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Dwarf Galaxies Europeon South.rn Ob.ervotory• ESO ML.2B~/~1 ~~t.· MAIN LIBRAKY ESO Libraries ,::;,q'-:;' ..-",("• .:: 114 ML l •I ~ -." "." I_I The First ESO/ESA Workshop on the Need for Coordinated Space and Ground-based Observations - DWARF GALAXIES Geneva, 12-13 May 1980 Report Edited by M. Tarenghi and K. Kjar - iii - INTRODUCTION The Space Telescope as a joint undertaking between NASA and ESA will provide the European community of astronomers with the opportunity to be active partners in a venture that, properly planned and performed, will mean a great leap forward in the science of astronomy and cosmology ­ in our understanding of the universe. The European share, however,.of at least 15% of the observing time with this instrumentation, if spread over all the European astrono­ mers, does not give a large amount of observing time to each individual scientist. Also, only well-planned co­ ordinated ground-based observations can guarantee success in interpreting the data and, indeed, in obtaining observ­ ing time on the Space Telescope. For these reasons, care­ ful planning and cooperation between different European groups in preparing Space Telescope observing proposals would be very essential. For these reasons, ESO and ESA have initiated a series of workshops on "The Need for Coordinated Space and Ground­ based Observations", each of which will be centred on a specific subject. The present workshop is the first in this series and the subject we have chosen is "Dwarf Galaxies". It was our belief that the dwarf galaxies would be objects eminently suited for exploration with the Space Telescope, and I think this is amply confirmed in these proceedings of the workshop. It is a pleasure for me to thank all the chairmen, who worked hard to prepare their sessions, and all the con­ tributing speakers. Per Olof Lindblad - v - EDITORS' NOTE Our appronctJ to the publication of this report has been similar tu that followed for previous ESO workshop and conference proceedings: the speakers were a;;ked to submit their manuscripts, which were then used directly for off­ set printjnff' We are grateful to the speakers for pro­ viding us with most of the papers shortly after the end of the workshop. The discussions after the papers are only printed when they were confirmerl in written form. We should like to express our grateful thanks to all those who helped us in the organization of this conference, in particular Renate van Doesburg. M. Tarenghi K. Kjar - vii - LIST OF PARTICIPANTS VAN AGT, S.L. Sterrenkundig Institut Toernooiveld NL-Nijmegen ALLOIN, D. ESO ARDEBERG, A. ESO ARP, H.C. ESO AUDOUZE, J. Institut d'Astrophysique du CNRS 98 bis, boulevard Arago F-75014 Paris BARBIERI, C. Istituto di Astronomia Vicolo Osservatorio 5 I-25100 Padova BERGERON, J. ESO BERTOLA, F. Osservatorio Astronomico Vicolo Osservatorio I-35100 Padova CASTELLANI, V. Istituto di Astrofisica Spaziale C. P. 67 I-00044 Frascati CRANE, P. ESO DANZIGER, J. ESO DENNEFELD, M. ESO DISNEY, M. Dept of Applied Mathematics and Astronomy University Colleget Cardiff P.O. Box 78 GB-Cardiff CF1 1XL D'ODORICO, S. ESO FEITZINGER, J. Astronomisches Institut Ruhr-Universitat Bochum Postfach 102148 D-4630 Bochum 1 GROSB~L, P. ESO - viii - HARTQUIST, T. University College London Dept of Physics and Astronomy Gower Street GB-London WCIE 6BT HUCHTMEIER, W.K. Max-Planck-Institut fur Radio­ astronomie Auf dem Hugel 69 D-5JOO Bonn JONES, B. University of Cambridge Institute of Astronomy Madingley Road GB-Cambridge, CBJ OHA KUNTH, D. ESO LAUSTSEN, S. Institute of Astronomy University of Aarhus DK-8000 Aarhus C LEQUEUX, J. Observatoire de Paris Section d'Astrophysique F-92190 Meudon LINDBLAD, P.O. ESO MACCHETTO, F. ESA/ESTEC Astronomy Division Domeinweg NL-Noordwijk MATERNE, J. Institut fur Astronomie und Astrophysik der TU Berlin Ernst-Reuter-Platz 7 D-l000 B~rlin 10 MELNICK, J. ESO NORMAN, C. Sterrewncht Leiden TIlly{~cns La-boratoriurn Wns~cnRnrsewee 7H NL-2100 RA Leiden PERRYMAN, M. ESA/ESTEC Astronomy Division Domeinweg­ NL-Noordwijk SA-NCISI, R. K~pteyn Astronomical Laboratory Hoogbouw W.S.N. Postbus 800 NL-Groningen - ix - SELLWOOD, J. ESO DI SEREGO, S. ESA/ESTEC Astronomy Division Domeinweg NL-Noordwijk 8HAW, R. ESO TAMMA~N, G. ESO TARENGHI, M. ESO TENORIO-TAGLE, G. ESO TERLEVICH, R. University of Cambridge Institute of Astronomy Madingley Road GB-Cambridge CB) ORA ULRICH, M.H. ESO VIALLEFOND, F. KapteYn Astronomical Laboratory Hoogbouw W.S.N. Postbus 800 NL-9700 AV Groningen VAN WOERDEN, H. KapteYn Astronomical Laboratory Hoogbouw W.S.N. Postbus 800 NL-9700 AV Groningen - xi CONTENTS Introduction "............. iii Editors r Note ....................................•• v List of Participants ................••......•..•••• vii Contents xi SURVEY OF DWARF GALAXIES (Session I; Chairman: G. Tammann) G.A. Tammann: A Survey of Dwarf Galaxies 3 J.V. Feitzinger: Galaxies of Magellanic Type: Preli- minary Report •••••••••••••.•••••••• 19 H. van Woerden: A Survey of Galaxies w~th Velocities Smaller than 3000 km s-1 •••••••••• 23 VARIABLK STARS IN DWARF GALAXIES (Session II; Chairman: S. Laustsen) S. van Agt: Variable Stars in Spheroidal Galaxies.. 