large radii

Wilkinson et al 2009

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

Degeneracy between DM mass profile and velocity anisotropyCusped and cored mass models fit dispersion profiles equally well

However: dSphs cored distribution structural parameters agree with those of Spirals and Ellipticals

Halo central density vs core radius

Walker et al 2009

Donato et al 2009

Global trend of dSph haloes

• SculptorAndII

Mateo et al 1998

Gilmore et al 2007

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 THE EXTRAPOLATION OF THE URC HINTS FOR THE PRESENCE OF A DENSITY CORE

The stellar mass of galaxiesThe luminous matter in the form of stars M* is a crucial quantity.Indispensable to infer the amount of Dark Matter M*/L of a galaxy obtained via Stellar Population Synthesis models

Fitted SED

Dynamical and photometric estimates agree

WEAK LENSING

Weak Lensing around galaxies

Critical surface density

Lensing equation for the observed tangential shear

Donato et al 2009

HALO MASSES ARE A FUNCTION OF LUMINOSITY

Mandelbaum et al 2009

Walker+ 2010

Mass correlates with luminosityURC mass profile Mh(r) = F(r/Rvir, Mvir) valid

for S, dSph, LSB, checking for E

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

Unique value of halo central surface density

Salucci+ 2007

Donato et al. 2009

Walker+ 2010

GALAXY HALOS: WHAT WE KNOW

Mandelbaum,+ 06

DETECTING DARK MATTER

Anti-proton spectrum

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

This leads to essential information on:

the very nature of dark matter

the galaxy formation process

Baryon +DM Simulations should eventually reproduce

Shallow DM inner distribution, the observed relationships between the halo mass and 1) central halo density, 2) baryonic mass, 3) half-mass baryonic radius and 4) baryonic central surface density, a constant central halo surface density.

Theory, phenomenology, simulations, experiments should play a balanced role in the search for dark matter and its role.