Keele University

IAU Symposium 256

The Magellanic System: Stars, Gas, and Galaxies

28 July - 1 August 2008            Keele University (UK)

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Scientific Rationale

The Magellanic Clouds galaxies offer us a unique laboratory to study a wide range of astrophysical phenomena, from the birth and evolution of stars, through the physics of the multi-phase interstellar medium, to the dynamics and evolution of galaxies. At 50 kpc for the Large Magellanic Cloud (LMC) and 60 kpc for the Small Magellanic Cloud (SMC), the Magellanic Clouds are nearby satellites to the Milky Way galaxy. They are far enough that for many applications the extent of the Magellanic Clouds along the line-of-sight is not a serious factor, yet near enough that the three-dimensional structure of these dwarf galaxies can in actual fact be measured. Furthermore, their high galactic latitude allows an unobstructed view. As a consequence, many astrophysical processes are much easier studied in the Magellanic Clouds than in our own Galaxy. Many important breakthroughs in the history of astronomy have been made through observations in the Magellanic Clouds, such as the discovery by Henrietta Leavitt of the period-luminosity relation of Cepheid variable stars, or the detection by the Kamioka Nucleon Decay Experiment of neutrinos emitted in the supernova 1987A event. The Magellanic Clouds are being observed with essentially every new telescope or instrument that can physically access them, making possible stringent tests and calibration of theoretical models and driving much of our understanding of the Universe.

Although the Magellanic Clouds are small compared to spiral galaxies, they are among the larger examples in the class of irregular type galaxies, and studies of the dynamical processes occurring within the Magellanic Clouds inform us about the structure and evolution of dwarf galaxies as well as larger gas-rich galaxies such as the Milky Way. The Magellanic Clouds are interacting, both with each other and with the Galaxy, most clearly seen in the form of a trail of gas stretching out across half the sky (the Magellanic Stream) and a filament of gas and stars which extends from the SMC towards the LMC (the Magellanic Bridge). Thus, the whole of the Magellanic System also offers a unique opportunity to study in exquisite detail the interaction and assembly processes so prominent in the high-redshift Universe. With a metal abundance about a factor three (LMC) and eight (SMC) lower than that of the Sun, the Magellanic Clouds enable to study astrophysical processes as a function of the metal abundance. In particular the very metal-poor SMC allows to investigate processes in an environment typical of the formation of the types of galaxies that dominate the appearance of today's Universe. Hence, their proximity, activity and chemical differences make the Magellanic Clouds important templates for understanding galaxy evolution in general and the high-redshift Universe in particular.

With such diversity of astrophysical phenomena on offer, it is not surprising that four previous IAU Symposia have been organised on the Magellanic Clouds (#20, 108, 148 and 190), most recently the "New Views of the Magellanic Clouds" meeting in Canada, in 1998. Since then, high-resolution and sensitive observations and large surveys have been completed, continued or initiated, e.g., in X-rays with Chandra and XMM-Newton, spectroscopic surveys with 2dF, FLAMES and deep imaging with the Hubble Space Telescope, the MACHO and OGLE variability campaigns, the 2MASS and DENIS near-infrared surveys, the SAGE and S3MC infrared surveys with the Spitzer Space Telescope, the CO surveys with NANTEN, neutral hydrogen surveys at the ATNF and Arecibo, to name but a few. Recent studies in the Magellanic System have led to major advancements in many areas of astrophysics, including star formation and evolution, the physics of the interstellar medium and dark matter. Increasingly, highly sophisticated computer simulations help our understanding of these interacting galaxies in unprecedented detail.

Notwithstanding this, important questions remain, e.g.: how does the metal abundance influence star formation and stellar feedback; how does the structure of the multi-phase interstellar medium, from small to large scales, depend on its host galaxy; how has the interaction between the Magellanic Clouds and the Milky Way galaxy shaped their evolution? After ten years, it is thus timely to organise a new symposium on the Magellanic Clouds, Bridge and Stream, and to bring together the many astronomers who have studied the rich variety of phenomena in or surrounding the Magellanic Clouds, many of whom were only at the start of their careers a decade ago.

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