Effect of the Galactic plane on the COBE CMBR measurements

  • Thread starter Tanelorn
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  • #1


CMBR dipole anisotropyFrom the CMB data it is seen that our local group of galaxies (the galactic cluster that includes the Solar System's Milky Way Galaxy) appears to be moving at 627±22 km/s relative to the reference frame of the CMB (also called the CMB rest frame, or the frame of reference in which there is no motion through the CMB) in the direction of galactic longitude l = 276±3°, b = 30±3°.[60] This motion results in an anisotropy of the data (CMB appearing slightly warmer in the direction of movement than in the opposite direction).[61] The standard interpretation of this temperature variation is a simple velocity redshift and blueshift due to motion relative to the CMB, but alternative cosmological models can explain some fraction of the observed dipole temperature distribution in the CMB

I was trying to find out if our galaxy has a power spectrum which can also be considered a black body with a certain temperature?

Also regarding the CMBR black body radiation what is the radiation signal strength or spectral power density and what does this tell us?
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Answers and Replies

  • #3
Thanks Drakkith. What are MJy/sr and how do I convert to W/√Hz?

Answering my own question, I am guessing that the power spectrum of a galaxy is nothing like a black body. So the in band radiation is an interferer for the CMBR measurement.

How much radiation energy is out there from an infinite universe full of galaxies? Just wondering how much they all contribute to or interfere with the received CMBR radiation signal strength?
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  • #5
Thanks Drakkith, I learnt about Janskys today!
  • #6
So how much radiation energy is out there from an infinite universe full of galaxies? Just wondering how much they all contribute to, or interfere with, the received CMBR signal strength?

I understand that Cosmologists are trying to find tiny variations in the CMBR, but it occured to me that clusters and superclusters of galaxies could also be contributing to the received RF in a similar way to the way our galaxy interferes, as mentioned above. So I just wondered what are the estimated relative levels for the galactic radiation (RF), compared to the CMBR signal strength?

Also are there any other known mechanisms out there for producing RF interference with similar frequency to the CMBR?

CMBR Center Frequency:

Precise measurements of cosmic background radiation are critical to cosmology, since any proposed model of the universe must explain this radiation. The CMBR has a thermal black body spectrum at a temperature of 2.725 K, thus the spectrum peaks in the microwave range frequency of 160.2 GHz, corresponding to a 1.9 mm wavelength. This holds if measured per unit frequency, as in Planck's law. If measured instead per unit wavelength, using Wien's law, the peak will be at 1.06 mm corresponding to a frequency of 283 GHz.


Black Body Radiation:

A black body is an idealized physical body that absorbs all incident electromagnetic radiation. Because of this perfect absorptivity at all wavelengths, a black body is also the best possible emitter of thermal radiation, which it radiates incandescently in a characteristic, continuous spectrum that depends on the body's temperature.


So could the thinly spread matter between galaxies absorb radiation energy from galaxies and then emit radiation energy at the CMBR frequency like a black body described above?

Possible sources of CMBR interference: Emisson lines in the THz region:


"However, the CO transition at 115 GHz has been detected in FSC10214 and should be observable with an enhanced VLA in many sources":

"Using the waveguide-type sideband-separating SIS mixer for the 200 GHz band, we initiated the first simultaneous 12CO (J = 2 - 1) and 13CO (J = 2 - 1) survey of the galactic plane as well as large-scale mapping observations of nearby molecular clouds":

"Evidence that Synchrotron Emission from Nonthermal Electrons Produces the Increasing Submillimeter Spectral Component in Solar Flares":
We investigate the origin of the increasing spectra observed at submillimeter wavelengths detected in the flare on 2 November 2003 starting at 17:17 UT. This flare, classified as an X8.3 and 2B event, was simultaneously detected by RHESSI and the Solar Submillimeter Telescope (SST) at 212 and 405 GHz.
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  • #7
Are these questions useful?
  • #8
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Are these questions useful?

Sure. They just aren't easily answerable. I assume cosmologists or whoever that work with the CMB have to account for these variations, I just don't know how they do that.