An end and a new beginning

This blog will bear no further entries. Its sole purpose was to blog from the IAU meeting and we had fun writing it. Thanks to Ulrike and Jens for contributing.

But this is not the end of the story: We just started a new, more persistent blog called "Apparent Brightness". It has all the texts from here and will soon get new ones. Check it out!

J. Casares: Observational evidence for stellar-mass black holes

This is the opening review talk of Symposium 238 on Black Holes: from stars to galaxies asross the range of masses. This will be the last talk I listen to before I have to make my way to the airport, but Ulrike Heiter, a collegue from Uppsala who works on stellar atmospheres, said that she might write a few things from S239 about Convection that starts this afternoon and will go on for the rest of this week.

Now to the talk by Casares: X-ray binaries are believed to be a stellar-mass black hole oriting a normal star. From the study of the radial velocity shift, one can determine the orbital period of the system, and from additional information on the star and its mass and properties (inclination of the system), the mass of the black hole can be calculated. The first example for this was 30 years ago.

The reason why these systems shine in X-rays is that material streams from the "donor star" towards the BH and forms an accretion disk around it that gets hot enough to do that. Depending on the type of the donor star, the accretion disk may even be optically brigher than the star during an active phase.

The basic argument of course is, that when you find an object with a high mass that orbits closely with a star, but you cannot see it and physics tells you that there is no way to have such an object withstanding its own gravitational pull, it must be a black hole. However, the number of dynamically confirmed BHs is still quite low (~20).

Also the lack of pulses and X-ray bursts indicates that there is no hard surface onto which things can bounce.

So how many are there and what is the mass-spectrum? Extrapolating from the known numbers tells that there should be 1000 dormant X-ray Transients (i.e. binaries) in our galaxy (this fits with binary models), but from stellar evolution, there should be 10^8 BHs in the Milky Way, out of which only the tip of the iceberg can be seen as XRTs.

The 15 reliable mass estimates range from 4-15 solar masses with more objects on the low-mass end. The most massive ones seem to lie above the values predicted from stellar evolution (Fryer & Kalogera 1999), but we are talking small-number-statistics here (2 objects).

G. Tancredi: Activities of the Observatorio Astronomico Los Molinos, Uruguay

What can be done with a small telescope and a CCD-camera? Quite a lot. The speaker lists several projects that they do at their facility, including confirmation of near-earth objects, comet identification and photometry, asteroid photometry and astrometry. The common-day follow-up observations are valuable contributions to the scientific community and also attacking region in the sky that are rarely studied is a productive niche.

O. Alvarez: Planetario Habana: a cultural centre for science and technology

The funding for this planetarium came internationally (maybe from IAU, I did not get that) and they use it to build up a center for the teaching of science and technology in central Habana. It is integrated with the museums of the city and will promote astronomical knowledge to the public, including cosmology. Architecturally, the big sphere inside the building that will hold the planetarium represents the sun and there will be models of the other planets in the same scale.

Opening will be in the end of 2007.

An inportant comment was made, namely to get to ineract with the teachers and provide help for them and a special program that is different from the popular show. Many planetaria seem to have problems to keep a steady audience that is used to visually impressive films and shows.

P. Rosenzweig: Encounters with science at ULA, Vernezula: An Incetive for Learning

This is about a program to establish science on all levels of education in order to counteract the lack of interest in science and the deterioration in the learning of science. They provide well prepared personnel which can aid faculty members who want to improve things and they organise events ("Encounters with Science") for children at the school of science where an extra effort is made to fight the impression that science is hard and that scientists are heartless, boring people.

These events have many stands with experiments (with much voluntary work from students) and are very popular with several thousand participants and intensive media coverage. This initiative from the most western part of Venezuela has spread over many parts of the country and will soon be held for the seventh time.

J. Fierro: Astronomy for Teachers in Mexico

This talk is about basic education and with a wonderful metaphore (ape-mother teaching the use of tools) she points out the basic structure of learning which includes the natural interest of children and practical experiments.

The speaker was adressed by pre-school teachers with 650 questions of the children and there were books written about how to answer them. These books are very helpful for and popular among teachers. Several other books are presented and she throws a copy of each into the audience. :-)

In middle school, where pupils think more about sex than science, the curriculum is less on astronomy and more on social problems and there are books by the speaker where different issues are adressed in a popular but scientific way.

Finally, she stesses the importance of teachers and of finding good ways to teach, because education is the most important way to leave underdevelopment.

H. Levato: Formal Education in Astronomy in Latin America

The speaker starts with an overview over the countries and places, where astronomy can be studied both at undergraduate and at graduate level. The amount of activity and students scales with the size of the country. 90% of the 500 PhD students in astronomy are in Argentina, Brazil, Chile and Mexico.

There is an intermediate group of countries, where there is serious effort in astronomy, but it would take more resources to consolidate their astronomy programs. The largest number of countries however have seriuous deficiencies in that respect. The speaker also found a correlation between the astronomical effort and the reply-time to emails. :-)

Although there are many astronomical facilities in latin america, it is the people who write the papers and it often is manpower which is the limiting factor.

In a comment it was pointed out, that Venezuela probably should belong to the first group, which the speaker already had suggested, but with a question mark.

J. Ishitsuka: A new astronomical facility for Peru: transforming a 32m-antenna into a radio telescope

There are some big antennae around that are not used anymore, because communication has been replaced by other means. Making telescopes out of them requires expertise which not necessarily available. For this project in Peru, they collaborated with japanese astronomers.

The tansformation of this satellite communication antenna shall start radio astronomy in Peru, create radio anstronomers by gathering knowlege and of course promote international collaborations. The antenna is good enough to go up to 2.2 GHz and the site is high up, remote and has good conditions. The location on the globe also makes it interesting for Very Long Baseline Interferometry. They have a working reciever and are well underway.

S. Haque: The Caribbean view from the ground up

Intitially, the drop-down list in the registration form for this meeting did not contain Trinidad (the speaker's home) - this was corrected. With a country of one million inhabitants and two astronomers, they are approached from all sides of society, also religious, for information about calenders and the sky. There is an effort on online-teaching and there are popular events like "star-parties", however classical seminars are widely ignored.

