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Compter les galaxies infrarouges, raconter leur histoire : propriétés statistiques des galaxies infrarouges à grand redshift et origine du fond extragalactique infrarouge

Abstract : The extragalactic background light is the relic emission of the process of structure formation in the Universe. About half of this background, called cosmic infrared background, is emitted in the 8-1000 microns interval, peaks near 150 microns, and is essentially due to the star formation processes in the Universe. In fact, the infrared luminosity of a galaxy is linked to the hosted star formation. It is thus necessary to determine the evolution of infrared galaxies to well understand the origin of the cosmic infrared background.A rather simple statistical measurement, enabling to understand the origin of the cosmic infrared background, but also the evolution of the galaxies, consist in counting the sources as a function of their flux. I measured number counts of infrared galaxies using different methods in the data of the Spitzer and Herschel space telescopes, and of the BLAST experiment. The individually detected sources in the 24 microns Spitzer maps are responsible of the main part of the background. But, at larger wavelength, the sensitivity and the angular resolution of the instruments decreases, and the detected sources explain only a small part of the background. The stacking analysis enable to measure the mean far-infrared or sub-millimeter flux of a population detected only in the mid-infrared. This technique provides stringent lower limits on the level of the background, but also enables to count the sources which are too faint to be detected individually. These results are confirmed by the P(D) analysis, which determines the counts from the histogram of the infrared maps.These new measurements constrain the evolution of the infrared galaxies. I built a parametric evolution model to interpret the source counts. This model well reproduces the statistical properties of the infrared galaxies between 15 and 1100 microns. It predicts that the star formation in the young Universe (z>2) mainly happen in ultra-luminous infrared galaxies (LIR> 10^12 Lsun). These galaxies formed stars very quickly (more than 100 Msun/years), and have few equivalents in the local Universe. Nowadays, the star formation rate has decreased by a factor of ten, and the star formation mainly happen in galaxies like ours. This model has been used to interpret the fluctuations of the cosmic infrared background at large wavelength observed by BLAST, Planck, and Herschel.
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Submitted on : Wednesday, February 1, 2012 - 3:08:25 PM
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  • HAL Id : tel-00665256, version 1





Matthieu Bethermin. Compter les galaxies infrarouges, raconter leur histoire : propriétés statistiques des galaxies infrarouges à grand redshift et origine du fond extragalactique infrarouge. Autre. Université Paris Sud - Paris XI, 2011. Français. ⟨NNT : 2011PA112120⟩. ⟨tel-00665256⟩



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