Far Infrared Absolute Spectrophotometer Research Articles

Constraints on primordial black holes with CMB spectral distortions

In the mixed dark matter scenarios consisting of primordial black holes (PBHs) and weakly interacting massive particles (WIMPs), WIMPs can be accreted onto PBHs to form ultracompact minihalos (UCMHs) with a density spike in the early universe. Compared with the classical dark matter halo, UCMHs are formed earlier and have a higher density of center. Since the annihilation rate is proportional to the squared number density of WIMPs, it is expected that WIMPs annihilation within UCMHs is enhanced and has influences on the early universe. Between the time of recombination and matter-radiation equality, the energy released from WIMPs annihilation within UCMHs is injected into the Universe resulting in cosmic microwave background $y$-type distortion. We investigate these effects and derive the upper limits on the abundance of PBHs taking advantage of the observational results of a far infrared absolute spectrophotometer (FIRAS). We find that for the WIMPs mass range $1\ensuremath{\le}{m}_{\ensuremath{\chi}}\ensuremath{\le}1000\text{ }\text{ }\mathrm{GeV}$, the upper limits on the abundance of PBHs are $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\ensuremath{\le}{\mathrm{\ensuremath{\Omega}}}_{\mathrm{PBH}}\ensuremath{\le}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$.

Is there evidence for a hotter Universe?

The measurement of present-day temperature of the Cosmic Microwave Background (CMB), T_0 = 2.72548 pm 0.00057 K (1sigma ), made by the Far-InfraRed Absolute Spectrophotometer (FIRAS) as recalibrated by the Wilkinson Microwave Anisotropy Probe (WMAP), is one of the most precise measurements ever made in Cosmology. On the other hand, estimates of the Hubble Constant, H_0, obtained from measurements of the CMB temperature fluctuations assuming the standard varLambda CDM model exhibit a large (4.1sigma ) tension when compared with low-redshift, model-independent observations. Recently, some authors argued that a slightly change in T_0 could alleviate or solve the H_0-tension problem. Here, we investigate evidence for a hotter or colder universe by performing an independent analysis from currently available temperature-redshift T(z) measurements. Our analysis (parametric and non-parametric) shows a good agreement with the FIRAS measurement and a discrepancy of ge 1.9sigma from the T_0 values required to solve the H_0 tension. This result reinforces the idea that a solution of the H_0-tension problem in fact requires either a better understanding of the systematic errors on the H_0 measurements or new physics.

How to measure CMB spectral distortions with an imaging telescope

We propose the implementation of an imaging telescope in combination with an inter-frequency calibrator to measure the spectral shape of the microwave sky by exploiting the differences in the sky intensity between multiple pairs of frequency channels. By jointly sampling the cosmological and foreground parameters in a Bayesian framework for $600$ instrument configurations, we determine the minimum calibration accuracy required in order to obtain measurements of spectral distortions and simultaneously measure spectral and spatial fluctuations of the CMB. We demonstrate the feasibility of this technique for a CMB mission like PICO (Probe of Inflation and Cosmic Origins), and show that a $10$-$\sigma$ measurement of the $y$-distortion along with a two orders of magnitude improvement on the FIRAS (Far-Infrared Absolute Spectrophotometer) $\mu$-distortion limit is feasible from this technique. We argue that longer term applications may be envisaged at even higher sensitivity, capable of attaining the $\mu$-distortion that provide a robust prediction of the $\Lambda$CDM model and even primordial recombination lines of hydrogen and helium, in the context of the ESA (European Space Agency) Voyage 2035-2050 program.

Constraints on Dark Matter Interactions with Standard Model Particles from Cosmic Microwave Background Spectral Distortions.

We propose a new method to constrain elastic scattering between dark matter (DM) and standard model particles in the early Universe. Direct or indirect thermal coupling of nonrelativistic DM with photons leads to a heat sink for the latter. This results in spectral distortions of the cosmic microwave background (CMB), the amplitude of which can be as large as a few times the DM-to-photon-number ratio. We compute CMB spectral distortions due to DM-proton, DM-electron, and DM-photon scattering for generic energy-dependent cross sections and DM mass m_{χ}≳1 keV. Using Far-Infrared Absolute Spectrophotometer measurements, we set constraints on the cross sections for m_{χ}≲0.1 MeV. In particular, for energy-independent scattering we obtain σ_{DM-proton}≲10^{-24} cm^{2} (keV/m_{χ})^{1/2}, σ_{DM-electron}≲10^{-27} cm^{2} (keV/m_{χ})^{1/2}, and σ_{DM-photon}≲10^{-39} cm^{2} (m_{χ}/keV). An experiment with the characteristics of the Primordial Inflation Explorer would extend the regime of sensitivity up to masses m_{χ}~1 GeV.

