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Dwarf Galaxies and Stellar Clusters Review Articles The MPA|ESO|MPE|USM 2008 Joint Astronomy Conference Supplement to The Messenger 134 December 2008 Garching bei München, Germany Chemical Evolution 21–25 July of Dwarf Galaxies and Stellar Clusters Review Articles Editors: Francesca Primas, Jeremy Walsh, Achim Weiss Conference Supplement Special Report on the MPA/ESO/MPE/USM 2008 Joint Astronomy Conference Chemical Evolution of Dwarf Galaxies and Stellar Clusters held in Garching bei München, Germany, 21–25 July 2008 Francesca Primas1 interesting and possibly helpful in under- small dark matter halos, which address Achim Weiss 2 standing the origin of the abundances in the ‘missing satellites problem’ and help both classes. to explain the detailed star formation histories of dwarf galaxies in the Local 1 ESO Indeed, the meeting turned out to be very Group. 2 Max-Planck-Institut für Astrophysik, lively and stimulating, with many interest- Garching, Germany ing new results presented. So many that All the presentations, including all the several review speakers mentioned that posters, are publicly available and linked their presentations, especially in terms from the conference website http://www. It is our pleasure to celebrate the success of number of known dwarf galaxies, were mpa-garching.mpg.de/mpa/conferences/ of our 2008 summer conference with the up-to-date ‘only’ until the week before garcon08/. This has also been a major publication of this special supplement the meeting, clearly demonstrating the accomplishment, and we would like to issue, in which we have collected the arti- incredible pace at which new ultra-faint thank all participants and presenters pub- cles of at least the majority of the review galaxies are being discovered from the licly for having been so responsive to ­­ talks presented at the meeting. Sloan Digital Sky Survey. our calls for papers and presentations. Special thanks go to the review speakers The 2008 MPA/ESO/MPE/USM Joint All the major areas were covered by who made it into this supplement issue. Astronomy Conference focused on the at least one review talk, followed by many We know that the deadline was very tight, chemical signatures and evolution of invited and contributed presentations. but our (now achieved) goal was to pub- dwarf galaxies and stellar clusters. It took This issue collects most of the review lish this supplement as close as possi- place in Garching at the end of July articles: from Mario Mateo’s opening talk, ble to the time of the conference. Finally, (21–25 July), and it was attended by 148 to Raffaele Gratton’s and Kim Venn’s our warm thanks go to all the students participants. There were no Proceedings, presentations on the chemical signa- and technical/admin istrative supporters as the Local Organising Committee had tures of globular clusters and dwarf gal- who have contributed to the success of decided to collect articles from the review axies respectively; to Santi Cassisi’s this meeting. speakers instead and have them pub- and Francesca D’Antona’s reviews on lished ‘somehow’ in the ESO Messenger. how these abundances can be inter- Enjoy the reading! This ‘somehow’ has now become a spe- preted in terms of stellar evolution models cial supplement to the December 2008 and how they could be connected; and Francesca and Achim issue of the ESO Messenger. last, but not least, the concluding remarks by Ken Freeman. The choice of the scientific topic of this year’s Joint Astronomy Conference in Further, at the meeting, Eva Grebel inves- Garching was driven by the current inten- tigated the links among ages, kinematics, sive work in determining stellar abun- metallicities and other properties of dwarf dances in galactic stellar systems (nota- galaxies and presented the dynamical bly globular clusters) and Local Group and chemical evolution of an isolated dwarf galaxies. Many of these projects system with the properties of a self-gravi- are being actively pursued with the latest tating three-component dwarf galaxy instruments, and have revealed surpris- consisting of gas, stars and dark matter. ing results. Abundances and kinematics Also, we heard a lot about the formation are now routinely measured for hundreds of stellar systems, in the nice reviews of stars per galaxy/cluster, thanks to given by Pavel Kroupa and Oleg Gnedin, the latest generation of multiplex facilities. the latter broadcast via video-connection Our mapping of the Local Group is basi- from Gnedin’s home institution. Kroupa cally changing on a month-to-month talked about the early evolution of dense basis (sometimes even more often), and stellar systems, its dependence on mass, the recent discovery of several ultra-faint and discussed some hitherto poorly dwarf galaxies clearly offers new horizons understood scaling