Extragalactic Foreground Sources

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Extragalactic Foreground Sourcesand You!

• Benjamin Recchie

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The Cosmic Microwave Background

• Cosmic Microwave Background (CMB) is an echo of
  the Big Bang.
• Small anisotropies (less than 1 part in 100000)
  in CMB can be analyzed to learn about very early
  universe.
• In theory, we can just point our radio telescopes
  at the sky and measure the CMB.

Angular power spectrum of the CMB
The COBE map of the universe.
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But Reality (and the Foreground) Intervenes...

• The sky is cluttered in all directions with
  galaxies and other extragalactic objects which
  contribute microwave noise that obscures the
  CMB.

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What were trying to do

• We can improve our knowledge of the CMB if we can
  only get rid of (or find some way to ignore)
  these pesky foregrounds sources.

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Summary of Foreground Sources

• Sunyaev-Zeldovich Effect
• Thermal SZE -creates slightly shifted blackbody
  spectrum.
• Kinetic SZE - creates blackbody spectrum at
  slightly different temperature.
• Extragalactic Radio Sources
• Active Galactic Nuclei, QSOs, etc.
• Far-Infrared Sources
• IR sources contribute considerable microwave
  radiation
• Various and Sundry Galactic Sources
• Free-free radiation, galactic dust, synchrotron
  radiation

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Galactic Foreground Sources(and why Im ignoring
them)

• Galactic foregrounds contribute minimally for
  frequencies from 10 to 100 GHz.

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The Sunyaev-Zeldovich Effect

• The Sunyaev-Zeldovich Effect (SZE) arises from
  gas heated (mainly) by falling into a
  gravitational well.
• Leads to distortion of the blackbody spectrum for
  CMB photons.
• Can be used to independently verify cosmological
  parameters.

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Thermal Sunyaev-Zeldovich Effect

• CMB photons undergo Compton scattering from
  electrons in heated gas, and gain some energy.
• Shifts CMB spectrum up in energy.
• Larger than kinetic effect by at least a factor
  of ten at most frequencies.
• Relatively easy to account for and correct.

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Kinetic Sunyaev-Zeldovich Effect

• Moving gas creates false appearance of blackbody
  at different temperature from microwave
  background.
• Has same spectral behavior as CMB anisotropy.
• Difficult to correct for, but relatively minor.

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SZE Contribution to CMB Measurements
Not much, up to high angular scales (l gt 1000).
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Extragalactic Radio Sources

• These consist primarily of Active Galactic Nuclei
  (AGN). This includes
• radiogalaxies
• QSOs
• blazars
• BL Lac objects
• GHz Peaked Sources (GPS)

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Extragalactic Radio Sources (contd)

• Up to 200 GHz, radio sources dominate the errors
  higher than that, dusty galaxies dominate.
• However, not terribly important while l lt 700 or
  so.
• Even non-radio galaxies still emit microwave
  radiation.
• MAP and Planck probably wont have interference
  from extragalactic radio sources.

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Far-Infrared Sources

• Far-IR sources emit considerable radiation in the
  microwave.
• Many galaxies emit most of their radiation in IR
  and sub-millimeter wavelengths.
• Dust absorbs UV and optical wavelength light and
  reradiates it in the far-infrared.
• Side note there also exists a Cosmic Infrared
  Background (CIRB).

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LIRGs and ULIRGs

• Nearby LIRGs and ULIRGs are merging or otherwise
  interacting presumably, most such galaxies are
  the same.
• Hubble Deep Field image shows many objects
  undergoing gravitational interactions.

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But do they matter for CMB studies?

• Models predict Planck will detect thousand of IR
  sources at after filtering.
• For example - at 857 GHz, 40000 sources
  predicted at 545 GHz, 5000 sources.
• However, models also predict virtually no far-IR
  sources around prime frequencies for CMB
  measurements.

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The FutureMAP

• MAP will observe background from 22 to 90 GHz,
  with angular resolution of 0.3 degrees.
• Will measure galactic foreground more precisely,
  so that it can be subtracted from other studies.

MAP will turn this
to this
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The FuturePlanck

• Planck will observe background from 50 to 850
  GHz, with resolutions of 5 to 10 arcminutes,
  depending on the instrument.
• Will be able to observe certain high-frequency
  extragalactic microwave sources.

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Conclusions

• The thermal Sunyaev-Zeldovich effect has major
  effect on the CMB spectrum at large angular
  scales, but is easy to correct for. The kinetic
  Sunyaev-Zeldovich effect is much harder to
  correct for, but is very small.
• Extragalactic radio sources make small but
  ultimately unimportant contributions to CMB up
  through large angular scales (but are interesting
  in and of themselves).
• Far-infrared sources deserve more study, but will
  also probably require only minor corrections to
  newer measurements of the CMB.
• Planck and MAP will answer many of our questions
  about the CMB, and should be able to bypass most
  foreground sources.