Astronomy is in the primary school curriculum, voluntary student work is very important and at university level they have succeeded in sending students to internatonal winter schools and universities. Research has mainly been theoretical, but now also contains others, like astrobiology.

They have a 46cm telecope, mainly used for monitoring quasar variability.

R. Kochhar: Promoting astronomy in developing countries: a historical perspective

Is astronomy a "western astronomy"? There has been astronomy going on all over the world during mankind's history. The speaker tries to get attention to insensitivities that for example are written in the history section of textbooks. The "cultural perspective" should be taken more into accont.

J. Hearnshaw: A survey of published astronomical outputs of countries 1976-2005

I could not resist to return to the meeting anyway before I fly back to Sweden tonight. I was tempted by the Session about the "Virtual Observatory", but I guess one can find out about that on the web anyway.

Therefore, I am sitting in the Special Session 5 on "Astronomy for the Developing World" right now. I only got the last minutes of J. Heranshaws talk, but the summary contained the following:
- There are 1.39 astronomers per million population over the world.
- There are 9000 members in the IAU.
- The majority of papers is published by IAU members.
- 112 countries have no IAU members, but 3/4 of the world's population live in IAU member-countries.
- The GDP of a country correlates with the number of it's IAU members.
- It also correlates with the number of papers published.
- Since 2001, there has been a rapid increase in multi-national papers and large collaborations.

The Planet Issue

Below I commented on the link to this blog from Seed Magazine where they said that one could find out about Pluto being a planet or not in this blog. I wrote that I will not write about this issue at all because I find it unimportant. They now have even added a reply, correcting their "mistake". :-)

Maybe my choice of words was provocative, but for some reason, most of the links to this blog seem to be about these three lines and how bad they are. I will now list the major critics and adress them. Some wrote that:
1. I was a snobbish extra-galactic astronomer bashing planetary science.
2. I had forgotten where my money came from and that popularising is important.
3. Even if this topic may be unimportant, it attracts attention and all popular attention to astronomy (or the IAU) is good.
4. I should have written about it.

My replies:
1. This could not be further from the truth. Yes, this subject is quite remote from what I do myself, but finding out how the solar system came about is great science and with the discovery of extra-solar planets, this topic is deservedly becoming more and more popular among astronomers.

2. Of course it is! Popularising is immensely important and I think that every astronomer is aware of that. But isn't it somehow logical, that I try to do that in my own field? To justify that what I myself do is interesting and important? If that is not possible and unapplicable, I totally agree that planetary science is a popular topic. When I do popular shows at our old refractor I certainly do not point at feeble galaxies, but at the moon and the planets.

3. Now we come to the point where I disagree. Attention for astronomy is good, yes. The topic, if Pluto is a planet, and how to define a planet has gotten attention, yes. Does that make it good automatically? I think not and here is why: It is semantics and not science. It creates the (almost totally wrong) impression in the public that what astronomers do is sitting in committees and debate what a planet is. Is that what they are willing to give tax money for instead for new discoveries? I doubt it. In addition, it takes the media attention away from real science (including planetary, in case you missed point 1.) and I think I am far from the only one who feels misrepresented by this issue.

4. Must I write about everything? I think everyone has to make choices because you cannot cover all. I wrote about this meeting from my own perspective and the meaning was to give people a glimpse of what is going on here. I chose to ignore the "planet issue" and hope it became somehow clear why.

The second week

I just tried to convince a collegue, who will be here during the next week, to continue what I started. I've said it before: If you yourself are an astronomer at this meeting and are interested in blogging here, please drop me an email (thomas.marquart (at) astro.uu.se) and I'll add you to the list. The technical part is easy.

The end?

First of all, thanks to Jens, who also wrote some summaries during the last days and posted them below.

The poster session is over (I got some nice feedback from people), I have checked out and will soon meet the guy with whom I'll be staying over the week-end (with HC). This means the conference is over for me and I certainly enjoyed it.

During the week-end, I'll finally get to see Prague. There is a slight chance that I will attend some talks on Monday before I fly back to Sweden in the evening. If not, I will at least address some of the critics that I got for turning down the "planet issue" below.

It was fun to write this blog and it felt good that it at least got some attention. Thanks to all readers. At times it was more effort than I expected to simultaneously listen, get the major points and rephrase them in own words. I will have to read over all of it after a while to judge for myself if I succeeded or not.

Friday's star formation

I missed some talks in the morning, but sleep is important, too. I came in time for the last three talks of S237 on "Triggered Star Formation in a Turbulent ISM" and all three were interesting.

C. Norman was talking about his theoretical work on disk simulations and what struck me a little was that people have enough confidence in the simulations being a good approximation for the real world, to do physics with "observations" on the simulated world and derive properties and laws from there. Of course, this is tempting since one has complete control over the simulation and can get much better "data" than in the real world. There are tons of arguments and tests that reassure and convince people that this really works and, indeed, why should a program that implements a well-understood physical process fail, except for (also well-understood) limitations like resolution and other approximations. But still, if one could observe it, one would not need simulated data, so since we cannot, there is also a lack in testing the simulations to the real world.

Using the density distribution function of the ISM (log-normal except at very low densities) and a scaling relation for the critical density where SF sets in, Norman showed an alternative to the Schmitt-law (also called Kennicutt-law) that has a more shallow slope and flattens out at high gas surface densities. The observed slope then has to be understood by a change in SF-efficiency, which offset the model with respect to each other. Since the observed correlation is very tight, this would mean that also SFE correlates tighly with gas density.

The next speaker, M. Krumholtz, started from simple arguments to understand why SF is so inefficient in the sense that the SFR would be 50 higher (both in the Milky-Way and in extreme cases like Arp220) if all the molecular clouds that are present would collapse and form stars. I cannot reproduce the whole line of argument now, but he also used the density distribution (depending on mass and virial parameter) in the turbulent medium and integrated over the region above the critical value to get SFRs which fell into the observed regime. This could be tested, if the census of molecular clouds in nearby galaxies would stretch to smaller masses, by simply comparing the predicted SFR as derived from the molecular gas content with the observed one.

