The Spectrum of the Universe

Abstract

The cosmic background (CB) radiation, encompassing the sum of emission from all sources outside our own Milky Way galaxy across the entire electromagnetic spectrum, is a fundamental phenomenon in observational cosmology. Many experiments have been conceived to measure it (or its constituents) since the extragalactic Universe was first discovered; in addition to estimating the bulk (cosmic monopole) spectrum, directional variations have also been detected over a wide range of wavelengths. Here we gather the most recent of these measurements and discuss the current status of our understanding of the CB from radio to $\gamma$-ray energies. Using available data in the literature we piece together the sky-averaged intensity spectrum, and discuss the emission processes responsible for what is observed. We examine the effect of perturbations to the continuum spectrum from atomic and molecular line processes and comment on the detectability of these signals. We also discuss how one could in principle obtain a complete census of the CB by measuring the full spectrum of each spherical harmonic expansion coefficient. This set of spectra of multipole moments effectively encodes the entire statistical history of nuclear, atomic and molecular processes in the Universe.

33 pages, 15 figures, submitted to Applied Spectroscopy. Accepted and published in Applied Spectroscopy; new version reflects published version with some references added and typos corrected

References in corpus (50)

• Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
• The synthesis of the cosmic X-ray background in the Chandra and XMM-Newton era
• The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV
• Toward the Standard Population Synthesis Model of the X-Ray Background: Evolution of X-Ray Luminosity and Absorption Functions of Active Galactic Nuclei Including Compton-Thick Populations
• The Cosmic Infrared Background Resolved by Spitzer. Contributions of Mid-Infrared Galaxies to the Far-Infrared Background
• Baryon Acoustic Oscillation Intensity Mapping as a Test of Dark Energy
• Measurement of 21 cm brightness fluctuations at z ~ 0.8 in cross-correlation
• The Global 21 Centimeter Background from High Redshifts
• How accurately can 21 cm tomography constrain cosmology?
• Cosmic X-ray background and Earth albedo Spectra with Swift/BAT
• The Origin of the Extragalactic Gamma-Ray Background and Implications for Dark-Matter Annihilation
• Evolution of the 21 cm signal throughout cosmic history
• The extragalactic background light revisited and the cosmic photon-photon opacity
• Over half of the far-infrared background light comes from galaxies at z >= 1.2
• The Neutral Hydrogen Cosmological Mass Density at z=5
• The HI content of star-forming galaxies at z = 0.24
• ALMA spectroscopic survey in the Hubble Ultra Deep Field: Continuum number counts, resolved 1.2-mm extragalactic background, and properties of the faintest dusty star forming galaxies
• Line-Intensity Mapping: 2017 Status Report
• Spitzer Deep and Wide Legacy Mid- and Far-Infrared Number Counts and Lower Limits of Cosmic Infrared Background
• New synthesis models of consistent extragalactic background light over cosmic time
• On the Origin of Near-Infrared Extragalactic Background Light Anisotropy
• Damped Lyman-alpha absorbers as a probe of stellar feedback
• 21 cm signal from cosmic dawn: Imprints of spin temperature fluctuations and peculiar velocities
• The Chandra COSMOS legacy survey: Energy Spectrum of the Cosmic X-ray Background and constraints on undetected populations
• Correlated Anisotropies in the Cosmic Far-Infrared Background Detected by MIPS/Spitzer: Constraint on the Bias
• Carbon monoxide line emission as a CMB foreground: tomography of the star-forming universe with different spectral resolutions
• Intensity mapping of [CII] from early galaxies
• Cross-correlations as a cosmological carbon monoxide detector
• Cosmological hydrogen recombination: populations of the high level sub-states
• The contribution of the Unresolved Extragalactic Radio Sources to the Brightness Temperature of the sky
• Effects of primordial chemistry on the cosmic microwave background
• Carbon Monoxide Intensity Mapping at Moderate Redshifts
• The Resolved Near-Infrared Extragalactic Background
• The Resolved NIR Extragalactic Background
• Constraints on the Cosmic Near Infrared Background Excess from NICMOS Deep Field Observations
• The SCUBA-2 Cosmology Legacy Survey: The EGS deep field I - Deep number counts and the redshift distribution of the recovered Cosmic Infrared Background at 450 and 850 um
• Mapping the Diffuse Ultraviolet Sky with GALEX
• The Radio Synchrotron Background: Conference Summary and Report
• Ultraviolet to optical diffuse sky emission as seen by the Hubble Space Telescope Faint Object Spectrograph
• The narrow Fe K$\alpha$ line and the molecular torus in active galactic nuclei - an IR/X-ray view
• Measuring Galaxy Clustering and the Evolution of [CII] Mean Intensity with far-IR Line Intensity Mapping During 0.5 < z < 1.5
• The Cosmic Microwave Background for Pedestrians: A Review for Particle and Nuclear Physicists
• The Mystery of the Cosmic Diffuse Ultraviolet Background Radiation
• The Deep Diffuse Extragalactic Radio Sky at 1.75 GHz
• AKARI Observation of the Sub-degree Scale Fluctuation of the Near-infrared Background
• Ultra deep AKARI observations of Abell 2218: resolving the 15 um extragalactic background light
• Determination of the Far-Infrared Cosmic Background Using COBE/DIRBE and WHAM Data
• Can the 21 cm signal probe Population III and II star formation?
• Cosmic Gamma-ray Background Radiation
• The Far-Infrared Surveyor Mission Study: Paper I, the Genesis

