Cosmic infrared background

Finally, one of the instruments on COBE detected the presence of a cosmic infrared background (CIB), a remnant of the period during which the first stars began to form, many millions of years after the big bang itself. COBE was only one, albeit the best-known, of several research programs designed to study the CMB. In 1998, for example, two other research teams made use of balloons released into the stratosphere to study the cosmic microwave background. These... 

Fig. 1.1 Schematic Spectral Eneigy Distributions (SED) of the most important (by intensity) backgrounds in the Universe, and their approximate brightness in nW m sr written in the boxes. Erom right to left the Cosmic Microwave Background (CMB), the Cosmic Infrared Background (CIB) tmd the Cosmic Optical Background (COB) [Credit Dole et al. A A, 451(2), 417-429,2006, reproduced with permission ESO]...

RE. Dewdney, P.J. HaU, R.T. Schilizzi, T.J.L.W. Lazio, The square kilometre array. Proc. IEEE 97(8), 1482-1496 (2009). ISSN 0018-9219. doi 10.1109/JPROC.2009.2021005 H. Dole, G. Lagache, J.-L. Puget, K.I. Caputi, N. Femandez-Conde, E. Le Floc h, C. Papovich, P.G. P6rez-Gonzalez, G.H. Rieke, M. Blaylock, The cosmic infrared background resolved by Spitzer. Astron. Astrophys. 451(2), 417-429 (2006). doi 10.1051/0004-6361 20054446 ESA Concurrent Design Facility. Far Infrared Interferometer—CDF Study Report. CDF-49(A) 1-294, (2006). http //sci.esa.int/future-missions-office/40738-firi-cdf-study-report/... 

At the Detector Noise Moduie, the Noise Equivalent Power (NEP) associated to the detectors and the 1 // noise are calculated. In parallel, with the physical properties of the system defined, the Background Power Module calculates the background power noise due to the instmment and the Cosmic Microwave Background (CMB), Cosmic Infrared Background (CIB) and Zodiacal Light. 

The measurement of the cosmic microwave background. Far infrared astronomers were the first to develop thermal detectors. Some of the resulting technologies, such as neutron transmutation doping (NTD) [3], have been transferred to particle detection sensors and have allowed many groups (e.g., ref. [4-11] to make rapid progress). 

We shall now describe an infrared bolometer operating at 0.3 K, built by Lange et al. in 1992 [80], We chose this example because such composite bolometer can be easily described from a cryogenic point of view, whereas the analysis of more recent devices would be quite complicated. Nevertheless the bolometer performances are very good, the NEP being less than 10-16 W/(Hz)1/2 and the time constant r = 11ms. It was used for the measurement of the cosmic microwave background (CMB) in an experiment on board of a stratospheric balloon [81]. 

On the last three decades, several space experiments with parts at very low temperatures have been flown. Among these, we mention IRAS (Infrared Astronomical Satellite) launched in 1983 (see Fig. 14.1), COBE (Cosmic Background Explorer) launched in 1989, ISO (Infrared Space Observatory) launched in 1995 and Astro-E (X-ray Observatory), launched in 2000 with instrumentation at 65 mK [35], Some cryogenic space missions are in the preparation or in final phase in Europe, USA and Japan. For example, ESA is going to fly Planck (for the mapping of the cosmic background radiation) and Herschel (called before FIRST Far Infrared and Submillimetre Telescope ) [36], These missions will carry experiments at 0.1 and 0.3 K respectively. 

The most accurate measurements of the CMB spectrum to date have come from the Far InfraRed Absolute Spectrophotometer (FIRAS) on the COsmic Background Explorer (COBE) (Boggess et al., 1992). In contradiction to its name, FIRAS was a fully differential spectrograph that only measured the difference between the sky and an internal reference source that was very nearly a blackbody. Figure 9.2 shows the interferograms observed by FIRAS for the sky and for the external calibrator (XC) at three different temperatures, all taken with the internal calibrator (IC) at 2.759 K. Data from the entire FIRAS dataset show that the rms deviation from a blackbody is only 50 parts per million of the peak Iv of the blackbody (Fixsen et al., 1996) and a recalibration of the thermometers on the external calibrator yield a blackbody temperature of... 

There is also considerable variety in the astronomical goals. Seven experiments are devoted primarily to far Infrared surveys, seven to measurements of the cosmic background radiation, four to high resolution mapping and photometry, one to measurement of diffuse emission in the near Infrared, five to solar brightness, polarization, and spectra, and one to planetary spectra,... 

The bottom of Fig. 4 shows another profound measurement by COBE. The far infrared absolute spectrophotometer (FIRAS) instrument on COBE measured the spectrum of the cosmic background radiation and found it to be an essentially perfect fit to a blackbody spectrum. The solid line in the figure is a theoretical perfect blackbody spectrum and the squares are the measurements. Any cosmological theory must be able to predict this remarkably perfect fit. These two measurements are among the most important observations ever made in infrared astronomy. 

COBE has produced some of the most dramatic scientific achievements in infrared astronomy. COBE measured the spectral shape of the cosmic background and found it to be a perfect blackbody spectrum at a temperature of 2.37 K. COBE also made the first observations of structure in the distribution of cosmic background radiation that are the probable first step in changes that produced the galaxies, stars, and planets we know today from the primordial smooth distribution of matter produced by the Big Bang. 

The DMR experiment utilized techniques more common to radio astronomy than infrared. The main part of the instrument consisted of sets of opposed antennas looking at different parts of the sky. These antennas looked for differential signals indicating different temperatures at different locations. FIRAS was a version of the FTS discussed earUer. It compared the spectral shape of the cosmic background radiation against the spectral shape of internal blackbody calibrators. The DIRBE instrument was more similar to standard infrared instruments than the other two COBE experiments. DIRBE used a suite of four different detector types to map out the sky at several infrared wavelengths. This instrument has contributed very important information on the contribution of various types of astronomical objects to the total background radiation in the universe. 

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