Chameleon-photon mixing in a primordial magnetic field

We consider the non-resonant mixing between photons and scalar ALPs with masses much less than the plasma frequency along the path, with specific reference to the chameleon scalar field model. The mixing would alter the intensity and polarization state of the cosmic microwave background (CMB) radiation. We find that the average modification to the CMB polarization modes is negligible. However the average modification to the CMB intensity spectrum is more significant and we compare this to high precision measurements of the CMB monopole made by the far infrared absolute spectrophotometer (FIRAS) on board the COBE satellite. The resulting 95\% confidence limit on the scalar-photon conversion probability in the primordial field (at 100 GHz) is P < 2.6x10^{-2}. This corresponds to a degenerate constraint on the photon-scalar coupling strength, g, and the magnitude of the primordial magnetic field. Taking the upper bound on the strength of the primordial magnetic field derived from the CMB power spectra, B < 5.0x10^{-9}G, this would imply an upper bound on the photon-scalar coupling strength in the range g < 7.14x10^{-13}GeV^{-1} to g < 9.20x10^{-14}GeV^{-1}, depending on the power spectrum of the primordial magnetic field.

Relic density and CMB constraints on dark matter annihilation with Sommerfeld enhancement

We calculate how the relic density of dark matter particles is altered when their annihilation is enhanced by the Sommerfeld mechanism due to a Yukawa interaction between the annihilating particles. Maintaining a dark matter abundance consistent with current observational bounds requires the normalization of the $s$-wave annihilation cross section to be decreased compared to a model without enhancement. The level of suppression depends on the specific parameters of the particle model, with the kinetic decoupling temperature having the most effect. We find that the cross section can be reduced by as much as an order of magnitude for extreme cases. We also compute the $\ensuremath{\mu}$-type distortion of the CMB energy spectrum caused by energy injection from such Sommerfeld-enhanced annihilation. Our results indicate that in the vicinity of resonances, associated with bound states, distortions can be large enough to be excluded by the upper limit $|\ensuremath{\mu}|\ensuremath{\le}9.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ found by the FIRAS (Far Infrared Absolute Spectrophotometer) instrument on the COBE (Cosmic Background Explorer) satellite.

Nobel Lecture: From the Big Bang to the Nobel Prize and beyond

NASA's Cosmic Background Explorer satellite mission, the COBE, laid the foundations for modern cosmology by measuring the spectrum and anisotropy of the cosmic microwave background radiation and discovering the cosmic infrared background radiation. I describe the history of the COBE project, its scientific context, the people who built it, and the scientific results. The COBE observed the universe on the largest scales possible by mapping the cosmic microwave and infrared background radiation fields and determining their spectra. It produced conclusive evidence that the hot Big Bang theory of the early universe is correct, showed that the early universe was very uniform but not perfectly so, and that the total luminosity of post--Big Bang objects is twice as great as previously believed. The COBE concept was developed by a Mission Definition Study Team appointed by NASA in 1976, based on three competing proposals submitted in 1974. The COBE was built in-house by Goddard Space Flight Center, with a helium cryostat provided by Ball Aerospace, and was launched on a Delta rocket built by McDonnell Douglas. It is in a circular orbit $900\phantom{\rule{0.3em}{0ex}}\mathrm{km}$ above the Earth, in a plane inclined 99\ifmmode^\circ\else\textdegree\fi{} to the equator and roughly perpendicular to the line to the Sun. It carried three instruments, a far infrared absolute spectrophotometer (FIRAS), a differential microwave radiometer with three channels (DMR), and a diffuse infrared background experiment (DIRBE). The helium cryostat cooled the FIRAS and DIRBE for $10\phantom{\rule{0.3em}{0ex}}\text{months}$ until the helium was exhausted, but operations continued for a total of $4\phantom{\rule{0.3em}{0ex}}\text{years}$. Subsequent observations have confirmed the COBE results and led to measurements of the main cosmological parameters with a precision of a few percent.

Dust from reionization

The possibility that population III stars have reionized the Universe at redshifts greater than 6 has recently gained mo- mentum with WMAP polarization results. Here we analyse the role of early dust produced by these stars and ejected into the in- tergalactic medium. We show that this dust, heated by the radiation from the same population III stars, produces a submillimetre excess. The electromagnetic spectrum of this excess could account for a significant fraction of the FIRAS (Far Infrared Absolute Spectrophotometer) cosmic far infrared background above 700 micron. This spectrum, a primary anisotropy (∆T ) spectrum times the ν 2 dust emissivity law, peaking in the submillimetre domain around 750 micron, is generic and does not depend on other detailed dust properties. Arcminute-scale anisotropies, coming from inhomogeneities in this early dust, could be detected by future submillimetre experiments such as Planck HFI.

