Difference between revisions of "Background on 20 GHz channel"

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= Background =
 
= Background =
  
During the CDT studies, we noticed a bias on r for one of the foreground models for the configuration under study at the time. The configuration was not designated with an official data challenge number. It can either be thought of as the configuration obtained from configuration 02 by rescaling by a factor sqrt(7/6), or equivalently as configuration 04 but with a 20 GHz channel on the SATs rather than the delensing LAT. For completeness, here is the performance table
+
During the CDT studies, we noticed a bias on r for one of the foreground models for the configuration under study at the time. The configuration was not designated with an official data challenge number. It can either be thought of as the configuration obtained from configuration 02 by rescaling by a factor sqrt(7/6), or equivalently as configuration 04 but with a 20 GHz channel on the SATs rather than the delensing LAT. For completeness, here is the performance table for the 4-year survey
  
 
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{| class="wikitable" style="text-align: right; margin-left: 51px;"
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The foreground model that displayed the bias was model 06, which is based on MHD simulations of the ISM.
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The foreground model that first displayed the bias was model 06, which is based on MHD simulations of the ISM.
  
 
Closer inspection of the ILC results revealed that the bias was caused by synchrotron residuals in bins 4-6. This can be seen in the figure below. The blue points and error bars indicate the ILC spectrum, green data points show the dust residuals, red data points show the synchrotron residuals.  
 
Closer inspection of the ILC results revealed that the bias was caused by synchrotron residuals in bins 4-6. This can be seen in the figure below. The blue points and error bars indicate the ILC spectrum, green data points show the dust residuals, red data points show the synchrotron residuals.  
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[[File:11.06_ILC.png|600px]]
 
[[File:11.06_ILC.png|600px]]
  
Comparison the noise power to power in synchrotron radiation, it is natural to suspect that this is caused by the large beam at low frequencies
+
The bias was subsequently confirmed with a second foreground model, also based on MHD simulations, with a somewhat different model of synchrotron emission.
  
[[File:Cl_Nl_20GHz.png|400px]]
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A comparison of the noise and synchrotron power spectra suggests that this is caused by the large beam at low frequencies and the associated drop in the signal-to-noise ratio on the synchrotron template
  
This motivated a study of the bias as a function of beam size at low frequency. A number of configurations were studied. I will show the most relevant subset, and refer to the configurations by my internal configuration numbers.
+
[[File:Cl_Nl_20GHz.png|523px]]
 +
 
 +
The analogous plots for the higher frequency channels show that the increase in resolution at 40 GHz at the noise levels considered is insufficient to compensate for the rapid drop of synchrotron emission with frequency. This motivated a study of the bias as a function of beam size at low frequency.  
 +
 
 +
A number of configurations were studied. I will show what I consider the most relevant subset, and refer to the configurations by my internal configuration numbers. The above numbers correspond to configuration 11. At 20 GHz lknee was taken to be 200 throughout.
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{| class="wikitable" style="text-align: right; margin-left: 51px;"
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! Beam FWHM @        !! 20 GHz !! 30 GHz !!  40 GHz
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|-
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| Configuration 11  || 76.6  || 76.6  ||  57.5
 +
|-
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| Configuration 13  || 15.0  || 76.6  ||  57.5
 +
|-
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| Configuration 16  || 30.0  || 76.6  ||  57.5
 +
|-
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| Configuration 17  || 45.0  || 76.6  ||  57.5
 +
|-
 +
| Configuration 18  || 60.0  || 76.6  ||  57.5
 +
|-
 +
| Configuration 19  || 11.0  || 76.6  ||  57.5
 +
|}

Revision as of 15:13, 6 June 2020

This posting summarizes the analyses that led to the decision to move the 20 GHz channel from the SATs to the delensing LAT.

Background

During the CDT studies, we noticed a bias on r for one of the foreground models for the configuration under study at the time. The configuration was not designated with an official data challenge number. It can either be thought of as the configuration obtained from configuration 02 by rescaling by a factor sqrt(7/6), or equivalently as configuration 04 but with a 20 GHz channel on the SATs rather than the delensing LAT. For completeness, here is the performance table for the 4-year survey

Frequency (GHz) 20 30 40 85 95 145 155 220 270
Beam FWHM (arcmin) 76.6 76.6 57.5 27.0 24.2 15.9 14.8 10.7 8.5
white noise level TT (uK-arcmin) 16.66 10.62 10.07 2.01 1.59 4.53 4.53 11.61 15.84
ell knee TT 500 175 175 175 175 230 230 230 230
1/f exponent TT -4.1 -4.1 -4.1 -4.1 -4.1 -3.8 -3.8 -3.8 -3.8
white noise level EE (uK-arcmin) 13.94 8.88 8.42 1.67 1.32 2.12 2.12 5.43 7.42
ell knee EE 200 50 50 50 50 65 65 65 65
1/f exponent EE -2.0 -2.0 -2.0 -2.0 -2.0 -3.0 -3.0 -3.0 -3.0
white noise level BB (uK-arcmin) 13.6 8.67 8.22 1.64 1.30 2.03 2.03 5.19 7.08
ell knee BB 200 50 50 50 50 60 60 60 60
1/f exponent BB -2.0 -2.0 -2.0 -2.0 -2.0 -3.0 -3.0 -3.0 -3.0
ell min 30 30 30 30 30 30 30 30 30
nside 512 512 512 512 512 512 512 512 512

The foreground model that first displayed the bias was model 06, which is based on MHD simulations of the ISM.

Closer inspection of the ILC results revealed that the bias was caused by synchrotron residuals in bins 4-6. This can be seen in the figure below. The blue points and error bars indicate the ILC spectrum, green data points show the dust residuals, red data points show the synchrotron residuals.

11.06 ILC.png

The bias was subsequently confirmed with a second foreground model, also based on MHD simulations, with a somewhat different model of synchrotron emission.

A comparison of the noise and synchrotron power spectra suggests that this is caused by the large beam at low frequencies and the associated drop in the signal-to-noise ratio on the synchrotron template

Cl Nl 20GHz.png

The analogous plots for the higher frequency channels show that the increase in resolution at 40 GHz at the noise levels considered is insufficient to compensate for the rapid drop of synchrotron emission with frequency. This motivated a study of the bias as a function of beam size at low frequency.

A number of configurations were studied. I will show what I consider the most relevant subset, and refer to the configurations by my internal configuration numbers. The above numbers correspond to configuration 11. At 20 GHz lknee was taken to be 200 throughout.

Beam FWHM @ 20 GHz 30 GHz 40 GHz
Configuration 11 76.6 76.6 57.5
Configuration 13 15.0 76.6 57.5
Configuration 16 30.0 76.6 57.5
Configuration 17 45.0 76.6 57.5
Configuration 18 60.0 76.6 57.5
Configuration 19 11.0 76.6 57.5