dark matter in galaxieslapi/dmaw/dmaw2010_final.pdf · 2013-04-17 · dark matter in galaxies...
TRANSCRIPT
Dark Matter Awareness Week December, 1-8, 2010
Dark Matter in Galaxies
SOC: P. Salucci, E. Aprile, P. Biermann, A. Bosma, A. Burkert, L. Danese, E. de Blok, C. Frenk, K. Freeman, R. Gavazzi, G. Gilmore, U. Klein, G. Mamon, C. Maraston, V. Rubin, P. Salati
OC: C. Frigerio Martins, G. Gentile, A. Lapi, S. Leach, C. Tonini
Overview
The concept of Dark Matter
Dark Matter in Spirals
Dark Matter in Ellipticals
Dark Matter in dSph
Direct and Indirect Method to detect Dark Matter
What is Dark Matter?
The mass profile of the gravitating matter M(r) and that of the sum of all luminous components ML(r) do not match.
A DARK MATTER COMPONENT is introduced to account for the disagreement:
Its profile MH(r) must obey to:
The DM phenomenon can be investigated only if we accurately meausure the distribution of: luminous matter. gravitating matter.
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
The distribution of the luminous matter
Spiral : stellar disk +bulge +HI disk
Ellipticals & dSph: stellar spheroid
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
flattish radial distribution
saturates at ~ 8 - 10 Msun pc-2 (NHI = 1021 cm-2)
deficiency in centre
CO or H2 surface density
roughly exponential
Wong & Blitz (2002)
HI surface density
ROTATION CURVE Symmetric circular rotation of a disk characterized by
sky coordinates (η0 ,ξ0 ) of the centre
• systemic velocity Vsys
• circular velocity V(R)
• position angle χ of the major axis
• inclination angle i
.
=bai arccos
iRVVV sysobs sincos)(),( θηξ +=i = inclination angle (0º = face-on)
θ = azimuthal angle
Vobs (R)= V(R) from spectroscopy:
- optical emission lines (Hα)
- 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
Hα, … 0.5" … 1.5" 10 … 30 km s-1
Optical & HI rotation curves
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0
50
100
150
200
250
V
R/Rd
UGC2405
The mass distribution is luminosity dependent. Gravitating matter is related with luminosity.
Tully Fisher exists at local level (radii Ri)
Very inner regions: light traces the mass
No DM there
DISK ONLY
Dark matter in galaxies
Bosma, 1978, 1981 First evidence!
GALEX
SDSS
Extended HI traces dark matterNGC 5055 on same scale:- HI velocity field - SDSS optical image - H-alpha velocity field- deep optical image - GALEX UV image
The Rotation Curves
coadded
PSS
6 RD
mag.
An Universal Mass Distribution?ΛCDM Universal Rotation Curve from NFW profile and MMW theory
The Concept of the Universal Rotation Curve
The Cosmic Variance of the value of V(x,L) in galaxies of (same) luminosity L @ the (same) radius x=R/RD is negligible with respect to the variations that V(x,L) show as x and L varies.
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, Moore) MASS MODEL HAS 2-3 FREE PARAMETERS: disk mass, halo
central density and core radius.
Vtot2 = VDM
2 + Vdisk2 + Vgas
2
Vdisk2
Vgas2
VDM2
EMPIRICAL distribution: Burkert profile
“cuspy” and “cored” density profiles of DM halos
”cusp”
”core”
Modelling the Universal Rotation Curve
Stars
Dark matter
DM
fr
actio
n
core radiushalo central density
luminosity
@Ropt
Stellar vs. Virial Halo Mass
Method: Shankar et al 2006.
The Universal Velocity Curve
URCL
NFW
URCH
Dark Halo Scaling Laws relationships between halo structural quantities (ρo, rc, σ) and luminosity
Kormendy & Freeman (2003) method- Assumed Maximun Disk-The slope of the halo rotation curve near the center gives the halo coredensity ρo
- extended RC provide an estimate of halo core radius rc
ρo ~ LB- 0.35
rc ~ LB 0.37
σ ~ LB 0.20ρo
rc
σ
the surface density Σ ~ ρo rc to be ~ constant
Kormendy & Freeman 2003
3.0 2.5
2.0
1.5
1.0
INDIVIDUAL OBJECTS
For every galaxy produce models with Υ* fixed to predicted value and with Υ* free
M/L* = 0.56
M/L* = 0.60
M/L* = 0.47
M/L* = 0.56
NGC3621: example of mass modeling
• THINGS: HI survey providing data of uniform and high quality
• multi-λ repository: powerful combination with UV and IR data
• high-quality rotation curves:• no declining curves• non-circular motions small• no DM halo elongation• ISO halos preferred over
NFW for low-mass galaxies
• tri-axiality and non-circular motions or “feedback” cannot explain the CDM cusp/core discrepancy
www.mpia.de/THINGS
DDO 47:
s1 negligible
s3 < 3 km s-1
ELLIPTICALS
Intensity distribution of bulges follows de Vaucouleurs (1948) law
or, its generalized form, a Sersic law
where Re is the effective radius, implying that one-half of the total light is emitted interior to Re.