The last talk and summary of this symposium was given by B. Elmegreen and he again stressed the importance of turbulence for SF, instead of the older picture of monolithic collapse of a molecular cloud.

In the afternoon, there will be a "poster session", which basically means that everyone who has a poster, stands by it to answer the questions of the people coming by. The problem is that, although not all have posters, many do and one has to find the balance to also look at the other posters and talk to the author, but that won't work if they just do the same thing. Surprisingly, it always works out somehow anyway and I am happy that they scheduled this also for S235 for which no poster session was planned initially.

M. Hudson: "Downsizing" from the fossil record

This is the final talk of Symposium 235 on Galaxy Evolution, but there will be much more other things going on tomorrow that are worth writing about.

Downsizing was mentioned frequently during the last days and in the presented survey, red, emission-line-less cluster-galaxies are used to measure the "fossil record" of galaxies, i.e. the old stars. The thousands of spectra are sorted by velocity dispersion (a measure of the total mass) and stacked together to get high quality average spectra with many spectral features that can be analysed to get ages of the stellar population.

Tey find that the smaller galaxies have smaller ages, i.e. downsizing. The age-spread is much larger at low masses than at the high-mass end. There was no morphological selection but of course it is ellipical that dominate the sample. The S0-type galaxies are slightly younger than Es with the same sigma, but this trend is weaker than the trend with sigma itself.

Comparisons with the total dynamical mass (also using Sauron-data) there is little room for dark matter (25%).

The ages also correlate with environment, i.e. distance from cluster center (16% change). Again, this is not a strong trend. Metallicity does not show a trend, but alpha-enhancment does. The tilt of the distribution in a color-agnitude diagram comes half from ages, half from metallicity.

By calculating backward, how te CMD would have looked for these galaxies at some earlier time, they can be compared to CMDs at some redshift.

O. Gnedin: The formation of dwarf galaxies and small-scale problems of lambda-CDM

The Lambda-CDM cosmological model works very well in predicting large scale structure. It however predicts many more dwarf galaxies than are found. This is called the "missing satellite problem" and it is not just a few missing, but it should be ten times more.

The solution may be twofold: fist of all, only the more massive of satellite halos may be able to retain enough gas to form stars and thereby are seen by us. In addition, subhalos evaporate due to tidal forces, once they come close to "their" big galaxy. It has been known since long from studies of the Local Group that different types of dwarfs live at different radii from the large galaxies and there seems to be an evolutionary connection.

A new method of measuring the DM-halo of the Milky Way are hypervelocity stars that move at 500-1000 km/s with respect to us. They probably have been slingshotted by the black hole in the center of our galaxy. By following and calculating the paths of these stars, the shape of the DM-halo can be determined and according to CDM, it should be triaxial. This test will yield first results in a few years and it is a good test of predictions from lambda-cold-dark-matter cosmology, which is the widely accepted picture of our universe.

C. Conselice: Galaxy Interactions and Mergers at High Redshifts

When do galaxies merge? The merger fraction does evolve lowly up to z=1.2 but at around 2-3, 50% of all high-mass systems are mergers. The small ones again have only slightly higer merging rate. So at z=1 most of the high-mass objects were in place.

Using the same methodology to find mergers on numerically simulated data (with C. Mihos), they derive absolute merger rates (per volume) and a sharp drop after z=1 is found for all masses. A typical massive elliptical galaxy (today) will have undergone 3-5 major mergers since z=3.

A significant fraction (maybe the majority) of SF at z<1 is produced by interactions and mergers. I think this is last point is still debated and there have been contradicting results, e.g. showing that interactions dot not really increase SFR as much as one would think.

D. Elmegreen: Clumpy Galaxies in the Early Universe

By looking at the Hubble Ultra Deep Field (UDF), one can classify galaxies by how they look. The number of clumpy and irregular looking galaxies increases as one looks at further and further distances. Disk galaxies seem to disappear at a certain redshift and only thick disks are found.

Clumpy galaxies seem to be more frequent at high z and it is basically the large star forming regions that are seen there. These clumps should dissolve and could build up a normal spirals. Indeed the "clump clusters" share several properties, altough they are less massive. The scale height of "clump chains" is found to be 1kpc, which could be connected to forming a thick disk.

A usual problem here is that one looks with a fixed set of filters (opitcal in this case), but due to the redshift, one looks at different wavelenths inside the galaxy. In this case, one admittedly only sees the regions that actively form stars and a much smoother underlying population of older stars would not be seen.

R. Bouwens: Galaxies Buildup in the Frist 2 Gyr

UV-luminosity functions at z=4,5,6 are presented and no evolution is found at the low mass end and the slope is steep there (-1.75). However, at the high-mass end things get brighter with time. This is the opposite of downsizing that I wrote about yesterday.

Converting this to the Madau plot means that it peaks around z=4 and declines towards 5 and 6. This is heavily debated since the dust-correction at high z is fairly uncertain.

Going even further (z-J), they found 4 candidates of z~7-8 galaxies (Bouwens & Illingworth, Nature 2006).

T. Wilkind: Massive and old galaxies at z>5

If galaxies form hierarchically, i.e. big ones form by the merging of small ones, shouldn't big galaxies then appear rather late in the history of the universe? One cound think so, but would be mistaken. Tommy repots on their finding from last year of a massive galaxy at z=6.5 that is red in color and show no ongoing star formation at all.

Is the presence of such an object that has finished forming all its stars at so early times a threat to the lambda-CDM cosmological model? This first of all depends on how many of these really exist. They look in the K-selected GOODS-south sample and find 18 candidates out of which 5 had to be discarded as being something else.

