[Paper Review] Microwave Spectro-Polarimetry of Matter and Radiation across Space and Time

Jacques Delabrouille, Maximilian H. Abitbol+78 more|arXiv (Cornell University)|Sep 4, 2019

Cosmology and Gravitation Theories195 references37 citations

TL;DR

Proposes a high-sensitivity, multi-instrument space mission to perform a full-sky, spectro-polarimetric census of matter and radiation from arcminute to full-sky scales across cosmic history using SZ effects, lensing, high-redshift emission, primary CMB, and spectral distortions.

ABSTRACT

This paper discusses the science case for a sensitive spectro-polarimetric survey of the microwave sky. Such a survey would provide a tomographic and dynamic census of the three-dimensional distribution of hot gas, velocity flows, early metals, dust, and mass distribution in the entire Hubble volume, exploit CMB temperature and polarisation anisotropies down to fundamental limits, and track energy injection and absorption into the radiation background across cosmic times by measuring spectral distortions of the CMB blackbody emission. In addition to its exceptional capability for cosmology and fundamental physics, such a survey would provide an unprecedented view of microwave emissions at sub-arcminute to few-arcminute angular resolution in hundreds of frequency channels, a data set that would be of immense legacy value for many branches of astrophysics. We propose that this survey be carried-out with a large space mission featuring a broad-band polarised imager and a moderate resolution spectro-imager at the focus of a 3.5m aperture telescope actively cooled to about 8K, complemented with absolutely-calibrated Fourier Transform Spectrometer modules observing at degree-scale angular resolution in the 10-2000 GHz frequency range. We propose two observing modes: a survey mode to map the entire sky as well as a few selected wide fields, and an observatory mode for deeper observations of regions of specific interest.

Motivation & Objective

• Motivate a comprehensive census of matter and radiation in the Universe from the last scattering surface to the present, using microwave spectro-polarimetry.
• Define observables (SZ effects, CMB lensing, high-redshift line emission, primary CMB, spectral distortions) to map the cosmic web in 3D over space and time.
• Outline mission concepts, instruments, and technology roadmap to achieve arcminute to degree-scale measurements across 10–2000 GHz.
• Highlight the scientific impact and legacy value across cosmology, astrophysics, and fundamental physics.

Proposed method

• Propose a space-based survey with three instruments observing 10–2000 GHz at varying spectral and angular resolutions.
• Use a large 3-m class cold telescope to achieve arcminute-scale resolution at 300 GHz for a broad-band polarimetric imager and a moderate-resolution filter-bank spectrometer.
• Incorporate an absolute spectroscopy Fourier-transform spectrometer (FTS) across the full band with high sensitivity, spanning 2.5–60 GHz spectral resolution.
• Enable 6 years of L2-orbit observations in survey and observatory modes, including a guest focal plane for additional science.
• Leverage prior mission concepts ( CORE, PICO, SPICA, PIXIE, PRISTINE) to inform instrument heritage and technology readiness.

Experimental results

Research questions

• RQ1 How can high-sensitivity, multi-frequency microwave observations enable a complete census of baryonic and dark matter structures across cosmic history?
• RQ2 What are the capabilities required (sensitivity, angular resolution, spectral resolution, frequency channels) to separate tSZ, kSZ, rSZ, ntSZ, and CIB signals and map gas, velocity fields, and lensing?
• RQ3 What is the realistic potential of CMB lensing, SZ tomography, and spectral distortions to constrain ΛCDM extensions and fundamental physics?
• RQ4 What mission design (instruments, survey strategy, duration) optimally delivers primary CMB precision, SZ diagnostics, and spectral distortion measurements from 10–2000 GHz?
• RQ5 How can the proposed observations address open cosmological questions such as inflation, dark matter/energy properties, and reionization history?

Key findings

• A full-sky, arcminute-resolution SZ and lensing census could detect all clusters above 5×10^13 Msun with y-parameter sensitivity δY500 ≈ 9×10^-7 and aspire to δY500 ≈ 5×10^-8.
• An angular resolution of about 1.5′ (goal 1′) is needed to recover cluster signals and measure kSZ effectively on relevant scales.
• A wide multi-channel survey (≈20 frequency bands from 50–800 GHz) is required to separate SZ, CIB, and foregrounds, with key channels at 150, 220, and 350 GHz.
• CMB lensing reconstruction benefits from high-sensitivity polarization measurements, with performance saturating at ~0.1–0.3 μK·arcmin for 4′ resolution and at ~3 μK·arcmin for TT maps at 2–4′ resolution.
• Absolute spectroscopy across 10–2000 GHz with an FTS could achieve 4–5 orders of magnitude better sensitivity than COBE-FIRAS, enabling precise spectral distortion studies and recombination radiation probes.
• The mission enables a transformative, legacy survey that constrains cosmology, structure formation, and fundamental physics beyond current capabilities.