COBE observations of the cosmic infrared background

The diffuse infrared background experiment (DIRBE) on the COsmic Background Explorer (COBE) measured the total infrared signal seen from space at a distance of 1 AU from the Sun. Using time variations as the Earth went around the Sun, it is possible to remove most of the foreground signal produced by the interplanetary dust cloud [zodiacal light]. By correlating the DIRBE signal with the column density of atomic hydrogen measured using the 21 cm line, it is possible to remove most of the foreground signal produced by interstellar dust, although one must still be concerned by dust associated with H 2 (molecular gas) and H II (the warm ionized medium). DIRBE was not able to determine the cosmic infrared background (CIRB) in the 5–60 μm wavelength range, but does detect both a far infrared background and a near infrared background. The far infrared background has an integrated intensity of about 34 nW/m 2/sr, while the near infrared and optical extragalactic background has about 59 nW/m 2/sr. The far infrared absolute spectrophotometer (FIRAS) on COBE has been used to constrain the long wavelength tail of the far infrared background but a wide range of intensities at 850 μm are compatible with the FIRAS data. Thus the fraction of the CIRB produced by SCUBA sources has large uncertainties in both the numerator and the denominator.

The Spectrum of the Cosmic Microwave Background Anisotropy from the Combined COBE FIRAS and WMAP Observations

The cosmic microwave background (CMB) anisotropy data from the COBE Far Infrared Absolute Spectrophotometer (FIRAS) is reanalyzed in light of the Wilkinson Microwave Anisotropy Probe (WMAP) observations. The frequency spectrum of the FIRAS signal that has the spatial distribution seen by WMAP is shown to be consistent with CMB temperature fluctuations well into the Wien region of the spectrum. The consistency of these data, from very different instruments with very different observing strategies, provides compelling support for the interpretation that the signal seen by WMAP is temperature anisotropy of cosmological origin. The data also limit rms fluctuations in the Compton y parameter, observable via the Sunyaev-Zeldovich effect, to Δy < 3 × 10-6 (95% confidence level) on ~5° angular scales.

The Spectral Results of the Far‐Infrared Absolute Spectrophotometer Instrument onCOBE

The cosmic microwave background (CMB) spectral results of the Far-Infrared Absolute Spectrophotometer (FIRAS) instrument are summarized. Some questions that have been raised about the calibration accuracy are also addressed. Finally, we comment on the potential for major improvements with new measurement approaches. The measurement of the deviation of the CMB spectrum from a 2.725 ± 0.001 K blackbody form made by the COBE-FIRAS could be improved by nearly 2 orders of magnitude.

The Far Infrared and Submillimeter Diffuse Extragalactic Background

The cosmic infrared background (CIB) radiation was a long-sought fossil of energetic processes associated with structure formation and chemical evolution since the Big Bang. The COBE Diffuse Infrared Background Experiment (DIRBE) and Far Infrared Absolute Spectrophotometer (FIRAS) were specifically designed to search for this background from 1.25 μm to millimeter wavelengths. These two instruments provided high quality, absolutely calibrated all-sky maps which have enabled the first detections of the CIB, initially at far infrared and submillimeter wavelengths, and more recently in the near infrared as well. The aim of this paper is to review the status of determinations of the CIB based upon COBE measurements. The results show that the energy in the CIB from far infrared to millimeter wavelengths is comparable to that in the integrated light of galaxies from UV to near infrared wavelengths: the universe had a luminous but dusty past. On the assumption that nucleosynthesis in stars is the energy source for most of this light, the results also imply that 1–8% of cosmic baryons has been converted to helium and heavier elements in stars. The integrated background light from UV to millimeter wavelengths, 60–120 nW m−2 sr−1, is about 10% of that in the cosmic microwave background. Current knowledge of the CIB provides significant new constraints on models of the history of star formation and galaxy evolution.