Intensity distribution of a spheroid needs to be deprojected (Binney & Tremaine 1987; Binney & Merrifield 1998):
( )[ ]167.7 41
)( −−⋅= eRRe eIRI
The bulge
( )[ ]11
)( −−⋅=n
en RRbe eIRI
∫∫+ ∞+ ∞
∞− −==
R RrdrrrjdzrjRI
22
)(2)()(observer
Gary Mamon (IAP , Paris), for Dark Matter Awareness Week
Line-of-sight Velocity Dispersions
The Fundamental Plane in 4 bands
Bernardi et al. 2003
SDSS early-type galaxies
Fitting r ~ σa Ib yields (a<2, b~0.8) → M/L not constant
M/L ~ L0.14
The virial theorem (2KE=-W):
The FP “tilt” due to variations in: 1. dark matter fraction? 2. stellar population?
!! Stellar Mass FP!! M/L = (M/M*) (M*/L)Hyde & Bernardi 2009Now a<2 means M/M* not constant
>>> differences in fitting techniques >>> account for evolution + selection effects!
~ M*
Older galaxies have smaller M/M*
Shankar & Bernardi 2009
Mdyn(Re)=M*/2
Gary Mamon (IAP , Paris), for Dark Matter Awareness Week
Stars dominate inside few Re
Mamon & Łokas 05b
Mass decomposition
4 components:DMstarsBlack Holesgas
Gary Mamon (IAP , Paris), for Dark Matter Awareness Week
NGC 3379
dark matter content @ 4 Re still very uncertain!
The stellar mass of galaxies
The luminous matter in a galaxy in form of stars M* is a crucial quantity.Indispensable to infer the amount of Dark Matter Two contributions: - stars that are still alive- dead stellar remnants i.e. white dwarfs, neutron stars, black-holes
Luminosity of a galaxy is modeled via Stellar Population Synthesis models that determine its age and metallicity → M*/L, hence M*
Two methods: t and Z/H are obtained using line indices or colours. The correspondent M*/L (t, Z/H) gives M* the whole photometric SED is fitted and M* is obtained via normalization
Models for the evolution of the stellar mass
The M*/L ratio as a function of age
Maraston, Daddi + 06
SED fit:
M* crucially depends on how well we determine the galaxy star formation history
Mass Profiles from X Rays
Temperature
Density
Hydrostatic Equilibrium
M/L profile
Global dark matter fractionsVirial M/L can be rephrased as star formation efficiency εSF ≡ M* / (fb Mvir),
U-shaped curve observed:• “directly” with weak-lensing,• indirectly by correlating dN/dL with theoretical DM halo dN/dM
early-typelate-type
(fr. van den Bosch et al.)
(Mandelbaum et al. 2006)
εSF maximum near L*:• lower mass galaxies can’t hold gas• higher mass galaxies can’t cool gas
(Dekel & Silk 1986; Cattaneo et al. 2006)
Dark matter trends with galaxy luminosity
~ Reff : DM fraction(Tortora et al. 2009)
Increasing DM content with luminosity/mass: → decreasing star formation efficiency (feedback and/or inefficient cooling)
Detailed DM profiles with radius probe:→ alternative gravity / dark matter→ galaxy formation physics
~5 Reff : M/L gradient(Napolitano et al. 2005)
~ Rvirf weak lensing M/L(Mandelbaum et al. 2006)
WEAK LENSING
Weak Lensing around galaxies
Basic quantities are:
-) Lensing potential
-) The convergence k,that satisfies Poisson equation
and is directly related to the surface mass density
via the critical surface density
Tangential alignment of faint background sources (green ticks) in annuli around massive galaxies.
Gavazzi et al. 2007
Isothermal profile from ~Re/2 out to ~50Re
Bulge/halo «Conspiracy»: combine themselves to form an Isothermal r-2 profile although none of them is isothermal
Mandelbaum et al. 2006
Hoekstra et al. 2005
CFHT data (z~0.4)Scaling with luminosity M ~ Lα .
SDSS data (z~0.1). HOD framework: central/satellite distinction!!
Halo central density vs core radius
ρ0 =10-23 (r0 /kpc)-1 g/cm3 (WDM? De Vega et al 2010)
dSph
BURC
WL
The quantity ρ0r0 = Σ0 is constant among galaxies
census of HI masses: HI Parkes All Sky Survey (HIPASS)
Zwaan et al. (2005)
4315 HI detections
-1200 km s-1 < Vrad < 12700 km s-1
no ‘dark galaxies’
best fit: Schechter function
cosmological density of HI in local universe:
ΩHI = (3.5 ± 0.4 ± 0.4) ·10-4 h75
Zwaan et al. (2005)
−⋅
=Θ *
HI
HI*HI
HI*HI
HIHIHI M
MMMexp
MMM)(M dd
α