1 Introduction

CONFERENCE SUM1V1ARY B.E.J. Pagel 1 1 NORD/TA, Copenhagen, Denmark. Abstract Some highlights of the conference are noted and commented on, especially abundances and chemical evolution and some problems relating to the overall cosmic abundance of heavy elements. 1 Introduction A previous meeting on dwarf galaxies was held at OHP nearly 5 years ago. At that meeting there were two concluding summaries, one from an observational point of view by Paul Hodge and the other from a theoretical point of view by Donald Lynden-Bell, who ended the conference with a disquisition on anti-tank weapons. Several of the issues discussed at that meeting have also come up at this one, e.g. dark matter, star formation histories, chemical abundances, gas distribution and dynamics, clustering properties and environmental effects. Apart from 5 years' worth of advances in these and other relatively traditional fields , the most striking change at the present meeting is a dramatic advance in the cosmological con nection. resulting from the CF and AAT red-shift surveys, HST observations including the Hubble Deep Field and the detailed studies of interveningiabsorption-line systems in front of quasars. Red-shift surveys have shown that irregular star-forming galaxies are the ones having the strongest cosmological evolution at moderate red-shifts, but to what extent these can- be classed as dwarfs is controversial. The maintopics covered at this meetingwere: Statistical properties of local dwarfs, Intrinsic properties reievant to cosmoiogy, Properties at significant iook-back times, ivi odeis and theory and Prospects with new instrumentation. In this brief summary I can only comment briefly on what s�ruck me being some of the highlights. I thank Eva Grebel, Fran�ois Hammer and as Max Pettini for some additional comments and corrections to my spoken version. 481 2 Statistical properties of local dwarfs The local luminosity function turns up at faint magnitudes (Jonathan Loveday and Neil Tren tham), and this is confirmedby morphological classification in the HDF (Simon Driver), leaving the possibility that dwarf galaxies make a significant contribution to cosmic matter density, lim ited by the resulting contribution to intra-cluster light. The current star formation rate from theKISS H-a survey (John Salzer, Caryl Gronwall) is 0.013 hso M0 yr-1 Mpc-3, 1.7 times higher than the lower limit from the Madrid UCM survey (Jesus Gallego) that has been used as a benchmark in surveys of past SFRs. The new value is of order (1/2)h5l of the average SFR density over the history of the known universe. There could still be upward corrections for selection effects and dust-enshrouded starbursts. H I (Martin Zwaan, Steve Schneider, Lyle Hoffman) tracks visible galaxies very closely, most of it in large spirals, and has a cosmic abundance of about 1/6 of its value at red-shift 3 from DLA systems, consistent with cosmic evolution models like that of Pei & Fall in which the reduction in H I is ascribed to star formation. The H I mass function resembles the galaxy luminosity function. We were treated to some spectacular pictures (Hoffman, Eric Wilcots, Pierre-Alain Due). There are differences between the H I properties of BCGs on the one hand and dI and LSB galaxies on the other. H I envelopes of BCGs are denser and more regular, which makes it seem less likely that dls and LSBs are descendants of BCGs (Liese van Zee, Caroline Simpson, Claude Carignan) and the dark matter and surface brightness distributions are different (Gerhard Meurer). BCGs have bursting star formation,whereas dls have 'gasping' SF, i.e. periods of star formationseparated by quiescent intervals (Monica Tosi). The amount of fading of tidal dwarfs depends on the presence or absence of an old population; less than 50 per cent of tidal dwarfs are still around today (Uta Fritze von Alvensleben, Due). Molecules are present in dwarf galaxies, but CO is not a good tracer (Ulrich Klein, Chris Taylor). 3 Intrinsic properties related to cosmology The IMF appears to be universal with a Salpeter slope above about l.5M0 or so, but somewhat more top-heavy than usually assumed (Claus Leitherer). Claus recommended that, for such purposes as deducing SFRs from UV or emission-line intensites, one should use the Salpeter function with a lower cutoffat 1M0. As noted by Piero Madau and others, this means a lower SFR by mass by about a factor of 2 relative to what is deduced from the widely used lower cutoff at 0.1M0. Daniel Kunth gave a very interesting discussion of Ly-a, which can appear as an emission line, a P Cygni profile or a damped absorption line according to the velocity field, which in turn may depend on the stage of development of superbubbles caused by star formationin an extended H I