COBEFar Infrared Absolute Spectrophotometer Observations of Galactic Lines

The COBE Far Infrared Absolute Spectrophotometer (FIRAS) observations constitute an unbiased survey over the wavelength range from 100 μm to 1 cm over 99% of the sky. Improved calibration of the FIRAS instrument and the inclusion of all of the FIRAS data allow an improved signal-to-noise ratio determination of the spectral lines by a factor of ~2 over our previous results. The resolution is low (0.45 cm-1), so only the strongest lines are observable. The CO chain from J = 1-0 to J = 8-7 is observed toward the Galactic center. The line ratios are roughly consistent with a 40 K excitation temperature. The 157.7 μm C II and 205.3 μm N II lines are observable over most of the sky. The 370.4 and 609.1 μm lines of C I and the 121.9 μm line of N II are observed in the Galactic plane. The line ratios at the Galactic center are consistent with a density of n0 ~ 30 cm-3 and a UV flux of G0 ≈ 15 μW m-2 sr-1 (10 Habing units). The 269 μm H2O line is observed toward the Galactic center in absorption.

The Canada‐UK Deep Submillimeter Survey: First Submillimeter Images, the Source Counts, and Resolution of the Background

We present the first results of a deep unbiased submillimeter survey carried out at 450 and 850 μm. We detected 12 sources at 850 μm at greater than the 3 σ level, giving a surface density of sources with S850μm>2.8 mJy of 0.49 ± 0.16 arcmin-2. If replicated over the sky, our sources would generate a background at 850 μm of 9.6 × 10−11 W m-2 sr-1, which is ≃20% of the value measured by the Far-Infrared Absolute Spectrophotometer (FIRAS) and a significant fraction of the total background radiation produced by stars. This implies, through the connection between metallicity and background radiation, that a significant fraction of all the stars that have ever been formed were formed in objects like those detected here. The combination of their large contribution to the background radiation and their extreme bolometric luminosities makes these objects excellent candidates for being proto-elliptical galaxies. Optical astronomers have recently shown that the UV luminosity density of the universe increases by a factor of ≃10 between z=0 and z=1-2 and then decreases again at higher redshifts. Using the results of a parallel submillimeter survey of the local universe, we show that both the submillimeter source density and background radiation (as detected by FIRAS) can be explained if the submillimeter luminosity density evolves in a similar way to the UV luminosity density. Thus, if these sources are elliptical galaxies in the process of formation, they are probably forming at relatively modest redshifts.

Calibrator Design for theCOBEFar‐Infrared Absolute Spectrophotometer (FIRAS)

The photometric errors of the external calibrator for the Far Infrared Absolute Spectrophotometer (FIRAS) instrument on the COBE are smaller than the measurement errors on the cosmic microwave background radiation (CMBR) spectrum (typically 0.02 MJy sr-1, 1 σ) and smaller than 0.01% of the peak brightness of the CMB. The calibrator is a reentrant cone, shaped like a trumpet mute, made of Eccosorb iron-loaded epoxy. It fills the entire beam of the instrument and is the source of its accuracy. Its known errors are caused by reflections, temperature gradients, and leakage through the material and around the edge. Estimates and limits are given for all known error sources. Improvements in understanding the temperature measurements of the calibrator allow an improved CMB temperature determination of 2.725±0.002 K.

TheCOBEDiffuse Infrared Background Experiment Search for the Cosmic Infrared Background. IV. Cosmological Implications

A direct measurement of the extragalactic background light (EBL) can provide important constraints on the integrated cosmological history of star formation, metal and dust production, and the conversion of starlight into infrared emission by dust. In this paper we examine the cosmological implications of the recent detection of the EBL in the 125 to 5000 ?m wavelength region by the Diffuse Infrared Background Experiment (DIRBE) and Far Infrared Absolute Spectrophotometer (FIRAS) on board the Cosmic Background Explorer (COBE). We first show that the 140 and 240 ?m isotropic residual emission found in the DIRBE data cannot be produced by foreground emission sources in the solar system or the Galaxy. The DIRBE 140 and 240 ?m isotropic residuals, and by inference the FIRAS residuals as well, are therefore extragalactic. Assuming that most of the 140 and 240 ?m emission is from dust yields a 2 ? lower limit of ?I(?) ? 5 nW m-2 sr-1 for the EBL at 100 ?m. The integrated EBL detected by the COBE between 140 and 5000 ?m is ~16 nW m-2 sr-1, roughly 20%-50% of the integrated EBL intensity expected from energy release by nucleosynthesis throughout cosmic history. This also implies that at least ~5%-15% of the baryonic mass density implied by big bang nucleosynthesis has been processed through stars. The COBE observations provide important constraints on the cosmic star formation rate, and we calculate the EBL spectrum for various star formation histories. The results show that the UV and optically determined cosmic star formation rates fall short in producing the observed 140 to 5000 ?m background. The COBE observations require the star formation rate at redshifts of z ? 1.5 to be larger than that inferred from UV-optical observations by at least a factor of 2. This excess stellar energy must be mainly generated by massive stars, since it otherwise would result in a local K-band luminosity density that is larger than observed. The energy sources could either be yet undetected dust-enshrouded galaxies, or extremely dusty star-forming regions in observed galaxies, and they may be responsible for the observed iron enrichment in the intracluster medium. The exact star formation history or scenarios required to produce the EBL at far-IR wavelengths cannot be unambiguously resolved by the COBE observations and must await future observations.