So they have 13 galaxies at z>5 with over 10^11 solar masses in stars and no ongoing star formation (although 50% are detected in 24micron). Correcting this for completeness gives a rather high number density which indeed opposes the lamba-CDM paradigm (too many as compared to existing DM-halos at that time), unless these estimates are either flawed in redshift or stellar-mass-estimates.

M. Steinmetz: Cosmic Web - Simulations

The "Cosmic Web" is the structure that arises in cosmological simulations and that is also observed: the universe is clumpy and most of the matter is in huge filametary structures that are made of and connect galaxy clusters.

In simulations the control of the dark matter is much easier than normal matter since it only interacts by gravity. With normal matter, one needs recipies for handling star formation, hydrodynamics have to be taken into account.

Very important: he shows in simulations that a merger may actually look like a disk in kinematical data and he warns the people around Genzel who find "rotating disks" at high redshift. I have to find that movie/paper on the web.

Simulated disks nowadays however seem to fit nicely wit observed ones when it comes to angular momentum. A comparison of a merger with and without AGN feedback is shown and it helps in the sense that otherwise simulated galaxies are too centrally concetrated as compared to real ones.

To test if angular momentum is induced to disks by tidal torques from the cosmic web, it is possible to check the orientations of disks. Indeed there is a correlation between the large scale structure and the orientation of disk galaxies.

The Milky-Way dark matter halo seems to rotate with around 100 km/s as derived from halo star kinematics. But I might have gotten this part wrong. :-)

L. Portinari: Cosmological formation of disk galaxies and the Tully-Fischer relation

The Tully-Fischer relation (TFR) for disk galaxies relates the absolute luminosity to its rotation speed. The angular momentum in simulations however is difficult to match with observed values and this is most probably due to the simplified treatment of baryons and thereby, again, feedback.

The question if the disk forms from a cooling flow from hot gas (at virial temperature) or by cold accretion is adressed and X-ray observations can give important clues here. Birnmoim & Dekel 2003 found less than 10% of the expected amount of hot gas, so cold accretion might be favorable. Gas does not need to be heated to virial temperature and there can be cold gas accreting along filaments.

They found an offset in the TFR for certain models but it was hard to grasp which objects they were, but one solution is claimed to be dynamical friction, i.e. the galaxy rotates slower than it should for the same luminosity.

Portinari et al. 2006 look at the evolution of the TFR from z=1 and find no significant mass evolution, while the individual objects gets to almost twice its mass.

A. Shapley: Galaxy Formation in protoclusters at high redshift

Thousands of UV-selected galaxies at z>1.5 with spectroscopic confirmation from Keck. 25% contain AGN. From clustering length (4 Mpc) the DM halo mass is derived to roughly 10^11.5-12 solar masses and these objects are presumably the progenitors of nowadays ellipticals (by following halo-evolution in simulations).

The highest X-ray detected cluster is at z=1.45. The speaker and collaborators find protoclusters at z>2 also from UV and measure/find the overdenities (factor 7) in a redshift subslice. The galaxies there have double stellar mass than the ones outside the cluster. They find the morphologies not to fall on the Hubble sequence, but I wonder if they took into account that even normal galaxies look very different in different wavelenth, especially in rest-frame UV which the HST images were made in, if I got it right.

M. Franx: Properties of galaxies at z=2-3

Between z=2-3 presumably many galaxies build the bulk of their stars and one has to have control over sample properties and selection effects.

The authors and collaborators select galaxies in rest-frame optical which means deep NIR-imaging with VLT in that case (MUSYC-survey). They place a mass limit at 10^11 solar masses. At this massive end, the red galaxies dominate the population (77%) already at that time.

But these red galaxies are not "dead", but still show significant dusty star formation. In the U-V over V-J diagram, a large part of the population lies below the local population.

Clustering correlation length correlates with J-K color (Quadri et al. 2006) which means that redder galaxies ar emore clustered.

F. Walter: The first galaxies and AGN

Quasars are not found at very high redshift. The record holder has been at z=6.4 for quite an amount of time and at this redshift, the universe was about 870 Myr old.

A fun fact with redshifts is that you observe different wavelengths in objects when use use a certain wavelenth for observations. Because there is a large peak of emission from dust in the mid- and far-infrared, this gets shifted into the mm-rane at high redshifts and thereby, an object that is much further away may not appear fainter than a closer one at all.

Molecular emission has been detected to redshifts over 6 as well and of course only the highest concentrations can be detected at these large distances. One can get hold of the ionisations state of the IGM via the proximity effect, which presumably is due to a large ionised sphere (formation time=10^7 yr * neutral gas fraction) and lets emission a little blueward of the lyman-limit at the quasars redshift escape.

S. Silich: Super-massive star clusters: from superwinds to cooling catastrophe to the injected gas reprocessing

How quickly does the gas that is heated by the SSC cool? The larger the cluster the more radiative cooling (I did not understand why) and eventually there is a regime of "catastrophic cooling" where no equilibrium solution exists any more.

Studies in M82 which blows a huge bipolar wind perpendicular to the disk (pretty picture) show that .... I missed it because I fetched the link to the picture. :-)

G. Tenoio Tagle: On the negative feedback from SSC

Instead of acting positively, feedback cann be negative in the sense that SF is suppressed by the strong winds that go out from SSCs. The speaker shows simuations of the wind and radiation that makes its way through a region of dense clouds. Wherever there is a gap and the wind can break out, it blows a bubble of hot gas out of the galaxy.

P. Kroupa: Cluster Formation and Dissolution

In last talk it was mentioned that 90% of all clusters in the Antennae get disrupted immediately and onlt the big ones will survive anyway, because it's only them who have a deep enouhg own potential well to retain the stars.

The speaker starts with cluster formation and talk about the simulations by Bonnell et al. which I just recently had included in my talk for a course back home. The efficiency in cluster formation is below 40%, which means that more than 60% of the gas in the cluster volume does not go into stars. When this gas is removed by radiation from the massive stars, the cluster suddenly loses this mass, becomes super-virial and therefore the cluster stars move quickly to larger radii. The cluster not only evaporates, it "pops".

