Extragalactic Foreground SourcesÉand You! |
Benjamin Recchie | |
The Cosmic Microwave Background |
Cosmic Microwave Background (CMB) is an ÒechoÓ 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. |
But Reality (and the Foreground) Intervenes... |
The sky is cluttered in all directions with galaxies and other extragalactic objects which contribute microwave ÒnoiseÓ that obscures the CMB. |
What weÕre 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 IÕm 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 |
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 (contÕd) |
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 wonÕt 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. |
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 high-frequency 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. |