This meeting represents a solid endorsement of the Graduiertenkolleg (GK), in both its choice of science themes and its organization. When I was a first year graduate student, Bart Bok visited the University of Washington, and repeated over and over, "If you want to study star formation, study the Magellanic Clouds." At the time he was bemoaning the lack of a millimeter observing facility in the southern hemisphere - something which has been rectified. The expansion of the theme from the Magellanic Clouds to dwarf galaxies in general has allowed the work at Bonn and Bochum to reach an even larger audience.
Having attended an earlier meeting of the GK, I should state that my impressions are all very positive. The benefits of forming a concentration of studies shared between two university departments are obvious and impressive. The students have access to numerous first class facilities, faculty, and many other resources. In fact, one can say that the students have enhanced access to numerous facilities since the resources available through the GK help to make them more competitive for observing time.
When I attended the GK meeting in the Fall of 1995, I was impressed with the many ideas for new projects that students were then forming. Many of those projects have been completed and were presented at this meeting. Good science is being done. The GK experience has become an excellent platform from which to launch a career in astrophysics.
Simply because of my recent research activities, many of my impressions are grouped under the category of stellar populations. First among them is that the HST is an instrument ideally suited for stellar population studies. The leaps forward afforded by the vast improvement over ground based resolution has revolutionized our view of galaxies.
Nowhere is this more true than for the dwarf spheroidal galaxies. In the last decade, our views of these "simple" systems has changed enormously. The variety of star formation histories is still begging for a simple explanation. The kinematic studies of literally hundreds of stars (many now with multiple epochs) in most of the dSphs have continued to bear out Aaronson's bold claim that these are dark matter dominated systems. As spectra of individual stars provide detailed abundance analyses, we may still be in for more surprises.
I was very impressed by the degree of sophistication in treatment of color-magnitude-diagrams (CMDs) and the general agreement between independent groups. For example, the presentations by Aparicio and Gallart showed how the different features in the CMDs could be used in concert to place strong constraints on star formation histories reaching back to the earliests epochs. Tolstoy and Hopp independently studied HST data on VII Zw 403 and (1) came to very similar conclusions about basic properties and (2) agreed on the features in the CMD which were most difficult to fit with a range of reasonable models.
There was a great deal of attention paid to the detailed structure in the ISM and its origins. I will never again confuse the terms "bubbles", "super-bubbles", and "supergiant shells".
In the detailed H I imaging of the Magellanic Clouds, we are confronted with the problem of how best to deal with the high degree of complexity. Does it make sense to divide everything into categories of "holes" and "concentrations"? Perhaps it is pertinent to reflect back on the work that Hodge conducted for many decades, providing H II region luminosity functions (which also required making decisions about whether to divide features into components or combine features into single entities). We have seen that Oey has taken these H II region luminosity functions and used them to distinguish between "saturated" and "unsaturated" IMFs. While the analogy is not sound on a physical basis, I wonder that we may not see a similar understanding of the H I holes and concentrations in the future.
Concerning ISM structure, it is evident that x-ray observations are rapidly playing an increasing role in our understanding of the phase structure of the ISM. The x-ray images available today remind me of the H I images that were available a few decades ago. As the spatial and spectral resolution and sensitivity increase, important new insights are bound to come from this waveband.
Also, concerning the bubbles, I was disappointed that after presenting a detailed star formation history of the Sextans A dwarf, no one asked about the connection between the stellar population and the H I hole. I tried to check on this in preparing for this summary talk, but the limited field of view of the HST WFPC2 observations didn't allow for a clear answer. Recently, van Dyk has shown evidence from ground based data for a radial gradient in stellar ages that supports a wind blown bubble model for the central H I deficit.
Moving to galaxy scales, the numerical calculations presented by Mac Low were very impressive. There has been endless speculation concerning the effects of star formation on the ISM of dwarf galaxies, and, in particular, the ability of a galaxy to blow away all of its ISM. These new calculations appear to present a more realistic impression of what is possible and what is not.