halo. One of the high points of this meeting was the investigation of star formation histories. Eline Tolstoy gave a superb description of HR diagrams obtained with HST for nearby systems such as Sex A, Peg, GR 8 and Leo A and their interpretation and Eva Grebel gave us also an excellent overview of population boxes in dSph, dE and dl members of the Local Group. Robbie Dohm-Palmer used HST to trace the star formationhistory in space and time over-t he last 600 Myr in Sex A and GR 8 and found star-forming clumps moving back and forth across concentrations in H I. Infra-red and spectral data show that most BCGs and star-forming galaxies have an older underlying stellar population (Georges Comte, Livia Origlia, Regina Schulte-Ladbeck, Armando Gil de Paz), which is of course needed to account for their metallicities if the H II regions are 482 not entirely self-enriched. I Zw 18 can be modelled either with a previous burst 100 to 400 Myr ago (Alessandra Aloisi) or with low-level continuous star formationup to the current burst (Franc;;ois Legrand). An apparent exception is SBS 0335, where there is no evidence for star formation older than 30 Myr (Thuan), but this system is so like I Zw 18 that one wonders. Thuan found zero metallicity in H I, but a similar claim for I Zw 18 has gone away as a result of work by Liese van Zee. So is SBS 0335 unique in having a pristine HIenve lope? Yuri Izotov discussed abundances in BCGs, mainly fromthe Second Byurakan Survey (SBS). His and Thuan's derived primordial helium abundance of about 0.24 is probably basically cor rect because previous lower values for I Zw 18 were affected by underlying stellar absorption, as was confirmedat this meeting (Jorge Iglesias/Pepe Vilchez). This removes any conflict with Tytler's 'low' deuterium abundance in the frameworkof Big Bang nucleosynthesis. Izotov re ported an 0 /Fe ratio similar to that found in Galactic halo stars, indicating a stellar population that is young relative to SNia lifetimes, maybe of the order of 1 Gyr. This is not unexpected, but one may ask whether it is clear that all the iron in the H II regions is in the gas phase, since iron is depleted in the Orion Nebula. A converse effect has frequently been claimed for the young population of the Magellanic Clouds, but in this case the Fe/O ratio now seems to be close to solar (Bernard Pagel). From an apparent lack of scatter in N/O below 12 + log(O/H) = 7.9, Izotov deduces that primary nitrogen comes from massive stars that also produce oxygen. Francesca Matteucci argued for the same conclusion from one DLA system reported to have N/O > 1. However, we know from other DLA systems that N/O is generally low with a large scatter (Patrick Petitjean). From this I would rather suggest that primary nitrogen comes from intermediate mass stars with lifetimes of several hundred Myr, short enough to occupy periods between bursts in BCGs like I Zw 18, but long enough to lead to scatter in the DLA systems if these are very young. Izotov suggested corrections to C/O values reported in the literature leading to constant C / 0 at the lowest metallicites, but the various trends and corrections are the same within substantial error bars. A further interestingaspect of I Zw 18 is the presence of WR stars, discovered by Izotov and Thuan. Dan Schaerer discussed the implications for stellar mass loss rates at different metallicities, concluding that all existing estimates have to be more or less doubled, with implications for chemical yields and the ionization of the intergalactic medium. The metallicity-luminosity relation for irregular galaxies has a dispersion, possibly large (A. Maria Hidalgo Gamez), but there are uncertainties in the data, largely based on 'empirical' methods using strong lines (Grazyna Stasinska). Possibly tidal tail debris dwarfs could be recognized by excess abundance, above the norm, at a given luminosity (Uta Fritze). An important problem in the study of SFR history is the role of dust obscuration, discussed in a very nice presentation by Daniela Calzetti taking account of varying dust nature and geometry. Many starbursts are shrouded in dust and detectable only in the IR (Marc Sauvage), and some quite high values of the extragactic background at submm wavelengths have recently been reported fromDI RBE. Daniela concluded that currently adopted SFRsare underestimated by about a factor of 2. Dark matter continues with us (Taft Armandroff, Andi Burkert, Ky Lo, Gerhard Meurer, Rob Swaters) and the old results are largely confirmed. The new twists are a possible contribu tion from H2 (Lo) and the effect of tidal forces on dwarf spheroidals, especially the Sgr dwarf where the evidence for dark matter is greatly weakened (M.A.

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