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Extragalactic Foreground Sources

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Cosmic Microwave Background (CMB) is an 'echo' of the Big Bang. ... Has same spectral behavior as CMB anisotropy. Difficult to correct for, but relatively minor. ... – PowerPoint PPT presentation

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Title: Extragalactic Foreground Sources


1
Extragalactic Foreground Sourcesand You!
  • Benjamin Recchie

2
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.
3
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.

4
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.

5
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

6
Galactic Foreground Sources(and why Im ignoring
them)
  • Galactic foregrounds contribute minimally for
    frequencies from 10 to 100 GHz.

7
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.

8
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.

9
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.

10
SZE Contribution to CMB Measurements
Not much, up to high angular scales (l gt 1000).
11
Extragalactic Radio Sources
  • These consist primarily of Active Galactic Nuclei
    (AGN). This includes
  • radiogalaxies
  • QSOs
  • blazars
  • BL Lac objects
  • GHz Peaked Sources (GPS)

12
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.

13
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).

14
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.

15
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.

16
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
17
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.

18
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.
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