constraining galactic halos with the sz-effect
DESCRIPTION
Constraining Galactic Halos with the SZ-effect. by Naureen Goheer, University of Cape Town based on a collaboration with Kavilan Moodley (UKZN). Galaxy morphology. spirals much better understood, focus on them. rich in gas and dust. 90%. 10%. - PowerPoint PPT PresentationTRANSCRIPT
Constraining Galactic Halos with the SZ-effect
by Naureen Goheer, University of Cape Town
based on a collaboration with Kavilan Moodley (UKZN)
Galaxy morphology
galaxies
elliptic
spiral-unbarred
spiral-barred
10%
rich in gas and dust
far less evidence for young stars, gas, or dust
90%
kPc 001-5 :size
M1010 :mass sol119
kPc 001-1/10 :size
M1010 :mass sol137
spirals much better understood,focus on them
Optical part of Spiral Galaxies• two visible components
< 10% of visible mass: Bulge (stars)
~ 90 % of the visible mass:spiral arms (stars + gas&dust)
“invisible” matter component: Halo
Dark Matter Halo some indirect observational evidence for the existence of Halo
Stellar Halo, < 1% of stars
visible part
baryonic non-baryonic
DM Halo and Observations• some indirect observational evidence
for the existence of Halo through kinematic tracers, e.g:•disk galaxy rotation curves , •satellite galaxies and globular clusters, •hot gas (also around ellipticals) confirm existence of halo
• radial extents and total masses of these halos remains poorly constrained
• one possible new way of constraining amount of dark baryons is the SZ-effect
DM Halo and Theory
• might account for missing baryons (only 20% of mean baryonic density has been observed)
• DM halo required by most models of galaxy formation
• galaxy formation still not understood – have no accepted model of galaxy formation, thus no accepted halo model
• expect different halo dynamics depending on whether the galaxy at hand is starburst or quiescent; smooth halo or filaments
CMB Anisotropies
Primary Anisotropies: early effects at the last scattering surface and large scale Sachs-Wolfe effect.
Secondary Anisotropies –effects due to structure formation (nonlinear structure evolution) –gravitational effects (lensing)–scattering effects
SZ-effect: scattering of CMB photons on hot gas
The Sunyaev Zel'dovich (SZ) effect
• secondary anisotropies due to (up-)scattering of CMB photons with hot gas (keV) along the line of sight (at the centre of clusters etc.)
• thermal: due to the thermal velocities of the electrons in the gas
• kinematic: due to the bulk velocity of gaseous object
CMB=black body
scattering of CMB photons on e- in hot gas
distortion of black body spectrum
photons pick up energy and get shifted to higher frequencies
net effect
lower intensity at no effect athigher intensity at
GHz 210GHz 210
GHz 210
distinct spectral signature
allows us to distinguish signal from other sources
Thermal SZ-effect: Central decrement
Comptonization parameter=gas pressure along the line of sight
frequency dependence
dlnTT ee
thermal SZ depends on temperature and number of electrons in gas
empirically: number density of e- highest in the center and falls off radially
dlcentral decrement
• purely classical treatment • must include relativistic effects when (e.g. in clusters)
mass of object
keVTk eB 10
dlcm
TknTfT
e
eBTeCMB 2
)(
• high central decrement for clusters (higher temperature and mass)
• much smaller central decrement due to much lower mass and lower temperature in galaxies
dlnTT ee dlndTT ee integrated effect
(over entire object)
integrate over angular size
dld
BUT
• observable integrated effect (if halo is massive and hot enough)
• use integrated effect to constrain electron number density and thus the dark baryons in halo of nearby galaxies
• assuming that non-baryonic DM scales like dark baryons, this constrains the total DM content of halo
other observational constraints
• spectroscopy: can only test for specific isotopes using
• X-rays: observe Bremstrahlung etc.
SZ-effect versus X-rays
• X-ray luminosity:
• SZ-flux:
2/12)0( eex TnL
eeSZ TnS )0(
2/1
)0(
e
e
SZ
x
T
n
S
L
for extended halos with low central density, X-rays observations are less sensitive than SZ-observations!
electron temperature
central electron density
Summary and Future outlook
• 80% of the predicted baryons have not been observed• some of them might hide in the hot halos of galaxies• very difficult to directly measure the halo content
• the integrated thermal SZ-effect can be used to directly measure baryonic matter content of halo
• the new Atacama Telescope (ACT) will have high enough sensitivity to get a clear signal (better than PLANCK)
discarded slides
models of galaxy formation
• explain different halo scenarios: halos can be smooth or filled with filaments (mention models of galaxy formation)
• halo content: O VI (observed using x-rays, show example pics)
• what can we learn about models of galaxy formation
Whats nice about SZE?1) Ofcourse, the distinct spectral signature2) Measures the total thermal content of the cluster3) More or less redshift independent4) Less susceptible to messy cluster substructure, core physics (prop to density and not density squared as in XRays)
Note that at GHz, the maximum change in intensity due to the kinematic effect coincides with the null of the thermal effect.
This, in principle, allows one to separate the two effects. The magnitude of the thermal effect for a hot, dense cluster is , and for reasonable cluster velocities the kinematic effect is an order of magnitude smaller.
210
mK 1)( thermal RJT
OR
Primary Anisotropies :early effects at the last scattering surface and large scale Sachs-Wolfe effect.
Secondary Anisotropies:secondary contributions through nonlinear structure evolution, star formation, and radiative feedback from the small scales to the large .
CMB Anisotropies
Primary Anisotropies: early effects at the last scattering surface and large scale Sachs-Wolfe effect.
Secondary Anisotropies contributions through nonlinear structure evolution, star formation, and radiative feedback from the small scales to the large .
SZ-effect: scattering of CMB photons on hot gas
The SZ-effect• Thermal Sunyaev-Zel’dovich effect: Inverse
Compton scattering of the CMB by hot electrons in the intracluster gas of a cluster of galaxies distorts the black body spectrum of the CMB. Low frequency photons will be shifted to high frequencies.
• Kinetic Sunyaev-Zel’dovich effect: The peculiar velocities of clusters produces anisotropies via a Doppler effect to shift the temperature without distorting the spectral form. Its effect is proportional to the product of velocity and optical depth.