The global star formation rate in high redshift galaxies, based on optical surveys, shows a strong peak at a redshift of z ∼ 1.5, which implies that we have already seen most of the formation. High redshift galaxies may, however, emit most of their energy at submillimeter wavelengths if they contain substantial amounts of dust. The dust would absorb the starlight and reradiate it as far-infrared light, which would be redshifted to the submillimeter range. Here we report a deep survey of two blank regions of sky performed at submillimeter wavelengths (450 and 850µm). If the sources we detect in the 850µm band are powered by star formation, then each must be converting more than 100 solar masses of gas per year into stars, which is larger than the maximum star formation rates inferred for most optically-selected galaxies. The total amount of high redshift star formation is essentially fixed by the level of background light, but where the peak occurs in redshift for the submillimeter is not yet established. However, the background light contribution from only the sources detected at 850µm is already comparable to that from the optically-selected sources. Establishing the main epoch of star formation will therefore require a combination of optical and submillimeter studies.In recent years high redshift optical galaxy searches have become increasingly successful at uncovering significant populations of galaxies that are likely to be in early phases of evolution. However, the global star formation rate (SFR) inferred 1, 3, 4 omits the many fainter sources that are now being detected. 5,6 Furthermore, the effects of dust can cause the SFRs in the detected UV-bright objects to be grossly underestimated (see, e.g., ref. 7), and many rapid star forming galaxies may even be omitted from the optical samples.Nearby star forming galaxies emit a large fraction of their bolometric luminosity in the far infrared waveband, which for distant sources is redshifted into the submillimeter waveband. Because the spectra of these star forming galaxies are very steep, if they are at large redshifts their flux density decreases much less rapidly with increasing redshift
Abstract. The mass absorption spectra of crystalline olivine particles with different Mg/(Mg + Fe) ratios, between forsterite (Mg 2 SiO 4 , Fo) and fayalite (Fe 2 SiO 4 , Fa), were measured for synthetic and natural samples in the mid-and far-infrared regions. The main strong peaks show a systematic shift to longer wavelengths as the Mg/(Mg + Fe) ratio decreases. In the 10-17 µm region, these trends are very clear, and the peak positions are a good indicator of the composition of dust grains. In the 20-100 µm region, the trends are also rather clear, though they are slightly complicated; the intensity and width of the various bands become weak and broad, respectively, or the bands disappear as the concentration of Fo decreases. However, the trends are clear only in a limited composition range near Fo and Fa; the peak positions of 30, 50, and 69 µm bands of forsterite shift linearly as the Fo concentration decreases to about Fo 70 . Those of the double band in the 50 µm region for Fe-rich olivine shift linearly as the Fa concentration increases from Fo 20 to Fa. When the spectral signature of Mg-rich or Fe-rich olivine can be observed, the peak positions in the 20-100 µm region are a good indicator of the composition of dust grains.
AKARI, the first Japanese satellite dedicated to infrared astronomy, was launched on 2006 February 21, and started observations in May of the same year. AKARI has a 68.5 cm cooled telescope, together with two focal-plane instruments, which survey the sky in six wavelength bands from mid–to far-infrared. The instruments also have a capability for imaging and spectroscopy in the wavelength range 2-180$\mu$m in the pointed observation mode, occasionally inserted into a continuous survey operation. The in-orbit cryogen lifetime is expected to be one and a half years. The All-Sky Survey will cover more than 90% of the whole sky with a higher spatial resolution and a wider wavelength coverage than that of the previous IRAS all-sky survey. Point-source catalogues of the All-Sky Survey will be released to the astronomical community. Pointed observations will be used for deep surveys of selected sky areas and systematic observations of important astronomical targets. These will become an additional future heritage of this mission.
The Far-Infrared Surveyor (FIS) is one of two focal plane instruments on the AKARI satellite. FIS has four photometric bands at 65, 90, 140, and 160 µm, and uses two kinds of array detectors. The FIS arrays and optics are designed to sweep the sky with high spatial resolution and redundancy. The actual scan width is more than eight arcmin, and the pixel pitch is matches the diffraction limit of the telescope. Derived point spread functions (PSFs) from observations of asteroids are similar to the optical model. Significant excesses, however, are clearly seen around tails of the PSFs, whose contributions are about 30% of the total power. All FIS functions are operating well in orbit, and its performance meets the laboratory characterizations, except for the two longer wavelength bands, which are not performing as well as characterized. Furthermore, the FIS has a spectroscopic capability using a Fourier transform spectrometer (FTS). Because the FTS takes advantage of the optics and detectors of the photometer, it can simultaneously make a spectral map. This paper summarizes the in-flight technical and operational performance of the FIS.
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