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What are our latest estimates of foreground levels post-Planck?

Steve, Raphael...

  • Figure from Steve Choi/Lyman Page:


  • Figure from Stephen Feeney/Hiranya/Andrew Jaffe/Josquin:


  • John Ruhl: Can we make a new version of this figure (Steve could make input, who made it originally?):


  • Clem: We have not been able to exactly reproduce fig8 of PIPXXX. Here's a comparison:

Pipxxx fig 8.gifPipxxx fig 8 orig.png

What simulations and tools do we have for forecasting impact on r? (detailed discussion on Tues)

Jacques, Raphael, Stephen F, Aurelien, Brendan, Jo...

  • Aurelien: Addressing questions about model uncertainty requires a flexible simulation facility, which can be easily modified and run by everyone for a wide range of parameters, and interfaced with current analysis and forecasting pipelines. Ideally would use python and have mechanism for the community to contribute to development and easily make and share own simulations. PSM is great, but how do we make the best use of it as a starting point.
  • Brendan: had a problem using the PSM during the BKP analysis – the dust polarization model in the PSM comes from a filtered version of Planck 353, so includes Planck noise, and there is nowhere in the PSM sky that is as clean as dust as the real Bicep region
  • We still still want ability to do quick and dirty Fisher forecasts for exploring different set-ups, so still want quick ways to inflate Nl for example. There is a useful prescription in upcoming paper, Feeney, Errard, Peiris, Jaffe 2015, that includes foregrounds and delensing [still makes assumptions about FG of course].
  • Feeney: useful 3 figures of merit and some estimates of residual r:


Feeney resid.png

What are still physical unknowns?

Aurelien, Brandon Hensley, Bruce Draine, Al Kogut, Brendan

  • They include magnetic dust, spinning dust polarization, spatial dispersion of dust temperature/emissivity...
  • Brendan: At what point we think that the greybody model for dust emission will break down?
  • Aurelien: worried by the spatial variations of dust properties. Taking these into account in forecasts is difficult, since they represent a failure in our theoretical understanding. How do we get around this? Is there a way to cook up a strategy, in terms of frequency and spatial coverage, that would make our forecasts somewhat immune to these uncertainties?
  • Jo: Don't yet know enough from Planck: dispersion in dust index between individual 300 deg2 (i.e. large!) patches is about +-0.15 and varies between beta = 1.1 and 2.2.
  • Clem: Where does the above statement come from? Fig E.1 of PIP-XXX seems to show spatial/spectral variation of dust is pretty small.

Pipxxx fig e1.png

Do we need new data at <40 GHz and >230-300 GHz? And what about 60GHz?

Clem,John, Aurelien, Jo...

  • The effective polarized noise from cleaning 150 GHz with Planck 353 GHz is about 19 uK-arcmin, i.e. an additional sigma(r) ~0.01 for fsky=0.2
  • Al Kogut has done sims for PIXIE to look at possible residuals given varying dust temperature, showing that broader freq coverage is important
  • John: useful figure from BKP (updated):

Bkp fig13.png

  • Jo: pessimistic/realistic inflation of CMB errors using map-based cleaning if we loosen dust assumptions:


  • Aurelien: For 60 GHz, want something there in the long term to understand dust / synchrotron correlations. But in the medium term, how well can we do without it?
  • Clem: for given s/n it's better to constrain the dust at (e.g) 220 than 350GHz - the shorter the lever-arm the less the impact of spatial variation of the frequency spectrum.

How important is large sky area?

  • If we detect B-modes, more sky area will help with cosmic variance
  • Without foregrounds, fsky doesn't help you that much for a detection. But! required if we want detections from different regions of sky.
  • But if r is undetectably low, strongest upper limits come from small f_sky.
    • Is it clear which direction this optimization is pushed by foregrounds? Systematics?

What is the path to a convincing claim that a B-mode signal is not foregrounds?

  • Nulls between frequencies, areas, scales