Very bright regions where the sub-pixel effect in the SRoll CO foreground templates prevent them to be used for cosmology or astrophysics analysis

From Planck Legacy Archive Wiki
Revision as of 11:18, 11 December 2017 by Lvibert (talk | contribs)
Jump to: navigation, search


editing in progress

The bandpass corrections have been optimized for high latitude regions which implied to reduce the noise of the CO and dust bandpass templates to avoid the introduction of significant correlated noise. The effect is negligible for dust but not for CO in bright regions. We simulated the effect to evaluate its level. The difference between the downgraded (at Nside=128) CO simulated map and the input full resolution (at Nside=2048) CO simulated map gives the simulated bias introduced by this downgrading for each bolometer. For each frequency channel, these bias maps are converted to HPRs, multiplied by the corresponding CO bandpass coefficients computed by SRoll using data, and projected onto a frequency map of the bias for the frequency. Those frequency averaged bias maps are displayed in the table (a).

For convenience, we also provide (b) the maps of the logarithm of the ratio of the bias variance, in each Nside=128 pixel, and the variance of the noise level estimated from the End-to-End simulations. The level of the bias is well determined and specific masks adapted to each scientific analysis can be computed at the appropriate level.

We also provide (c) the ratio of the variance bias maps to the variance of the full intensity signal.


The table also gives the sky fraction to be masked for thresholding the bias at 100, 10, and 1 % of the rms of the noise at Nside=2048 inside the pixel at Nside=128 referred to the rms of the noise at Nside=2048 inside the same pixel at Nside=128.

The effects are largest at 100 GHz. It can also be noted that, for polarization, only less than 10-3 of the sky is affected by this bias at the noise level. For intensity, the biais is an order of magnitude lower. If the user wants to reduce the bias below 10 % of the noise in polarization, 2% of the sky will be affected. Users can also refer to the absolute value of the bias with respect to the CO maps to build the relevant mask.

As recommended in Planck-2020-A3[1], Galactic science work with the HFI data in these very bright regions should then be done starting from the HPRs (see HERE) at the full resolution.


CO templates
link to PLA 100 GHz 143 GHz 217 GHz 353 GHz
I Q U . I Q U I Q U
(a): frequency averaged bias maps [μK] LVLV 100-I CO Subpix Val.png 100-Q CO Subpix Val.png 100-U CO Subpix Val.png . 217-I CO Subpix Val.png 217-Q CO Subpix Val.png 217-U CO Subpix Val.png 353-I CO Subpix Val.png 353-Q CO Subpix Val.png 353-U CO Subpix Val.png
(b): [math]\log_{10} \left(\frac{\lt \textrm{bias}\gt \textrm{map}}{\lt \textrm{noise}\gt \textrm{map}}\right)[/math] LVLV 100-I CO Subpix.png 100-Q CO Subpix.png 100-U CO Subpix.png . 217-I CO Subpix.png 217-Q CO Subpix.png 217-U CO Subpix.png 353-I CO Subpix.png 353-Q CO Subpix.png 353-U CO Subpix.png
(c): [math]\log_{10} \left(\frac{\lt \textrm{bias}\gt \textrm{map}}{\lt \textrm{full intensity}\gt \textrm{map}}\right)[/math] LVLV 100-I CO Subpix Val DIV Signal.png 100-Q CO Subpix Val DIV Signal.png 100-U CO Subpix Val DIV Signal.png . 217-I CO Subpix Val DIV Signal.png 217-Q CO Subpix Val DIV Signal.png 217-U CO Subpix Val DIV Signal.png 353-I CO Subpix Val DIV Signal.png 353-Q CO Subpix Val DIV Signal.png 353-U CO Subpix Val DIV Signal.png
sky fraction above 100% of (b) . 0.0000 % 0.0000 % 0.0005 % . 0.0000 % 0.0000 % 0.0000 % 0.0000 % 0.0000 % 0.0000 %
10% . 0.0112 % 0.0092 % 0.0346 % . 0.0000 % 0.0061 % 0.0056 % 0.0000 % 0.0000 % 0.0005 %
1% . 0.4186 % 0.7370 % 1.4318 % . 0.0270 % 0.1643 % 0.1094 % 0.0071 % 0.0361 % 0.0478 %

References[edit]

(Planck) High Frequency Instrument

Planck Legacy Archive