The speaker argues that the "popping" of clusters might even account for the thick disk of galaxies, but I dont't really believe that, because, if I remember correctly, it is more likely that it is the infall of dwarf galaxies that build up the thick disk. It was just commented on this in the question session: the velocity dispersion of a smal thing is always smaller than that of the ISM itself.

B. Whitmore: The life and death of star clusters

Stars generally form in clusters and in a starburst, there can be super-star-clusters (SSCs) that make the ones still forming in our Milky Way and also 30 Doradus in the LMC look rather pathetic.

The speaker talks about the clusters in the Antennae and by age dating them one can trace the different encounters of the two galaxies, during each of which SF is triggered. Maybe surprisingly, the kinematics over a cluster region seems to be smoothly rotating with small velocity dispersions. So one does not need high velocity "smashing in" of stuff, the increase of pressure seems to be enough.

Looking at different regions, it can be seen that around a massive older cluster, newer ones are found, the formation of which was triggered by the wind from the first one. This depends very much on density: if the wind has "free way" on one side, not much will happen there, but if it runs into some dense material, this gets compressed and can form new star clusters. This is what I meant yesterday by "positive feedback".

A major point that I should have mentioned is that what makes clusters so interesting to study, is that one can be sure that all the stars inside formed at the same time. So it is possible to just treat the as single objects and determine ages and other properties for each of them. And of course they are much brighter than a single star and can be studied at larger distances.

The IMF of SC is a power-law over many scales which means that low mass clusters are much more frequent than big ones. The speaker argues that there is no special "burst-mode" of star formation, but that the really big SSCs are just the tip of the whole IMF and it is only statistics that make this tip populated only in regions where you have a lot of star formation.

Taking Picture

Im sitting in S237 and someone just tries to motivate people to go the big hall during coffee break to take a picture of the S237 attendants in from of a bis IAU logo.

This will never work. :-)
Coffee breaks are sacred to people.

Social Events

There is a whole schedule of social events that are organized around the meeting, mainly it's sightseeing. I do not know when people find the time for this, but I would guess the ones during the week-end are the most popular.

I don't think, I'll join one of these and I am not even sure if I will make it to the concert on Friday evening since I have to move to a new place. You might have heard of the Hospitality Club, anyway, that's how I'm going to stay over the week-end before I fly back home on Monday.

I somehow doubt that someone will show up and take over this blog to report from the second half of the meeting next week, so I think this blog will close already tomorrow...

Thursday

This morning, S237 on "Triggered Star Formation" seems to be more interesting than S235 on galaxy evolution. On the one hand, it's a pity that potentially interesting sessions overlap. On the other hand, choice from a larger variety surely isn't bad.

The talks in S237 will be about star clusters.

Over and out

That's it for today. More to come tomorrow.

Time for food and some of the good czech beers.

F. Fraternali on "Gaseous haloes: linking galaxies to the IGM"

Spiral galaxies have lots of gas around them. And the space between galaxies is not totally empty either: there is the inter-galactic medium (IGM).

The speaker presents very deep radio observations of NGC891 and, not surprisingly, finds gas t large distances from the plane. They find filaments and small counter-rotating clouds. In another case (NGC2403) they see infall of gas in the position-velocity-diagram.

They model their observations assuming hydrostatic equilibrium and the things that not not fit yet, may be resolved, when the interaction of the cold gas with the hot halo gas is included.

The IGM that was in the title, was however not mentioned very much.

G.L. Granato on "Mutual Feedback between SF and nuclear activity"

More on feedback, but while the last talk was mainly about feedback from stars, there are also AGN, i.e. supermassive black holes (SMBH) in the centers of galaxies, that radiate very brightly, when mass falls into them.

There are beautiful simulations by Di Matteo and Springel from last year, where they compare the merging of two disk galaxies with and without feedback from the quasar and find it to differ significantly. Text, images and movies here.

The AGN feedback mechanism can at the same time explain the relation between the mass of the black hole and the bulge of the galaxy (because it's the feedback that shuts down both BH-growth and SF at the same time) and the quick reddening of galaxies because the decline in SF is so quick.

As in stellar feedback, it is not clear how exacly and how much of the engergy is deposited in the gas. Radiation pressure, heating and kinematical flows are the candidates.

Much SF promotes the formation of the SMBH by producing the seed black holes and also by pushing material into it. It takes around 500 Myr in Granatos models for the SMBH to form and feedback from it to kick in and have an effect on the surroundings, cleaning it from gas. This is what we see as quasars at high (but not highest) redshifts and this phase is rather short. What is left afterwards is a "red and dead" galaxy that does no longer form stars.

As main conclusion, Granato stresses the mutual link between SF and the AGN that has to be included into models. The comparisons of his models with observations were in impressive agreement, but I have no idea how many free parameters are fitted here. This was just answered in the question-session: it's around 6-7.

G. Hensler on "Feedback from Star Formation"

As mentioned before, the energy release from various sources (mainly stars and AGN) is called feedback and it can act positively, enhancing SF even more, or negatively by shutting down star formation (SF). To understand all this, one needs to understand how stars work and how the ISM behaves.

Feedback takes place at all scales, from small (e.g. HII regions) to large, for example global outflows from galaxies and galactic winds. By feedback, SF is self-regulated in the sense that little SF can trigger more SF, but once you get too much, positive turns into negative feedback, preventing further SF.

This self regulation manifests itself in the Schmitt-law (famous paper by Kennicutt), stating that SF is proportional to the surface density of the gas to the power of around 1.5. The Toomre-criterion must be fulfilled to have SF at all and this accounts for a cut-off of SF at low surface densities. This self-regulation comes automatically, even in simulations and the Schmitt-law is nicely reproduced.

The efficiency of SF, i.e. what fraction of gas is turned into stars, depends strongly on the density of the ISM and in starbursts both can be very high. One uncertainty in studying feedback is how much if the released energy (e.b. by stellar winds) is actually deposited in the ISM and how much escapes by radiation. The values for this effficiency vary between one percent and one permille.

a. van der Wel on "The IR Properties of Early-Type Galaxies at z=1"

The rest-frame K-band mass-to-light ratio has increased by a factor of three since z=1. The one for B even slightly more. Even though it's are early-type (elliptical) galaxies that are studied, there seems to be 10% of young stars (not sure if I heard that correctly) in the z=1 sample. There is however no obscured SF or contribution from AGN.

