From CMB-S4 wiki
Jump to navigationJump to search
Revision as of 09:00, 20 September 2015 by Dunkley (→What simulations and tools do we have for forecasting impact on r? (detailed discussion on Tues))
- 1 Foregrounds
- 1.1 What are our latest estimates of foreground levels post-Planck?
- 1.2 What simulations and tools do we have for forecasting impact on r? (detailed discussion on Tues)
- 1.3 What are still physical unknowns?
- 1.4 Do we need new data at <40 GHz and >230-300 GHz? And what about 60GHz?
- 1.5 How important is large sky area?
- 1.6 What is the path to a convincing claim that a B-mode signal is not foregrounds?
What are our latest estimates of foreground levels post-Planck?
- Figure from Steve Choi/Lyman Page:
- John Ruhl: Can we make a new version of this figure (Steve could make input, who made it originally?):
What simulations and tools do we have for forecasting impact on r? (detailed discussion on Tues)
Jacques, Raphael, Stephen F, Aurelien, Brendan, Jo...
- Raphael: Does a new PSM exist right now that we could use? http://www.apc.univ-paris7.fr/~delabrou/PSM/psm.html. Common sim maps would be great.
- 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]. They have 3 figures of merit.
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.
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:
- 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?
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.
What is the path to a convincing claim that a B-mode signal is not foregrounds?
- Nulls between frequencies, areas, scales