Cosmic microwave background theory

A long-standing goal of theorists has been to constrain cosmological parameters that define the structure formation theory from cosmic microwave background (CMB) anisotropy experiments and large-scale structure (LSS) observations. The status and future promise of this enterprise is described. Current band-powers in -space are consistent with a DeltaT flat in frequency and broadly follow inflation-based expectations. That the levels are approximately (10(-5))2 provides strong support for the gravitational instability theory, while the Far Infrared Absolute Spectrophotometer (FIRAS) constraints on energy injection rule out cosmic explosions as a dominant source of LSS. Band-powers at 100 suggest that the universe could not have re-ionized too early. To get the LSS of Cosmic Background Explorer (COBE)-normalized fluctuations right provides encouraging support that the initial fluctuation spectrum was not far off the scale invariant form that inflation models prefer: e.g., for tilted Lambda cold dark matter sequences of fixed 13-Gyr age (with the Hubble constant H0 marginalized), ns = 1.17 +/- 0.3 for Differential Microwave Radiometer (DMR) only; 1.15 +/- 0.08 for DMR plus the SK95 experiment; 1.00 +/- 0.04 for DMR plus all smaller angle experiments; 1.00 +/- 0.05 when LSS constraints are included as well. The CMB alone currently gives weak constraints on Lambda and moderate constraints on Omegatot, but theoretical forecasts of future long duration balloon and satellite experiments are shown which predict percent-level accuracy among a large fraction of the 10+ parameters characterizing the cosmic structure formation theory, at least if it is an inflation variant.

The Cosmic Microwave Background Spectrum from the FullCOBEFIRAS Data Set

We have refined the analysis of the data from the FIRAS (Far-InfraRed Absolute Spectrophotometer) on board the COBE (COsmic Background Explorer). The FIRAS measures the difference between the cosmic microwave background and a precise blackbody spectrum. We find new, tighter upper limits on general deviations from a blackbody spectrum. The rms deviations are less than 50 parts per million of the peak of the cosmic microwave background radiation. For the Comptonization and chemical potential, we find |y| < 15 × 10–6 and |μ| < 9 × 10–5 (95% confidence level [CL]). There are also refinements in the absolute temperature, 2.728 ± 0.004 K (95% CL), the dipole direction, (1, b)/(26414 ± 0.30, 4826 ± 0.30) (95% CL), and the amplitude, 3.372 ± 0.014 mK (95% CL). All of these results agree with our previous publications.

Measurement and Implications of the Cosmic Microwave Background Spectrum

The Cosmic Background Explorer (COBE) was developed by NASA Goddard Space Flight Center to measure the diffuse infrared and microwave radiation from the early universe. It also measured emission from nearby sources such as the stars, dust, molecules, atoms, ions, and electrons in the Milky Way, and dust and comets in the Solar System. It was launched 18 November 1989 on a Delta rocket, carrying one microwave instrument and two cryogenically cooled infrared instruments. The Far Infrared Absolute Spectrophotometer (FIRAS) mapped the sky at wavelengths from 0.01 to 1 cm, and compared the CMBR to a precise blackbody. The spectrum of the CMBR differs from a blackbody by less than 0.03%. The Differential Microwave Radiometers (DMR) measured the fluctuations in the CMBR originating in the Big Bang, with a total amplitude of 11 parts per million on a 10° scale. These fluctuations are consistent with scale-invariant primordial fluctuations. The Diffuse Infrared Background Experiment (DIRBE) spanned the wavelength range from 1.2 to 240 μm and mapped the sky at a wide range of solar elongation angles to distinguish foreground sources from a possible extragalactic Cosmic Infrared Background Radiation (CIBR). In this paper we summarize the COBE mission and describe the results from the FIRAS instrument. The results from the DMR and DIRBE were described by Smoot and Hauser at this Symposium.

Far-Infrared Spectral Observations of the Galaxy by the Far-Infrared Absolute Spectrophotometer

The Galactic continuum spectrum from 5–96 cm−1 is derived from COBE/FIRAS observations. The spectra are dominated by warm dust emission, which may be fit with a single temperature along each line of sight in the range 16–21 K. A widespread, very cold component (4–7 K) with optical depth that is spatially correlated with the warm component is also detected. The nature of the cold component and its implications for the amount of very cold material in the Milky Way are discussed.