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Contenu gazeux et activité de formation stellaire dans les galaxies spirales isolées. Modélisation de l'émission infrarouge de la galaxie NGC6946.

Abstract : In this thesis we investigate the gaseous content and the star formation activity in the isolated disk- spiral galxies. In the first part, we present a study of a survey for 98 isolated spiral galaxies from the Karachenseva catalogue. CO(1-0) carbon monoxyde line observations of 98 isolated spirals have been macle with SEST, NRAO and IRAM radiotelescopes. 22 objects have been observed in HI 21 cm line with the Nancay radiotelescope. Observations of the Ha emission line for 65 isolated objects have been inade at Observatoire de Haute-Provence with the 120cm telescope. The isolated galaxies exhibit a lower CO(1-0) emission than the one deduced from previous surveys, biased towards FIR selection. Those objects show no HI deficiency. We evidence that the molecular to atomic gas mass ratio has a mean value 0.20: hence the molecular gas is not the main gaseous component of galaxy discs. This ratio decreases along the morphological sequence, except for the galaxies with high dynamical masses. This reference sample leads us to conclude that there is no CO deficiency in cluster galaxies, even when they are HI deficient. Classification of those objects according to their morphology in red band shows no significant difference betweeu grand-design and flocculent galaxies, barred or unbarred galaxies, as for their gaseous content, or their star formation ac-tivity. Principal components and multiple correspondance analysises enables us to evidence the relationship between infrared emission, molecular gaseous content and emission in the Halpha line or continuum in B band. Contrary to other studies, the content in atomic gas appears uncorrelated to the star formation activity. In the second part of this PHD thesis, we have developped a simulation code for radiative transfer of UV radiation in the spiral disk of the spiral galaxy NGC 6946. With this code including a small number of hypothesises, we are able to reproduce the far infrared luminosities for this object. We evidence the important role of massive stars in dust heating, and the large contribution of photodissociation regions to C+ line and far infrared continuum total luminosities. The luminosity ratio LC+/LFIR is small for atornic medium. We also evidence a low median opacity for UV photons for a galaxy seen edge-on.
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  • HAL Id : tel-00002684, version 2

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Sylvain Sauty. Contenu gazeux et activité de formation stellaire dans les galaxies spirales isolées. Modélisation de l'émission infrarouge de la galaxie NGC6946.. Astrophysique [astro-ph]. Université Pierre et Marie Curie - Paris VI, 1997. Français. ⟨tel-00002684v2⟩

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