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|The Star Formation History of the Universe: An Infrared Perspective|
A simple and versatile parameterized approach to star formation historyallows a quantitative investigation of constraints from far-infrared andsubmillimeter counts and background intensity measurements. The modelsinclude four spectral components: infrared cirrus (emission frominterstellar dust), an M82-like starburst, an Arp 220-like starburst,and an active galactic nucleus (AGN) dust torus. The 60 μm luminosityfunction is determined for each chosen rate of evolution using the PointSource Catalog Redshift Survey (PSCz) redshift data for 15,000 galaxies.The proportions of each spectral type as a function of 60 μmluminosity are chosen for consistency with IRAS and SCUBAcolor-luminosity relations, and with the fraction of AGNs as a functionof luminosity found in 12 μm samples. The luminosity function foreach component at any wavelength can then be calculated from the assumedspectral energy distributions (SEDs). With assumptions about the opticalSEDs corresponding to each component and, for the AGN component, anassumed dependence of the dust covering factor on luminosity, theoptical and near-infrared counts can be accurately modeled. High- andlow-mass stars are treated separately, since the former will trace therate of star formation, while the latter trace the cumulative integralof the star formation rate. A good fit to the observed counts at 0.44,2.2, 15, 60, 90, 175, and 850 μm can be found with pure luminosityevolution in all three cosmological models investigated:Ω0=1, Ω0=0.3 (Λ=0), andΩ0=0.3, Λ=0.7. All three models also give anacceptable fit to the integrated background spectrum. Selectedpredictions of the models, for example redshift distributions for eachcomponent at selected wavelengths and fluxes, are shown. The effect ofincluding an element of density evolution is also investigated. Thetotal mass-density of stars generated is consistent with that observed,in all three cosmological models.
|An image database. II. Catalogue between δ=-30deg and δ=70deg.|
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
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