Constraining Galactic Halos with the SZ-effect

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Constraining Galactic Halos with the SZ-effect

• by Naureen Goheer,
• University of Cape Town
• based on a collaboration with
• Kavilan Moodley (UKZN)

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Galaxy morphology
spirals much better understood, focus on them
rich in gas and dust
90
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far less evidence for young stars, gas, or dust
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Optical part of Spiral Galaxies

• two visible components

lt 10 of visible mass Bulge (stars)
90 of the visible mass spiral arms (stars
gasdust)
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invisible matter component Halo
Stellar Halo, lt 1 of stars
visible part
Dark Matter Halo
some indirect observational evidence for the
existence of Halo
baryonic
non-baryonic
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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

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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

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CMB Anisotropies
Secondary Anisotropies effects due to structure
formation (nonlinear structure evolution)
gravitational effects (lensing) scattering
effects
SZ-effect scattering of CMB photons on hot gas
Primary Anisotropies early effects at the last
scattering surface and large scale Sachs-Wolfe
effect.
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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

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CMBblack body
distinct spectral signature
lower intensity at no effect at higher intensity
at
allows us to distinguish signal from other sources
scattering of CMB photons on e- in hot gas
net effect
photons pick up energy and get shifted to higher
frequencies
distortion of black body spectrum
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Thermal SZ-effect Central decrement
empirically number density of e- highest in the
center and falls off radially
central decrement
dl
frequency dependence
Comptonization parameter gas pressure along the
line of sight
thermal SZ depends on temperature and number of
electrons in gas
mass of object

• purely classical treatment
• must include relativistic effects when
• (e.g. in clusters)

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integrated effect (over entire object)

• high central decrement for clusters (higher
  temperature and mass)
• much smaller central decrement due to much lower
  mass and lower temperature in galaxies

integrate over angular size
dl

• 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

BUT
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other observational constraints

• spectroscopy can only test for specific isotopes
  using
• X-rays observe Bremstrahlung etc.

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SZ-effect versus X-rays

• X-ray luminosity
• SZ-flux

electron temperature
central electron density
for extended halos with low central density,
X-rays observations are less sensitive than
SZ-observations!
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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)

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discarded slides
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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

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Whats nice about SZE?

• 1) Ofcourse, the distinct spectral signature
• 2) Measures the total thermal content of the
  cluster
• 3) More or less redshift independent
• 4) Less susceptible to messy cluster
  substructure, core
• physics (prop to density and not density
  squared as in XRays)

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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.
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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 .
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CMB Anisotropies
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
Primary Anisotropies early effects at the last
scattering surface and large scale Sachs-Wolfe
effect.
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The SZ-effect

• Thermal Sunyaev-Zeldovich 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-Zeldovich 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.