Subpixel HFI

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 N_side=128) CO simulated map and the input full resolution (at N_side=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) and given in PLA (LVLV).

For convenience, we also provide (b) the maps of the logarithm of the ratio of the bias variance, in each N_side=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. Those ratio maps are also provided in the PLA (LVLV).

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 % the rms of the bias at N_side=2048 inside the pixel at N_side=128 referred to the rms of the noise at N_side=2048 inside the same pixel at N_side=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, Galactic science work with the HFI data in these very bright regions should be done with the specifically built maps from HPRs (LVLV) at the full resolution.

CO templates

	100 GHz			143 GHz	217 GHz			353 GHz
	I	Q	U	.	I	Q	U	I	Q	U
(a): frequency averaged bias maps [μK]				.
(b): bias noise ratio maps [math] \log_{10} \left(\frac{\textrm{bias map}}{\textrm{noise map}}\right)[/math]				.
(c): [math] \log_{10} \left(\frac{\textrm{bias map}}{\textrm{full intensity map}}\right)[/math]				.
100%	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 %