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Component-separated, CIB-cleaned thermal Sunyaev--Zel'dovich maps from Planck PR4 data with a flexible public needlet ILC pipeline

3 Jul 2023arXiv:2307.01043links table onlyarchive 2025-07-28

Fiona McCarthy, J. Colin Hill

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We use the full-mission Planck PR4 data to construct maps of the thermal Sunyaev$--$Zel'dovich effect (Compton-y parameter) in our Universe. To do so, we implement a custom needlet internal linear combination (NILC) pipeline in a Python package, pyilc, which we make publicly available. We publicly release our Compton-y maps, which we construct using various constrained ILC ("deprojection") options in order to minimize contamination from the cosmic infrared background (CIB) in the reconstructed signal. In particular, we use a moment-based deprojection which minimizes sensitivity to the assumed frequency dependence of the CIB. Our code pyilc performs needlet or harmonic ILC on mm-wave sky maps in a flexible manner, with options to deproject various components on all or some scales. We validate our maps and compare them to the official Planck 2015 y-map, finding that we obtain consistent results on large scales and 10-20% lower noise on small scales. We expect that these maps will be useful for many auto- and cross-correlation analyses; in a companion paper, we use them to measure the tSZ -- CMB lensing cross-correlation. We anticipate that pyilc will be useful both for data analysis and for pipeline validation on simulations to understand the propagation of foreground components through a full NILC pipeline.

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