Slowly cooking galaxies

Recent spectroscopic observations of IZw~18 have revealed homogeneous abundance throughout the galaxy and several observations of other starburst galaxies have shown no significant gradient or discontinuity in the abundance distributions within the HII regions. I thus concur with Tenorio-Tagle (1996) and Devost et al. (1997) that these observed abundance homogeneities cannot be produced by the material ejected from the stars formed in the current burst and result from a previous star formation episode. Metals ejected in the current burst of star formation remain most probably hidden in a hot phase and are undetectable using optical spectroscopy. Combining various observational facts, for instance the faint star formation rate observed in low surface brightness galaxies (van Zee et al., 1997), I propose that a low and continuous star formation rate occurring during quiescent phases between bursts is a non negligible source of new elements in the interstellar medium. Using a spectrophotometric and chemical evolution model for galaxies, I investigated the star formation history IZw~18. I demonstrate that the continuous star formation scenario reproduces all the observed parameters of IZw~18. I discuss the consequences of such a quiet star formation regime.Comment: Proceedings of the JENAM Conference (Toulouse, September 1999). To be published in New Astronomy Reviews, Editors Daniel Schaerer and Rosa Gonzalez Delgado. 8 pages, 3 figure

DG Affinity of DQ-modules

In this paper, we prove the dg affinity of formal deformation algebroid stacks over complex smooth algebraic varieties. For that purpose, we introduce the triangulated category of formal deformation modules which are cohomologically complete and whose associated graded module is quasi-coherent.Comment: 21 pages, references adde

Conformal covariance in 2d conformal and integrable models, in W-algebras and in their supersymmetric extensions

Conformal symmetry underlies the mathematical description of various two-dimensional integrable models (e.g. for their Lax representation, Poisson algebra, zero curvature representation,...) or of conformal models (for the anomalous Ward identities, operator product expansion, Krichever-Novikov algebra,...) and of W-algebras. Here, we review the construction of conformally covariant differential operators which allow to render the conformal covariance manifest. The N=1 and N=2 supersymmetric generalizations of these results are also indicated and it is shown that they involve nonstandard matrix formats of Lie superalgebras.Comment: Proceedings of the workshop "Supersymmetries and Quantum Symmetries" (SQS'99, Dubna, July 1999

A proof of Morse's theorem about the cancellation of critical points

In this note, we give a proof of the famous theorem of M. Morse dealing with the cancellation of a pair of non-degenerate critical points of a smooth function. Our proof consists of a reduction to the one-dimensional case where the question becomes easy to answer

Kinetic theory of a longitudinally expanding system

We use kinetic theory in order to study the role of quantum fluctuations in the isotropization of the pressure tensor in a system subject to fast longitudinal expansion, such as the matter produced in the early stages of a heavy ion collision.Comment: Proceedings of the POETIC 6 conference. 7 figures, 7 page