PRISM (Polarized Radiation Imaging and Spectroscopy Mission): A White Paper on the Ultimate Polarimetric Spectro-Imaging of the Microwave and Far-Infrared Sky

TL;DR

PRISM proposes a large-class space mission to perform the ultimate spectro-polarimetric survey of the microwave and far-infrared sky, combining an ultra-sensitive all-sky polarimetric imager with an absolute spectrometer. It addresses questions from inflation and primordial B-modes to the evolution of galaxies via the SZ effect and CIB, to the structure of the Galactic ISM and dust physics, and to CMB spectral distortions encoding early-universe physics. The dual-instrument approach enables precise delensing, CMB lensing constraints, and a comprehensive legacy data set including a ~$10^{6}$ cluster catalog and deep multi-frequency ISM maps. The mission would significantly advance cosmology, galaxy evolution, and Galactic astrophysics, leveraging and complementing upcoming optical/IR surveys and ground-based facilities, with the potential to probe $r$ down to $3\times 10^{-4}$ and to map the early universe through spectral distortions and emission-line diagnostics.

Abstract

PRISM (Polarized Radiation Imaging and Spectroscopy Mission) was proposed to ESA in response to the Call for White Papers for the definition of the L2 and L3 Missions in the ESA Science Programme. PRISM would have two instruments: (1) an imager with a 3.5m mirror (cooled to 4K for high performance in the far-infrared---that is, in the Wien part of the CMB blackbody spectrum), and (2) an Fourier Transform Spectrometer (FTS) somewhat like the COBE FIRAS instrument but over three orders of magnitude more sensitive. Highlights of the new science (beyond the obvious target of B-modes from gravity waves generated during inflation) made possible by these two instruments working in tandem include: (1) the ultimate galaxy cluster survey gathering 10e6 clusters extending to large redshift and measuring their peculiar velocities and temperatures (through the kSZ effect and relativistic corrections to the classic y-distortion spectrum, respectively) (2) a detailed investigation into the nature of the cosmic infrared background (CIB) consisting of at present unresolved dusty high-z galaxies, where most of the star formation in the universe took place, (3) searching for distortions from the perfect CMB blackbody spectrum, which will probe a large number of otherwise inaccessible effects (e.g., energy release through decaying dark matter, the primordial power spectrum on very small scales where measurements today are impossible due to erasure from Silk damping and contamination from non-linear cascading of power from larger length scales). These are but a few of the highlights of the new science that will be made possible with PRISM.

Figures (7)

• Figure 1: Lower mass limits for detection of the indicated SZ effects at signal-to-noise $S/N>5$ as a function of redshift.
• Figure 2: SEDs of dusty galaxies (top panel) and of AGNs (bottom panel) at different redshifts compared with estimated $5\sigma$ detection limits (solid black line) taking into account instrumental and confusion noise summed in quadrature. The instrumental noise refers to the full mission. The $5\sigma$ detection limits allowing for either component are shown by the dotted and the dashed black lines, showing that PRISM is confusion limited above $\approx 150\,$GHz. We have assumed that component separation techniques, extensively validated both on simulations and on real data, can efficiently remove diffuse emissions such as the CMB (that would otherwise dominate the fluctuation field for $\nu\,\hbox{${<\atop\hbox{$\sim$}}$}\, 220\,$GHz) and Galactic emissions. In the top panel, at $z=0.1$ and 0.5 we have plotted the Arp 220 SED scaled to an IR (8--$1000\,\mu$m) luminosity of $10^{12}\,L_\odot$. At $z\ge 1$ we have used the SED of the $z\approx 2.3$ galaxy SMM J2135-0102 scaled to $L_{\rm IR}=10^{13}\,L_\odot$ for $z=1$ and $z=2$, and to $L_{\rm IR}=3\cdot 10^{13}\,L_\odot$Riechers2013 for $z\ge 3$. In the bottom panel, the solid colored lines represent SEDs of a type-2 QSO (contribution of the host-galaxy subtracted) with $L_{\rm IR}=10^{13}\,L_\odot$ at several redshifts $\ge 2$, while the dashed colored lines show a schematic representation of the SED of the prototype blazar 3C 273 shifted to redshifts from 1 to 5.
• Figure 3: Left: Constraints on inflationary potentials from Planck and the predicted constraints from PRISM (not assuming de-lensing) for a fiducial value of $r=5\times 10^{-2}$ (adapted from planck2013-p17). Right: distribution of inflationary model parameters generated using a model independent approach that Monte-Carlo samples the inflationary flow equations. While these simulations cannot be interpreted in a statistical way (e.g., 192627), they show that models cluster around attractor regions (adapted from ultimatepol).
• Figure 4: Reconstruction noise on the lensing deflection power spectrum forecast for the full Planck mission (four surveys; left) and PRISM (right) using temperature alone (red) and temperature and polarization (blue). For Planck we also show the approximate noise level for the temperature analysis of the nominal-mission data (red dashed) 2013arXiv1303.5077P, and for PRISM, we also show the approximate noise level (green) for an improved iterative version of the reconstruction estimator. The deflection power spectrum is plotted based on the linear matter power spectrum (black solid) and with non-linear corrections (black dashed).
• Figure 5: Planck CMB temperature bispectrum Planck2013ng (left) and primordial (right) and late-time (middle) non-Gaussian shapes Planck2013ng2013arXiv1303.5085P. Note the periodic CMB ISW-lensing signal (middle) in the squeezed limit along the edges, which is seen at the 2.5$\sigma$ level in the Planck bispectrum on the left. Scale-invariant signals predicted by many inflationary models are strongly constrained by the Planck bispectrum, although 'oscillatory' and 'flattened' features hint at new physics. An example of an inflationary 'feature' model is shown on the right. PRISM will probe these hints with an order of magnitude more resolved triangle configurations.