View source for SLAC-2017:FSM Small angular scales

Back to [[SLAC-2017:_Cosmology_with_CMB-S4| SLAC-2017 main page]]
==  Foregrounds, Systematics and Modeling: Small Angular Scales ==
Post session talks here.

*Neff discussion [[Media:Green_Neff_SLAC.pdf|slides]]
*Lensing discussion [[Media:Lensing_allslides.pdf|slides]]
*Clusters discussion [[Media:Clusters_allslides.pdf|slides]]
*Atmosphere [[Media:S4_noise_model_170228.pdf|slides]]

'''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 - [[Media:Green_Neff_SLAC.pdf|slides]]
 
''Lensing-related''

* 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

''Cluster-related''
* Marcelo Alvarez - extragalactic sims
* Kevin Huffenberger (remote, 5 min) - Foregrounds and Atm noise for tSZ science [[Media:huffenberger_src_atm_sz.pdf|slides]]
* Simone Ferraro - foregrounds for kSZ [[Media:Foregrounds_ferraro.pdf | slides]]
* Lindsey Bleem - more on sims [[:File:Bleem_small_scale_session_clusters.pdf |slides]]

== Notes from session ==

=== Neff ===

*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?

=== Lensing ===

* 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?

=== Clusters ===

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

== Action items/Next steps ==

Summarize action items here