relations in the transi- to explore. tion region between star clusters and dwarf galaxies. Gnedin presented an As globular clusters and dwarf galaxies overview of the dynamical evolution of form a mass sequence, and possible globular clusters and dwarf galaxies over connections between the two classes of cosmological timescales, with an empha- stellar systems have always been pro- sis on Local Group systems. He also posed (e.g., globular clusters as the cores described current ideas on the formation of former dwarf galaxies), a confronta- of massive star clusters in the first sev- tion and comparison of cluster and dwarf eral gigayears after the Big Bang, as well galaxy chemical evolution appeared to be as the latest models of star formation in 2 The Messenger 134 | Supplement – December 2008 Conference Supplement The Complex Evolution of Simple Systems Mario Mateo of the low luminosity end of the popula- galaxies, including the Milky Way. Dwarf University of Michigan, Ann Arbor, USA tion of spheroid systems (Figure 1 of Kor- galaxies and globular clusters must play mendy, 1985). In the past two and a half a central role in the hierarchical paradigm decades, we have come to realise that for a fundamental reason. These objects The simplicity and extreme ages of the simple appearance of dwarf spheroi- comprise the smallest and oldest sys- globular clusters and dwarf galaxies dal (dSph) galaxies belies a rich range tems surrounding present day galaxies. imply that these systems may be useful of population, kinematic, environmental But small and old things must, at the very windows to the earliest era of galaxy and chemical properties that are funda- least, be contemporaneous with the formation. Recent discoveries of local mentally at odds with the simple para- hierarchical ‘building blocks’ that we now dwarfs have, in some ways, begun to digm summarised above. More recently, believe drove the formation of larger blur the distinctions between the two some globular clusters – the very em- systems. Some of today’s systems may types of systems. However, it remains bodiment of simple stellar populations – even be identical to some of these early clear that the two types of systems have been observed to exhibit some structures, but, due to chance, have arose from fundamentally different con- bizarre properties that reveal unexpected not yet merged into larger galaxies. In ditions in the early Universe. Globular similarities to dwarf galaxies, blurring these respects, the local dwarfs and clusters result from ‘intense’ (what is the distinction between these two types globular clusters are identifiable fossils of often referred to as ‘efficient’) star for- of stellar systems. the era of active galaxy formation, an era mation processes, possibly related drastically unlike the present. Can we to major merging, while dwarf galaxies Even if we acknowledge that low lumi- interpret the messages that these fossils represent regions of much more ‘se- nosity spheroidal systems and their cous- contain? date’ (low efficiency) star formation, ins, the low luminosity dwarf irregular possibly independent of significant con- galaxies, are intriguing in their own right, This paper is based on my opening talk tributions from merging. I review spa- then it is their role in bigger questions at the very successful MPA/ESO/MPE/ tial, kinematic and chemical results that of structure formation that makes their USM conference, “Chemical Evolution of support this interpretation. study particularly compelling. Over the Dwarf Galaxies and Stellar Clusters”, course of my astronomical career – and, held in Garching in late July 2008 (and really, it has not been that long! – the skillfully organised by Achim Weiss and What could be simpler? Collect enough pendulum regarding the paradigm of gal- Francesca Primas, to whom I extend gas – and possibly dark matter – in one axy formation has swung completely my thanks). I thought that I knew enough region of space so that, even in the pres- from one extreme to the other. The mon- about both dwarf galaxies and globular ence of Universal expansion and a hot olithic model, first expounded in detail clusters to contrast their properties effec- cosmic background radiation field, it be- by Eggen, Lynden-Bell & Sandage et al. tively. Although there remain many funda- comes Jeans unstable. If dense enough, (1962), has swung to models that incor- mental differences between dwarfs and the cloud forms individual stars that ul- porate fundamentally hier archical proc- clusters that I outline below, the confer- timately settle into a dynamically quasi- esses, inspired by Searle & Zinn (1977), in ence did reveal some unexpected traits stable system in which the stars are dis- which small structures form first, then that they share. This may have muddied
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