This leads to the connected question of what is the H I that is frequently found in the vicinity of dwarf galaxies. I refer to this H I which is usually at similar velocity but disconnected from the normal velocity fields, as "floppy disks". Two alternative origins immediately come to mind. It could be that this material is tidal debris, left over from an interaction or a merger. Alternatively, this could be material which is primordial in nature and has not yet been incorporated into the galaxy. Within the limitations of available observing facilities, it is difficult to design an observational test which distinguishes these two possibilities. It is, however, a very important question.
Finally, I have to admit that one of the most remarkable things that I heard during the entire workshop was the story of Hunter's graduate school foreign language exam. To pass the exam, she was required to translate a scientific article written in German. In fact, she translated the article into Spanish. I was impressed not only with the demonstration of language skills, but the display of stubborn independence found in astronomers everywhere.
This presentation of my impressions was accompanied by a visual aid. Uli Klein asked me to reproduce it in my conference summary, so it appears here as Table 1.
| 1) | DH TR DE ES |
| 2) | MM P BO BIP |
| 3) | ET UH FSP |
| 4) | NO AA SA |
| 5) | XR HY |
| 6) | HST BF SPS |
| 7) | IBVC BSS |
| 8) | DS EBKS |
| 9) | A H&C LHR |
| 10) | NN RFP |
| 11) | FD TR PG |
The conference participants were treated to a trip to Köln, the highlight of which was a tour of the Dom. The Dom had recently experienced some refurbishing work, as evidenced by the many ton scaffold that was still hanging in the top of the church.
The following exercise occurred to me. What if that scaffold had fallen and crushed some of the workshop participants?
For this exercise, I assume the following cosmology: (1) there is a heaven, (2) there is a single deity, (3) when good people go to heaven the deity answers their questions, and (4) all astronomers are good. The purpose of the exercise is not to quibble with my assumed cosmology, but, rather, to imagine the questions of the deceased workshop participants as they enter heaven.
To kick off the proposed exercise, I tackled the question what if all of the invited review speakers were done in?
I started with Jay Gallagher. (The main reason for this was because I wasn't sure how this would go over and Jay had already left for Munich.) Jay's talk highlighted the degree of the interconnections between different studies and how observations of dwarf galaxies had impact on literally every major question in astronomy today. Actually, I think that Jay's question was very easy. He would ask "What are the answers to everyone else's questions?"
Mario Mateo's talk emphasized the sophistication of the measurements of the dark matter associated with dSphs and their complicated star formation histories. I imagine that he would be able to negotiate a second question and the two together would be "What is dark matter, really?" and "Concerning dwarf spheroidals, where did the gas go?"
Elias Brinks has always been fascinated with detailed images of the distribution of neutral hydrogen in galaxies. On one hand, the energetics of the holes can be explained by the presence of stellar clusters. On the other hand, few of the known holes have identifiable stellar populations in their interiors. Elias would ask "How are these holes formed?"
Deidre Hunter presented detailed observations of star formation on different scales. In one case, she pointed to a sequence of two generations of star formation and proposed that a third might be ready to occur. A theory of star formation should have predictive power, and thus, Deidre might ask "Is there going to be a third generation of star formation?"
You-Hua Chu presented detailed comparisons of the x-ray distributions and the gas kinematics in the Magellanic Clouds. She questioned the assumptions of pressure equilibrium. You-Hua would simply demand a complete picture of the multi-phase ISM in the Large Magellanic Cloud.
Jan Palous showed us, through numerical simulations, how ISM bubbles evolve. The calculations are simplified by taking advantage of certain symmetries. He would like to know if 2-dimensional simulations give the correct insight into a three dimensional world.
Trinh Thuan presented observations of SBS 0335-052, which he proposes is a young galaxy which is just forming now. He would like to know if it is possible for galaxies to be forming in the current epoch.
In summary, I would like to thank the organizers one last time for a truly enjoyable workshop. I congratulate them on their 25th GK meeting and I look forward to the 50th!
| First version: | 16th | September, | 1998 |
| Last update: | 23rd | September, | 1998 |