Projected-field kSZ

CLASS_SZ

Velocity Reconstruction

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Boris Bolliet

DAMTP, Cambridge

with many colleagues from ACT/SO

CMB-S4 Collaboration Meeting

April 3-6, 2023

Projected-field kSZ - what is it?

• An estimator/A way to extract the small-scale kSZ effect

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Slide 2

• 2-point small-scale kSZ is challenging to probe until >=SO (see Srini)

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• Today possible in cross-correlations, but have to deal with velocity cancellation at small-scale

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• Idea: square+filter CMB map and take the cross with LSS�
• Complementary to stacking/”TTg” type analyses (Schaan, Amodeo+)�
• Naturally works with CMB and galaxy lensing too

Boris Bolliet

CMB-S4 Collaboration Meeting, April 3-6, 2023

Projected-field kSZ - the estimator

Slide 3

where X is the LSS tracer�B is the electron-electron-LSS bispectrum

• Several methods to predict analytically (Dore, Spergel, Hill, Ferraro)�
• One of them is the halo-model (Bolliet+)�
• With halo-model we can access/probe info in intra-cluster-medium�gas density

Boris Bolliet

CMB-S4 Collaboration Meeting, April 3-6, 2023

Projected-field kSZ - measurements

Slide 4

• 1st measurement Hill et al 2016 using Planck and WISE�
• 2nd measurement Kusiak et al 2021 using Planck and unWISE - constraints on baryon fraction

• Challenges: need CIB/dust-free map and a well characterized galaxy samples

Boris Bolliet

CMB-S4 Collaboration Meeting, April 3-6, 2023

Projected-field kSZ - forecasts

Slide 5

• Projected-field kSZ will be a key observable to characterize the distribution of baryons around halos used in cosmological analysis. Useful for S8-tension. �
• Needed now: develop pipeline for applications to realistic simulations (e.g., Lau, Osato, Li, Nagai, Omori,+)

• See https://arxiv.org/pdf/2208.07847.pdf

Boris Bolliet

CMB-S4 Collaboration Meeting, April 3-6, 2023

How to compute such observables? FFTLog + emulators

Slide 6

• Class_sz : https://github.com/CLASS-SZ/class_sz�
• Tutorial notebooks: https://github.com/CLASS-SZ/notebooks�
• Code already public, official (re-)release imminent (with Kusiak, McCarthy, Sabyr, Surrao, Hill+)

Boris Bolliet

E.g. includes Maniyar CIB,

Schneider et al BCM model, etc

• Real space correlations�+ accelerated cluster-counts likelihood�(Zubeldia & Bolliet, in prep.)

Battaglia+ density profile

Integrand of tSZ spectrum

CMB-S4 Collaboration Meeting, April 3-6, 2023

CLASS_SZ high-accuracy emulators wrapper

Slide 7

• New high-accuracy emulators based on cosmopower (Spurio-Mancini et al, see https://arxiv.org/pdf/2303.01591.pdf)

• Can run Mcmcs in few minutes with S4-level accuracy. Works with DESY3, BAOs, Lensing+�
• Example:

https://github.com/CLASS-SZ/notebooks/blob/main/mcmcs/cobaya/notebooks/planck_HMTTTEEE_lite_native.ipynb

Boris Bolliet

CMB-S4 Collaboration Meeting, April 3-6, 2023

Velocity reconstruction

Slide 8

• See Cayuso et al https://arxiv.org/abs/2111.11526 (plot below)�
• Key idea: use small scale statistical anisotropy of “Tg”, to reconstruct the large scale modes of velocity field�
• Current ongoing analyses: upper bound from Planck x unWISE (Johnson+)

• Challenges: astrophysics degeneracies and�Foregrounds.��
• But promises are extremely motivating: �E.g., primordial non-Gaussianity (see Munchmeyer+ https://arxiv.org/pdf/2111.11526.pd) �
• sigma_fNL = 0.5 with LSST x S4 (3x LSST alone, e.g. Omar)

Boris Bolliet

CMB-S4 Collaboration Meeting, April 3-6, 2023

Conclusion

• Projected-field kSZ a (relatively) novel probe that will enable to constrain ICM density�Important for WL analysis (S8 tension), and galaxy formation science. ��
• New S4-level accuracy emulators for CMB and Pk available and wrapped within the new CLASS_SZ code (https://github.com/CLASS-SZ/class_sz)��
• Velocity reconstruction offers (maybe the most promising) way to probe high-energy physics (inflation) using electron scattering in the ICM (SZ effects). S4 can/will do it!

Slide 9

Boris Bolliet

CMB-S4 Collaboration Meeting, April 3-6, 2023