Dynamical mass estimates are fine at all redshifts, but if one does SED-fitting in the optical and the IR, the derrived masses are higher by a factor of two to three in the IR, as compared to optical. This has implications in how well we know the global stellar mass density and how it involves

C. Martin on "Galaxy Evolution with GALEX UV Surveys, Spitzer and SDSS"

This is not the same C. Martin as two talks ago. Then it was Crystal, now it's Chris. He argues that the blue part of the bimodal galaxy distribution (in the color-magnitude diagram) is not a "cloud" but a sequence that is only blown up bt the spread in age of the stellar population.

So how does a galaxy move from the blue to the red sequence? He showed models of transitional colors and mass fluxes between the two regions, but I did not really understand this.

From several samples of galaxies and by looking at the IR-excess, he finds that, as expected, the SFR in high-mass systems has declined a lot sinced z=1, however, it has remained constant over this time in low-mass systems. Again, this is evidence for downsizing.

Pictures

I found my lost USB-cable at the "lost & found" counter and therefore, there are some more pictures from yesterday afternoon in the gallery.

R. Terlevich on starbursts and downsizing

How does the evolution of galaxies depend on their mass? It's known that small galaxies seem to evolve slower than large ones. This is called downsizing and may seem counter-intuitive if one thinks that galaxies form hierarchically, but it is not. It simply stems from the fact that regions of higher density (like clusters) evolve quicker than low-density regions, where mergers are much less frequent.

Terlevich reconstructs the evolution of H-beta equivalent width from observations and finds a large discrepancy with models which he attributes to the fact that the continuum contains not only the newly formed stars, but also the old stars and thereby the whole star formation history.

Generally, he also finds that more luminous galaxies are older and that more metal-rich ones are older, too. No surprise here, but the correlation seems to be quite tight.

C. Martin on "Starburst Feedback"

With "feedback" all kinds of energy input is meant. Feedback mainly comes from supernovae and from active galactic nuclei (AGN), that can significantly dirsturb the interstellar medium of a galaxy and produce outflows.

Again, we talk about ULIRGS and the ones which have the U for "ultra-luminous" are indeed all mergers. Blue-shifted absorption lines show that these outflows really exist and move at several hundred km/s. Very interesting is one example where they find the wind over the whole galaxy, but it still rotates, which it should not. She explains this by the wind being driven by the whole disk, but I do not see how that should work right now.

These global winds can be driven both by a starburst and AGN, but the actual mass in the wind is weakly constrained. In addition, she claims that there is little evidence that AGN can provide enough energy to shut down star formation by removing the gas, a mechanism that is becoming more and more popular.

C. Cesarsky on "The role of LIRGS in galaxu evolution"

I shortly mentioned (U)LIRGS being associated with mergers before. They are very bright in the near and far-infrared and dust emission plays a major role here. Indeed, they must have been much more usual in the earlier universe, since the IR-background which is weak in the local universe, but reaches or even succeeds the optical background radiation at higher redshifts.

By counting galaxies in different wavelengths and at different z, one can determine how the galaxy population has changed over cosmic time. A strong evolution is found and LIRGS are found to be frequent enough to account for all of the IR-background radiation.

Not all of them are irregular: 36% of LIRGS are instead found to be disk-like galaxies. At the rate that LIRGS are forming stars, they would double their mass (in stars) in less than 1 Gyr. But they only do this temporarily (for about 100 Myr) in the LIRG phase. This phase can reoccur and each time about 5-10% of the stellar mass is added.

Catherine Cesarsky, by the way, is the director general of ESO.

Niveau

I just boldly claimed (last post) that communicating with the public is important and maybe even this blog is little contribution to that, or at least I would like to think so. Nevertheless, I am well aware that what I write here may sometimes be cryptic to non-astronomers. I am afraid this is unavoidable, because there is no way to write as much and at the same time write the background to make it publicly understandable. Writing popular science articles is hard work and I have little experience with it.

Anyway, I'd like to hear your feedback on how you perceive this blog, so please drop a comment.

Wandering

Leaving S237, I just had a quick look into S236 about "near-earth objects" and the speaker talked about "rotational fission". There is much more interesting science in those rocks that fly around in our solar system than one could guess, but these topics are probably as far from my field as you can get inside astronomy.

After that, I wanted to have a look into the special session on Astronomical Facilities of the Next Decade. This was held in a too little room and people were already standing by the entrance. I think the speaker talked about the Square Kilometer Array (SKA), but I immediately left again. You always hear things about the future main telescopes from several sources anyway and there is little you cannot find out from the corresponding websites.

I went on to a session about Communicating Astronomy with the Public which is an immensely important topic in my opinion. There were only 20 people present and I just bumped into the questions of the last talk before lunch. It must have been about some software that faciliates the creation of pretty images. The speaker was questioned from several attendants, why this plugin-software works with (expensive and proprietary) photoshop only and not with the free (and open source) alternative GIMP. Since their software will be open-source, too, they were confident, that some funding for a port to GIMP will be found. I liked that this point was stressed so strongly and I think it is fair to say that the astronomical community is well aware of open source and using it heavily.

Triggered Star Formation

I just went over to another hall, where the S237 on "Triggered Star Formation in a turbulent ISM" takes place. As far as I can see, this mainly contains studies in the Milky way and the Magellanic Clound, where one can get much more detailed information than in distant galaxies.

Righ tnow, it is H. Beuther speaking on "Physics and Chemistry of hot molecular cores". Observations of the well-known Orion nebula are presented and sub-mm data seems to show that there is no massive compact source in the hot core itself. Molecular lines are studied here, Methane seems to be important, and I suddenly realise, that although this field should be closely related to galaxy evolution, I have very little clue what is going on here.

