# Mathieu Remazeilles

**Research Fellow**

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**Contact**

I am a Research Fellow in cosmology at the Jodrell Bank Centre for Astrophysics at the University of Manchester.

Previously, I held postdoctoral Research Associate positions at the University of Manchester (2013-2020), the IAS in Orsay (2011-2013), and the APC in Paris (2009-2011), and worked as a Planck Scientist for the ESA's *Planck* space mission since 2011. I obtained my PhD in Theoretical Physics in 2009 from the University of Paris 11 at the LPT in Orsay, under the supervision of Martin A. Bucher.

My research revolves around the extraction and interpretation of new cosmological observables and information that can be gleaned from submillimetre and radio observations of the early Universe, primarily out of Cosmic Microwave Background (CMB) data:
Component separation, primordial CMB B-modes, Sunyaev-Zeldovich effects, CMB spectral distortions, CMB lensing, 21-cm intensity mapping, *Planck* data analysis (also here and here), extra-dimensions and cosmological perturbations.

__ Publication highlights__:

**A new semi-blind component separation method using moment expansion to deal with foreground spectral distortions due to line-of-sight integration and beam convolution**

By combining statistical moment expansion of the foreground emission and constrained ILC method, we have devised a new map-based semi-blind component separation method, called cMILC ("Constrained Moment ILC"), to deal with foreground spectral distortions beyond the leading-order SED which arise from the integration of multiple spectral contributions along the line-of-sight and across the angular beam. At the intersection of blind and parametric methods, the cMILC method allows to deproject the main moments of the foregrounds due to line-of-sight integration and beam convolution, and helps reducing quite significantly the residual foreground contamination in the recovery of primordial CMB B-modes.

*Remazeilles, Rotti, Chluba,*

*"Peeling off foregrounds with the constrained moment ILC method to unveil primordial CMB B modes", MNRAS (2021)*

**ESA Voyage 2050 White Paper: A space mission to map the entire observable universe using the CMB as a backlight**

We just submitted the Science White Paper "CMB Backlight" in response to the ESA Voyage 2050 call for long-term missions planning, in which we describe the various science possibilities that can be realized in cosmology in the next decades with an L-class space observatory that is dedicated to the study of the interactions of the CMB photons with the cosmic web. Our aim is to use the CMB as a "backlight" to probe the total mass, gas, and stellar content across the entire observable Universe, by means of analyzing the spatial and spectral distortions imprinted on the CMB.

*Basu, Remazeilles, Melin, et al,*

*"A Space Mission to Map the Entire Observable Universe using the CMB as a Backlight", arXiv:1909.01592 (2019)*

**Mapping the relativistic electron gas temperature across the sky**

We have developed a new map-based method that allows mapping the relativistic electron gas temperature of galaxy clusters across the entire sky with the relativistic SZ effect, and the diffuse electron gas temperature across a broad range of angular scales. The electron-temperature power spectrum provides a novel independent map-based observable that will complement the usual Compton-*y* observable to constrain cosmological parameters and break parameter degeneracies with future cosmological analyses of galaxy clusters. The recovered temperatures of a large sample of clusters will offer a new way for determining cluster masses using the relativistic SZ effect. The recovered SZ temperature profile of individual clusters will allow to break the degeneracy between electron density and temperature in the cluster pressure profile, and as a consequence the degeneracy between electron density and velocity profiles in the kinetic SZ effect.

*Remazeilles and Chluba,*

*"Mapping the relativistic electron gas temperature across the sky", MNRAS (2020)*

**Impact on**

**σ**

_{8}

**of relativistic temperature corrections in cosmological SZ analyses of galaxy clusters**

We have revisited the Planck SZ *y*-map power spectrum analysis by accounting for relativistic temperature corrections, showing that relativistic SZ corrections could alleviate the tension on σ_{8} between CMB and SZ probes. We have also predicted the relevant average cluster temperature across angular scales for SZ power spectrum analyses, and shown that it offers a new way to break the spectral degeneracy between mass-bias and σ_{8}.

*Remazeilles, Bolliet, Rotti, Chluba,*

*"Can we neglect relativistic temperature corrections in the Planck thermal SZ analysis?", MNRAS (2019)*

**Unveiling anisotropic**

*μ*-type spectral distortions We propose a solution to detect foreground-obscured *μ*-type spectral distortion anisotropies with future CMB satellites through the enhanced *μ*-*T* cross power spectrum, with vanishing residual *TT* correlations, and to constrain primordial non-Gaussianity on very small scales.

*Remazeilles and Chluba,*

*"Extracting foreground-obscured μ-distortion anisotropies to constrain primordial non-Gaussianity", MNRAS (2018)*

**Exploring Cosmic Origins with CORE: B-mode Component Separation**

A comprehensive study of the foregrounds and the component separation problem for the search for primordial CMB B-modes, in the context of the proposed CMB space mission CORE.

*Remazeilles et al. (100+ co-authors),*

*"Exploring Cosmic Origins with CORE: B-mode Component Separation", JCAP 04 023 (2018)*

**Disentangling Galactic dust emission and CIB anisotropies in Planck all-sky observations**

By applying the component separation method GNILC (*Remazeilles et al 2011b*) to Planck data, we have managed to disentangle the cosmic infrared background (CIB) and Galactic dust emissions over the full sky. We have obtained new estimates of dust temperature and emissivity, with reduced CIB contamination.
The GNILC dust and CIB all-sky maps have been publicly released on the Planck Legacy Archive (see Release PR2 - 2015, Foreground maps, dust or CIB), and featured on the front cover of A&A (vol. 596, Dec 2016)

*Planck Collaboration (corresponding author: Remazeilles),*

*"Planck intermediate results. XLVIII. Disentangling Galactic dust emission and cosmic infrared background anisotropies", A&A 596, A109 (2016)*

**Forecasts on the tensor-to-scalar ratio for future CMB B-mode polarization satellites**

We have compared the sensitivity to the tensor-to-scalar ratio of different CMB B-mode satellite concepts after foreground removal.

We have also quantified the impact on the tensor-to-scalar ratio of incorrect foreground modelling.

*Remazeilles, Dickinson, Eriksen, Wehus,*

*"Sensitivity and foreground modelling for large-scale CMB B-mode polarization satellite missions", MNRAS (2016)*

**The Planck Sunyaev-Zeldovich all-sky map**

Using a needlet internal linear combination (NILC) algorithm (*Remazeilles et al 2011a*), we have released the first thermal Sunyaev-Zeldovich (SZ) all-sky map, from which we derived new constraints on the amplitude of dark matter fluctuations.
Please follow this link to download the Planck NILC SZ map.

*Planck Collaboration (co-corresponding author: Remazeilles),*

*"Planck 2015 results. XXII. A map of the thermal Sunyaev-Zeldovich effect", A&A 594, A22 (2016)*

**The Reprocessed Haslam 408 MHz all-sky map**

We have reprocessed the Haslam et al map to release a significantly improved template of Galactic synchrotron radiation at 408 MHz in terms of subtraction of systematics and extra-galactic radio sources. Please download the Reprocessed Haslam 408 MHz map on the NASA LAMBDA dedicated webpage.

*Remazeilles et al.,*

*"An improved source-subtracted and destriped 408 MHz all-sky map", MNRAS (2015)*