SLAC-2017:FSM Small angular scales

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Foregrounds, Systematics and Modeling: Small Angular Scales

Post session talks here.

Questions To be addressed for each small-scale science ‘probe’ (TT/TE/EE, lensing, tSZ/kSZ) towards defining measurement requirements - to start discussion/for context

How large do the large telescopes need to be? (NB - size of telescope is not a measurement requirement, but it is a simple proxy for resolution that varies with frequency in a realistic way)

  • Current status: studies indicate 5m (1.8' at 150 GHz) is sufficient for lensing (mnu and delensing) and high-ell TE/EE science (Neff), but may not be enough for cluster-derived science. Extra resolution doesn’t seem needed for cleaning TE/EE and lensing.
  • To-do: push forward cluster forecasts (see lunchtime discussion).
  • To-do: Baryonic physics of clusters is interesting -- can we define a good science metric?
  • To-do: Beam/other systematics -- plan to do more sophisticated treatment.

How many/which wavelengths do we need in the large telescopes?

(1) for TE/EE 2-pt for Neff

  • Current status: indicates that three is sufficient, based on new power spectrum simulations.
  • To-do: check impact of Galactic contamination

(2) for lensing (mnu/delensing) to avoid EB lensing bias

  • Current status: determining whether only 90/150/220 needed: work underway to test effect on lensing of expected non-Gaussian dust foregrounds. Might need synchrotron channels.
  • To-do: continue this work, test other sims. Compute delensing effect for various sims. Does delensing or mnu drive requirements?
  • Can look at real stage-3 data to avoid modelling uncertainies.

(3) for tSZ/kSZ (mnu/w/patchy-tau/growth/feedback)

  • Current status: at least 90, 150, 220 for tSZ. Suspect 270 GHz will be beneficial but assess expected noise levels. More frequencies would help separate kSZ, especially in power spectrum for reionization.
  • To-do: run cluster forecasts (for counts, tSZ power spectrum, y-maps, kSZ signal) on extragalactic sims

What are our systematic requirements for the 2pt and 4pt functions?

Can we achieve science requirements given realistic atmospheric noise?

  • Current status: realistic atmospheric noise consistent with Chilean observations without HWP has now been modeled and included in fisher forecasts for high-ell and lensing science. Neff/mnu parameters are not degraded.
  • To-do: include multi-freq realistic atmospheric noise in tSZ/kSZ forecasts, include South Pole noise curves. Establish agreement on atmospheric noise model being used by everyone.

Some people who have things to say on these topics:

  • Matthew Hasselfield - atmospheric noise model for large telescopes

Neff (TE/EE)-Discussion of Systematics and Foregrounds

  • Dan Green - Overview + Beams/Pointing - slides


  • Alex van Engelen - Impact of polarized dust on lensing
  • Mat M. / Colin H. - Multigrequency cleaning and extra spatial filtering
  • Yuuki Omori - Biases from extragalatic sources in temperature lensing


  • Marcelo Alvarez - extragalactic sims
  • Kevin Huffenberger (remote, 5 min) - Foregrounds and Atm noise for tSZ science slides
  • Simone Ferraro - foregrounds for kSZ slides
  • Lindsey Bleem - more on sims slides

Notes from session


  • Most info is from TE, l ~ 2000 - 4000
  • Beam effect: taking beam error as a single parameter on its width: sigma(10^-2) arcmin^2 to get sigma(Neff) < .03
    • Question: What is the best way to model the beam uncertainties -- if low-order polynomials, need uncertinties on each one
  • CIB / radio -- adding noise in TE
    • How well can this be cleaned with multi-frequency
    • Will finding sources to reduce the power from Poisson sources drive resolution requirements?


  • Dust models - Alex showed ongoing work characterizing bias. Also plan for computing delensing bias. Both come from <EBEB>
  • What measurement requirements are more stringent -- Lensing auto or delensing?
  • What frequency, angular resolution, and sky area do we need?
  • Discussion of map-level simulation analysis. To what extent do we need to do this for high-ell targets?


  • Baryonic physics of clusters is interesting -- can we define a good science metric?

Action items/Next steps

Summarize action items here