I think I'll continue wandering...

J. Palous on the "Star-gas cycle in galaxies"

Stars form from gas. Big stars explode and throw out gas, thereby enriching the gas with heavy elements. The gas forms new stars. If you have many stars, they can blow winds out of galaxies.

I admit, I did not listen very carefully to this talk. :-)

M. Dopita on "Quiescent Star Formation throughout Cosmic Time"

Starbursts have been mentioned in previous postings here. But is there also a significant amount of quiet, non-bursting SF going on? If not today, has it been existing at earlier times?

The first stars that formed in the early universe have probably been very massive and quite different from todays stars, mainly because heavy elemets are needed to cool more efficiently and this is not in place before the first stars. The IR-background and also the neutrino flux are possible means of getting a hold on this remote epoch.

Different tracers of SF measure different things, e.g. UV-continuum (GALEX) picks up older SF-regions in galaxies than the emission lines (H-alpha, [OIII]), that trace the young HII-regions (2-5Myr). Again, the attenuation from dust cannot be stressed enough, especially in the densest regions.

At low redshift, the different SF-tracers seem to agree quite well. But it is known that SF has declined by an order of magnitude since z=1 and conditions have been quite different and local calibrations are not good any more. The specific SFR peaks between z=6 and z=1 and that is the time when galaxies are mainly assembled. High-z sub-mm galaxies are real global starbursts with extreme SF-rates of several thousand solar masses per year. These objects are on average 100 times more luminous than nowadays galaxies.

The question raised in the beginning was not overly much addressed, but one of the main conclusions is that SF was all but quiescent during cosmic history.

Making Choices

So called "Joint Discussions" and "Special Sessions" outside and in paralled to the large symposia start today, but it is not before tomorrow, that I (and many others, I suppose) will have a hard time to choose, what to listen to.

The organisers and chairmen have done a good job so far to keep the schedule. This is essential if one wants to switch between lecture halls and events without losing time. If you want, you can have a look into the Progam Book on the web, which is the same that we got here as paper copies on arrival, together with loads of material in a shoulder/laptop-bag.

About this blog

To answer the question that came up: I wrote earlier that this blog is temporary and of course it is in the sense that the meeting only happends during this and next week. There will be no more postings after the meeting, but there is no reason to dispublish this site. It can sit here as long as Blogger exists...

I also want to apologize for language or spelling errors in the texts. The talks are coming at fast rate and I just type away. I also have not yet found the time to answer questions that were raised in the comments - but I will eventually.

L. Tacconi on "Spatially resolved kinematics of z=2-3 galaxies"

When studying distant galaxies, their spectra are shifted redward. For example, the strong optical emission line H-alpha is shifted to the infrared when observing at reedshift of 2. Emission lines can be used to measure the movement of the gas in galaxies with the help of the Doppler-effect. If you now have an instrument that measures this at each point in a galaxy, i.e. if you have a spectrum at each pixel of your "image", you can study "velocity fields" of the kind that I also have on my poster.

SINFONI at the VLT is such an instrument, working in the IR. The speaker presents very nice kinematical data of these far-away (z=2) objects and it is impressive how fast progress is going in this field. They find the objects to rotate and having disturbed morphologies. This may be not really surprising. A paper by Tacconi and collaborators (Genzel et al. 2006) that will be published in Nature tomorrow, will show the finding of a very interesting case with very high-resolution data.

V. Charmandaris on the IR properties of Galaxies

Starbursts, that is episodal strong star formation, happens in regions wiith a lot of dust. It plays an important role in the whole process of star formation, but one of its properties is: it blocks light.

Well, optical light is obscured but by observing infrared wavelengths, one can look through the dust. The speaker reminds us of the beautiful studies in the Antennae galaxy, where the regions that are dark and invisible in an optical image are the brightes in the infrared.

IR-luminosity is nowadays quite well calibrated as an absolute measure of the star-formation-rate (SFR) and has become more popular (than for example the H-alpha-flux) since the upcome of many IR-instruments during the last decade. In the mid- and far-infrared, the dust istself stars to glow due to (almost) black-body emission and measuring the amount and the temperature of the dust in these wavelengths also contributes to the understanding of what is going on. As usual, it is all information together that gives the most complete picture.

(U)LIRGS are (ultra-)luminous-infrared-galaxies and you can guess why they are called this way. Arp220 is the most close-by of these rare objects and it is very well studied. ULIRGS are most likely to be a short phase during a merger event of two large galaxies when a lot of stars are formed.

Day Three

It is the third day and S235 on Galaxy Evolution continues.

A. Ferguson on "The Structure of Galaxies at Faint Levels"

Why does one want to look at the hard-to-study faint outskirts of galaxies? The stars in the halo of galaxies and tidal tails from dwarf galaxies give clues about how galaxies are built up. It is quite certain that large galaxies form hierarchically from smaller ones and since new star formation in the center makes relics harder to study, it is in the outer parts of the galaxies where one can look for evidence.

The amount and structure of tidal debris depends on the cosmological structrue, so modelling this with different parameters and comparing it to observations, can yield another test of lambda-CDM cosmology.

The problem is that this stuff is really faint and we are not talking about many stars. Only at surface brightness levels below 30 to 35 mag/arcsec^2, it shows up clearly, and these levels are rarely studied. The speaker presents a survey of the surroundings of M31 which shows a large stream of stars stretching to very large radii. While tidal streams indicate rather recent accretion events, but the stars coming from galaxies that have fallen in long ago have settled smothly into the halo.

Let me also mention that a collegue from Uppsala, Erik Zackrisson, studies the outskirts of Blue Compact Galaxies and finds a red excess in the near-infrared colors that is very hard to explain. Many explanations for this have been ruled out and what seems to be remaining is a bottom-heavy IMF, i.e. an unusually high number of small stars compared to big ones.

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.

Joinig

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).

