Transcript PowerPoint Presentation - Extragalactic Foreground Sources…and

Extragalactic Foreground
Sources…and You!
Benjamin Recchie
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.
The COBE map of the universe.
Angular power spectrum of the CMB
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.
What we’re 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.
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
Galactic Foreground Sources
(and why I’m ignoring them)
• Galactic foregrounds contribute minimally for frequencies
from 10 to 100+ GHz.
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.
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.
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.
SZE Contribution to CMB
Measurements
Not much, up to high angular scales (l > 1000).
Extragalactic Radio Sources
• These consist primarily of Active Galactic
Nuclei (AGN). This includes:
–
–
–
–
–
radiogalaxies
QSOs
blazars
BL Lac objects
GHz Peaked Sources (GPS)
Extragalactic Radio Sources (cont’d)
• Up to 200 GHz, radio sources dominate the
errors; higher than that, dusty galaxies
dominate.
• However, not terribly important while l <
700 or so.
• Even non-radio galaxies still emit
microwave radiation.
• MAP and Planck probably won’t have
interference from extragalactic radio
sources.
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).
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.
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.
The Future:
MAP
• 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:
The Future:
Planck
• 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 highfrequency extragalactic microwave sources.
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.