Cited by in corpus (47)

• Planck 2018 results. I. Overview and the cosmological legacy of Planck
• Looking forward to Lepton-flavor-violating ALPs
• Dark Quark Nuggets
• Galaxy And Mass Assembly (GAMA): Assimilation of KiDS into the GAMA database
• Exploring New Physics with O(keV) Electron Recoils in Direct Detection Experiments
• The Irreducible Axion Background
• Primordial black hole constraints with Hawking radiation -- a review
• Probing the Blue Axion with Cosmic Optical Background Anisotropies
• Dynamical evolution of axion condensates under stimulated decays into photons
• GAMA/DEVILS: Constraining the cosmic star-formation history from improved measurements of the 0.3-2.2 micron Extragalactic Background Light
• Six Flavor Quark Matter
• Microwave Spectro-Polarimetry of Matter and Radiation across Space and Time
• Searching for Decaying and Annihilating Dark Matter with Line Intensity Mapping
• Challenges and Opportunities of Gravitational Wave Searches above 10 kHz
• Gamma-ray Cosmology and Tests of Fundamental Physics
• Light Primordial Exotic Compact Objects as All Dark Matter
• Extragalactic Background Light: Inventory of light throughout the cosmic history
• Limits on High-Frequency Gravitational Waves in Planetary Magnetospheres
• Gravitational wave search through electromagnetic telescopes
• Gamma-Ray Astrophysics
• GAMA/DEVILS: Cosmic star formation and AGN activity over 12.5 billion years
• An updated estimate of the cosmic radio background and implications for ultra-high-energy photon propagation
• Tidal Love numbers and approximate universal relations for fermion soliton stars
• ART${}^2$: A 3D Parallel Multi-wavelength Radiative Transfer Code for Continuum and Atomic and Molecular Lines
• The cosmic radio background from 150 MHz--8.4 GHz, and its division into AGN and star-forming galaxy flux
• Novel bounds on decaying axionlike particle dark matter from the cosmic background
• SKYSURF-4: Panchromatic HST All-Sky Surface-Brightness Measurement Methods and Results
• Have we seen all the galaxies that comprise the cosmic infrared background at 250\,$\mu$m $\le \lambda \le$ 500\,$\mu$m?
• SKYSURF-3: Testing Crowded Object Catalogs in the Hubble eXtreme Deep Field Mosaics to Study Sample Incompleteness from an Extragalactic Background Light Perspective
• Explaining Xenon-1T signal with FIMP dark matter and neutrino mass in a $U(1{)}_X$ extension
• Constraints on galaxy formation from the cosmic-far-infrared-background\,$-$\,optical-imaging cross-correlation using \textit{Herschel} and UNIONS
• ISW in $\Lambda$CDM or something else?
• SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES). V. Confusion-limited Submillimeter Galaxy Number Counts at 450 $\mu$m and Data Release for the COSMOS Field
• Constraining gravitational-wave backgrounds from conversions into photons in the Galactic magnetic field
• The Glow of Axion Quark Nugget Dark Matter: (I) Large Scale Structures
• A deep-learning approach to the 3D reconstruction of dust density and temperature in star-forming regions
• Forecasts for Broadband Intensity Mapping of the Ultraviolet-Optical Background with CASTOR and SPHEREx
• Upcoming searches for decaying dark matter with ULTRASAT ultraviolet maps
• The Cosmic Infrared Background Experiment-2: An Intensity Mapping Optimized Sounding-rocket Payload to Understand the Near-IR Extragalactic Background Light
• Constraining $z\lesssim 2$ ultraviolet emission with the upcoming ULTRASAT satellite
• The case for a 'sub-millimeter SDSS': a 3D map of galaxy evolution to z~10
• SKYSURF. X. A Novel Method for Measuring Integrated Galaxy Light
• Constraints on High-Frequency Gravitational Waves from Graviton-Photon Conversion in the M87 Galaxy
• A generalized Higgs potential with two degenerate minima for a dark QCD matter scenario
• Lyman-alpha Filter Prototype to Enable Astronomical Photometry in the Lyman Ultraviolet
• Intermediate-mass black holes and contribution to extragalactic background light from Population III stars in Milky Way-like galaxies
• Viability of quantum communication across interstellar distances