The Nature of the Low-Metallicity ISM in the Dwarf Galaxy NGC 1569

We are modeling the spectra of dwarf galaxies from infrared to submillimeter wavelengths to understand the nature of the various dust components in low-metallicity environments, which may be comparable to the ISM of galaxies in their early evolutionary state. The overall nature of the dust in these environments appears to differ from those of higher metallicity starbursting systems. Here, we present a study of one of our sample of dwarf galaxies, NGC 1569, which is a nearby, well-studied starbursting dwarf. Using ISOCAM, IRAS, ISOPHOT and SCUBA data with the Desert et al. (1990) model, we find consistency with little contribution from PAHs and Very Small Grains and a relative abundance of bigger colder grains, which dominate the FIR and submillimeter wavelengths. We are compelled to use 4 dust components, adding a very cold dust component, to reproduce the submillimetre excess of our observations.Comment: 4 pages, 4 postscript figures. Proceedings of "Infrared and Submillimeter Astronomy. An International Colloquium to Honor the Memory of Guy Serra" (2002

ISM Properties in Low-Metallicity Environments II. The Dust Spectral Energy Distribution of NGC 1569

We present new 450 and 850 microns SCUBA data of the dwarf galaxy NGC 1569. We construct the mid-infrared to millimeter SED of NGC 1569, using ISOCAM, ISOPHOT, IRAS, KAO, SCUBA and MAMBO data, and model the SED in order to explore the nature of the dust in low metallicity environments. The detailed modeling is performed in a self-consistent way, synthesizing the global ISRF of the galaxy using an evolutionary synthesis model with further constraints provided by the observed MIR ionic lines and a photoionisation model. Our results show that the dust properties are different in this low metallicity galaxy compared to other more metal rich galaxies. The results indicate a paucity of PAHs probably due to the destructive effects of the ISRF penetrating a clumpy environment and a size-segregation of grains where the emission is dominated by small grains of size ~3 nm, consistent with the idea of shocks having a dramatic effect on the dust properties in NGC 1569. A significant millimetre excess is present in the dust SED which can be explained by the presence of ubiquitous very cold dust (T = 5-7 K). This dust component accounts for 40 to 70 % of the total dust mass in the galaxy (1.6 - 3.4 10^5 Msol) and could be distributed in small clumps (size a few pc) throughout the galaxy. We find a gas-to-dust mass ratio of 740 - 1600, larger than that of the Galaxy and a dust-to-metals ratio of 1/4 to 1/7. We generate an extinction curve for NGC 1569, consistent with the modeled dust size distribution. This extinction curve has relatively steep FUV rise and smaller 2175 Angstroms bump, resembling the observed extinction curve of some regions in the Large Magellanic Cloud.Comment: 20 pages, 20 figures, accepted by A&

Louis-Philippe-Joseph, duc d'Orléans, Louise-Marie-Adélaïde de Bourbon et leurs deux enfants : [estampe]

Référence bibliographique : Hennin, 958

Prise de Saint-Omer, dans le grand escallier de Versailles : [estampe]

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Clara Schumann / C. Naumann del. ; W.C. Wrankmore sculpt

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Son Altesse - Royale Marie - Thérèse Charlotte - de France, Madame, Duchesse d'Angoulême : [estampe]

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Portrait de L. Duc de Bourgogne, enfant, couché sur son lit, dans une bordure ovale : [estampe]

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Le transport des filles de Joye à l'hôpital : [estampe]

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Portrait d'Angelo Constantini, en pied : [estampe]

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