33 S. Laustsen: Variable Stars in Dwarf Im Galaxies ••• 39 Im GALAXIES (Session III; Chairman: J. Lequeux) (a) Frequency Determination, Galaxy Luminosity Function G.A. Tammann: The Luminosity Function of Dwarf Galaxies 45 S. Laustsen and P. Gammelgaard: A Cloud of Dwarf Irregular Galaxies? ••••••••••••••• 49 (b) Hydrogen Content W.K. Huchtmeier: HI Content of Dwarf Galaxies •••••• 57 - xii - W.K. Huchtmeier: HI Observations of Irregular Galaxies 6S J. Materne: Envelopes of Late-type Dwarf Galaxies. 67 (c) The Magellanic Clouds J. Lequeux: Introductory Report ................... 79 J.V. Feitzinger: Studies of the Large Magellanic Cloud 83 A. Ardeberg, P. Linde, H. Lindgren and G. LyngR: Colour-Magnitude Diagrams and Luminosity Functions in the Magel- lanic Clouds 87 INTERGALACTIC HII REGIONS (Session IV; Chairman: D. Kunth) D. Kunth: Intergalactic HII Regions 95 S. D'Odorico, P. Patriarchi and M. Perinotto: Astrophysics of Galactic -and Extr~ galactic HII Regions with IUE: A Preliminary Discussion of the Car­ bon Abundance and the Absorption Line Spectrum •..••••.•.....•••... 103 C. Barbieri and D. Kunth: IUE Observations of Blue Compact Galaxies ••...•••....•.... 113 G. Statinska and D. Kunth: The Helium Abundance De­ termination in Emission-line Dwarf Galaxies 117 J. Lequeux and F. Viallefond: HI Observations and Star Formation in the Blue Compact Galaxy I Zw 18 •....••..••...•.•.• 121 G. Tenorio-Tagle: Isolated Extragalactic HII Re- gions. "The Triggering Mechanism." 123 J. Audouze: Theoretical Implications of a Low Helium Abundance in Dwarf Galaxies 129 - xiii - ELLIPTICAL DWARF GALAXIES (Ses~ion V; Chairman: L. Woltjer) (a) Chemical Abundances, Main Sequence Observations J. Danziger: Abundance Problems in Dwarf Spheroidals and Dwarf Ellipticals of the Local Group............................. 133 (b) Globular Clusters in Dwarf Galaxies V. Castellani: Globular Clusters in Dwarf Galaxies. 141 M.J. Disney: Are Some Dwarf Galaxies Crouching Giant s ? ........................•.. 1 51 F. Bertola: Energy Distribution in Dwarf and Giant Elliptical Galaxies ••.••..•••.•••• 161 MORPHOLOGY AND EVOLUTION OF DWARF GALAXIES (Session VI; Chairman: B.J.T. Jones) B.J.T. Jones: The Origin of Dwarf Galaxies •........ 167 C. Norman and B.J.T. Jones: Gas Rich Dwarfs •....•.• 173 T.W. Hartquist: Galaxy Formation by the Agglomera- tion of Primordial Star Clusters 175 J.V. Feitzinger: Stochastic Selfpropagating Star Formation in.Magellanic Type Galaxies.......................... 181 S. di Serego Alighieri: Summary of ST Capabilities on Dwarf Galaxies •..•.........•••• 183 - 1 - SESSION I (Chairman: G. Tammann) SURVEY OF DWARF GALAXIES 3 A SURVEY OF DWARF GALAXIES G. A. Tammann ESO; Astronomical Institute, University of Basel. Can the Space Telescope be used for a systematic search for dwarf galaxies? To answer this simple question, we should specify what we mean by dwarf galaxies, and consi- der some of their typical properties (or what we believe to be typical). I. Definition No unique distinction can be made between "normal" and "dwarf" galaxies on physical grounds. That is not to say that the possibility of a physical separation can presently be excluded. It could be, for instance, that dwarf and normal ellipticals obey separate luminosity functions, or that the space distribution of dwarfs is clumpier (or smoother??) than that of normal galaxies. All we can do for the moment is to propose a working de:finition; "Te will there:fore ca]l p,-a.laxles brighter than M B = m -16 "normal", and those fainter, "dwarfs." This definition excludes SMC (-17~0), but includes NGC 6822 (-15~3) and NGC 205 (-15~7) as dwarfs. The unfortunate, but unavoidable feature of this definition is that it depends on the adopted distance scale. For some Local Group (LG) dwarfs, the individual distances are still poorly known. For more distant dwarfs the luminosity depends on the preferred value 4 of the Hubble constant, which is taken here to be H = o 50 km s-l MPC-1 • m The one rational vindication of the limit of ~ = -16 may be that the luminosity function of dwarf irregulars seems to peak near this absolute magnitude (see Session Ill). For dwarf ellipticals, however, no turnover of the lumi- nosity function is observed, and their number -- at least in the Virgo cluster -- increases with decreasing luminosity. It would then seem that dwarf galaxies are more numer- ous than normal ones. That would bring astronomy hazardously close to psychology, where, too, the standard of "normal" seems frequently to be exemplified by only a minority. However, as Reaves (1967) has pointed out, the contribution of all dwarf galaxies to the total mass in the universe is dwarfish. Masses of galaxies being today notoriously uncertain, one would like to replace the param- eter mass by luminosity. Dwarf galaxies would then simply be that subset of all fainter galaxies, whose total contri- bution to the luminosity density (within a reasonably large volume) is negligible.
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