Tuesday, August 15, 2006

Posters, not ceremonies

I just skipped the "Opening Ceremony" and the first Session of the general assembly itself. I guess I am not too much into ceremonial things and festivities. Instead, I went throught the poster hall and had both a discussion about my own poster and a look at some others.

Many have a pile of A4 copies at their poster board, so that one can take a copy if one is interested. Around 15 of mine have been taken so far, not too bad. I photographed those posters that interested me, but did not provide printouts. You can find them in the gallery with all other pics which is surprisingly empty, considering my usual rate of taking pictures.

Young Astronomer Lunch Debate

I just attended this lunch debate for young astronomers. Apart from the free food (some organisation from the USA paid), we were split up to many tables with different topics and had a nice discussion with senior astronomers. At my table it was 9 PhD studends and two seniors.

The topic was how to handle the large amount of papers that is published and if one should comply with the "publish or perish" attitude. We looked at statistics of refereed papers and there was a threefold increase in the last 30 years.

Obviously, we did not find a good solution for keeping up, because if there would be one, someone probably would have thought of it. We heard anecdotes from lost important papers that were rediscovered much later and thought that in the age of ADS and similar databases, things have become much easier.

One suggestion to get the number of papers down and at the same time make papers available for free and thereby disburden libraries all over the world was to put all the costs into the page charge of journals. These would be much higher then and could be scaled by the per capita income of the publishing country, in order to not disadvantage poorer ones.

I myself have been looking for a small tool to create an own index of the papers I have read. It must be able to handle "tags" to find a paper via several catch words. It should also to get the BibTex entry from ADS and at the same time know about the corresponding astro-ph page. Is there such a thing, or must I write it myself? Can't be too difficult...

There is a free afternoon now, and I will stroll through the poster area and have a look at some of them. In late afternoon, there will be a cocktail reception.

H. Ford on "Evolution of clusters from z=0.2 to 7"

This talk is on behalf of the ACS (one of the cameras on the HST) Instrumend Development Team. Galaxies at z=6 are presented and they seem to be irregularly shaped. There is an indication of luminosity evolution in the sense that glaies get twice as bright on average, when going from z=6 to z=3. They are also smaller and bluer at z=6.

There were many beutiful pictures from clusters shown, but I found it difficust to grad the overall picture, so I give up on this talk. :-)

Time for some coffe!

C. Mendes de Olivera on "Fossil and Compact Groups"

More than half of all galaxies come in groups, so does our Milky Way which resides in the ingeniously named "Local Group". But only a small fratction lives in compact groups. These groups are so close that they can share a common gas reservoir that has already merged while the optically visible galaxies still are individuals.

The most famous example is Stephan's Quintet and some details are given about it in this talk. In the tidal tails that are formed in interactions of galaxies, new dwarf galaxies can form and they are therefore called tidal-dwarf-galaxies.

She continues to present kinematical data from the same instrument that I used for "my galaxies" (CIGALE, a Marseille-based Fabry-Perot interferometer) and warns people to draw conclusions from long-slit spectra and low-resolution data from far-away galaxies, because the movements often show irreularities that only are revealed by 2D-velocity fields.

Seed gets it wrong

Seed magazine links here, but predicts that you will be able to find out if Pluto is a planet here. No, you won't! I think this is an incredibly unimportant topic, it's not what this meeting is about and I will not mention it at all. Well, not any more, that is.

B. Vollmer on "Galaxy Evolution in the Virgo Cluster"

How do Spiral galaxies evolve in clusters? Looking at the close-by (17 Mpc) Virgo with its huge central galaxy M87 reveals much detail. Clusters have many galaxies, so they are more likely to collide, but apart from this galaxy-galaxy interaction, there is the hot gas that fills the cluster potential and that exerts pressure onto the ISM of the galaxies moving through it - so called ram-pressure-stripping takes place.

Which of these interactions is more important? Polarized radio continuum emission gets stronger when the ISM is compressed, because the magnetic field is locked into it. This emission therefore traces compressions and shear. What Vollmer finds in a sample of galaxies, is that only one shows the normal signatures of field-spirals, while the others show distortions and excess emission on the leading side of the movement, thereby confirming that compression indeed takes place and that ram-pressure-stripping is efficient.

He also presents some simulations from different groups and they seem to agree (at least within a factor of two) with observations when plotting the stripping radius over the density of the medium. The general outcome thus seems to be a truncated disk, i.e. the galaxy can retain their gas inside a certain radius, depending on the strength of ram-pressure-stripping.

B. Moore on "Galaxy formation and transformation by environmental and secular processes"

Although galaxies are sometimes assumed to be "closed boxes", but in reality, they are not. Gas falls into them, it accretes, forms galacitc disks and there may be cooling flows. The latter have been proposed long ago, became unpopular for a while, because little evidence was found. Recently, they have been revived and Moore presents some evidence (recent papers by Kaufmann) for cooling flows.

In simulations, gas cools and forms a disk in an inside-out fashion. Unstable collapsing gas clounds form in the halo of surrounding hot gas and the study of angular momentum is an important method to distinguish different models.

When a small galaxy rich in neutral hydrogen moves through a region of hot gas, it can be stripped from its gas and leave a trail behind which falls onto the main galaxy. An example is the LMC circulating the Milky Way. Another one is spriral galaxies moving in the hot ICM of galaxy clusters.

If I understood correctly, he proposes that in less massive systems like polar ring galaxies, the main process is accretion of cold gas, while in more massive (L-star) ones, the gas is heated first and accrtetion by cooling is the more important.

He finished by "bashing" SPH simulations (quote: "they are pretty useless"), because they cannot capture certain instabilities that are important in a multi-phased medium. Grid-based simulations are preferable here.


Some visitors have found their way here, partly with the help of Phil Plait. If you are a fellow astronomer and are here in Prague as well, think about joining here and write some small articles. It's fun and actually helps you concentrating on the main points raised in talks. :-)

See the previous entry below on how to join here.

Second day starts

The fun thing about conferences is not only the science, it's also the evenings where you go out for dinner with people you have met during the day. Yesterday, I went with an Englishman, a Canadian, a Brazilian, a Swede and a Fin (Finlandian? Finnish?), so with me being German, we had a rather mixed group, although admittedly almost all of us did their PhDs either in the UK or Sweden.

The program for today is about what galaxies do, depending on "Environment and Interactions" and I again intend to do publish some summaries the second the speaker ends. During lunch, I will participate in a young astronomers lunch debate. There are no talk in S235 this afternoon, so I guess this is the time when people might have a look at some of the 1000 posters that are here (you can see mine here as pdf, 3MB).