M. Tosi on IZw18

The full title of the last of today's talk is Izw18, or the Picture of Dorian Gray: the more you watch it, the older it gets. This is again about the object mentioned in the last talk (and blog entry) and discusses the case of the best candidate of a "young galaxy" in the local universe, and thereby being a counterpart of what has happened earlier in the universe.

A possible explanation of the low metallicity of the interstellar gas is that winds from supernovae blow out the metal-enriched gas and thus rid IZw18 of the metals it has produced.

There are AGB-stars detected in Izw18 (partly by my supervisor G. Östlin) and therefore the age must be at least 500 Myr. In addition, other groups (Momany 2005) have found an RGB and thus lifting the age to 2 Gyr.

Tentative results by Tosi calibrate the distance to IZw18 more accurately, thereby fixing the y-axis of the HR-diagram and determining if it is AGB or RGB stars one has found. It seems that indeed stars with an age of 1.7Gyr or older have been found.

D. Kunth: "Are the most metal-poor galaxies young?"

This is interesting for myself since it relates to the galaxies I work with, Blue Compact Galaxies (BCGs). "Young" means that it forms its first generation of stars. Only two nearby galaxies with metallicity of around a 50th of the solar value are known: IZw18 and SBS0335-052, two BCGs.

But even if we trust the metallicity determinations, it remains the question if metallicity acts as an "arrow of time". Especially, a young galaxy does not need to have low metallicity since the gas may be preenriched during the denser early phases of the universe, where also SF was stronger.

In the luminosity-metallicity relation (more luminous galaxies are usually more metal-rich) the objets mentioned above fall out of the line, since the strong short burst of SF only boosts the luminosity, while the metallicity stays the same for a longer time, because intermediate-mass stars have not yet had time to release their metals.

The claim of these galaxies being young galaxies has been challenged many times and indeed, a weak old stellar population can be found in most of the galaxies, presumed to be "young".

E. Skillman on "Age-metallicity relations in Dwarfs"

How does the metallicity of stars in dwarf galaxies behave with their age? Simply measuring the age and the metallicity does sound straight forward, but is difficult to carry out. It is expected that stars produce metals and enrich the galaxy in metals, but does the expected enrichment from our knowledge of stars match with the observed values?

Calibrations from the LMC (Cole et al. 2005) show a quick increase in Fe/H in the beginning, but not big evolution during the last 5 Gyr. This of course depends on the star formation history and in the dwarf-spheroidal galaxy Leo I (or was it II?) which shows significant recent SF, the metallicity only went up after this. Enrichment that follows star formation is also found in local group dwarf-irregular galaxies.

Talking about the gas content is difficult, since the history of gas infall is not determinable, except by assuming that gas infall is correlated with the star formation rate.

C. Maraston on "Stellar population Models"

Stellar population models are made up from models of individual stars by summing up the spectra of a distribution of stars of the same age and doing this at different timesteps, taking into account the evolution and lifetime of each type of stars.

This means that different types of stars dominate the light at different times, e.g. it is RGB stars that account for the bulk of light in old populations. To get this modelling right, it has to be calibrated against globular clusters, the stars in which are known to have formed together at some point. An alternative to this approach is using the fuel consumption theorem.

Newer models that take more physics (delayed RGB-onset) into account make the agreement with the spectra of high-z better and arrive at younger ages and smaller masses for these objects. Still, the age determinations are very insecure in some cases.

G. Gilmore about "Population Models"

Gilmore reminds us that although previous speakers have talked about dry mergers and anti-hierarchical evolution, this certainly is not true for less massive systems. In addition, the secular evolution of bulges (pseudo-bulges) may not be the whole picture, since the Milky-way's (MW) pseudo-bulge has mainly old stars, as derived by their alpha-over-Fe ratio.

He goes on to talk about the main stellar populations: PopI in the thin disk, an intermediate Pop1.5 in the thick disk, PopII in the bulge and a not-yet detected PopIII of near-primordial stars. The thick disk is surprisingly homogeneous in element ratios which indicates a coherent build-up over a rather short timescale.

There is significant structure in the outer parts of the MW and recently several more streams are found around our galaxy, that origin from disrupted dwarf galaxies that are about to be "eaten up" and the model predictions for the different stellar populations are do not really match the observations.

R. de Grijs: "From nuclear clusters to halo globulars"

Star clusters as basic building blocks of galaxies. Most of SF is believed to happen in dense clusters. The initial mass function of stars is also believed to depend on the density of the environment.

Young clusters show a power-law distribution while old globulars show a gaussian, how come? He an collaborators did work on intermediate-age clusters in M82 and found a turnover at lower masses. So very many clusters must dissolve on a very short timescale in a very compact region - or the initial distribution was not a power-law.

Review Paper: de Grijs et al 2003 MNRAS 343, 1285
Newer stuff: Ma, de Grijs, et al. 2006

E. Taylor on "Star formation and the non-existence of dark galaxies

Do all DM halos have galaxies or can you somehow prevent star formation? Some galaxies form very little stars, but have much gas around them. HIPASS is a complete census of all neutral hydrogen over the sky and it found no dark galaxies.

But why do all galaxies form stars? Cooling is the key here. To cool further down than 10^4K you need H2 -cooling to get the temperature low enough to have disk-instabilities an initiate star formation. In their simulations they set up thngs to favor dark galaxies, but all but one of their models does not form stars and there is a minimal star-formation-rate (SFR) which in turn keeps the HI-could stable by heating it up again. This means star formation is self-regulated and it again boils down to the Schmitt-law of SF.

But the major point against dark galaxies still is the non-detection in HIPASS, where about 80 detections were expected.

W. Ho about "the relation between galaxy propteries and the dark matter halo"

Galaxies residein halos of dark matter (DM) which form from initial density fluctuations. They are believed to well understood since they only interact gravitationally and can be simulated. But how do galaxies form in DM halos? Does every DM halo have a galaxy? How many galaxies are there in large halos as in galaxy clusters?
How does the mass function of MD halos translate into the luminosity function of galaxies? They do not really match well, but the "conversion", i.e. the conditional luminosity function (CLF) can be well constrained by theory and observations. Clustering in dependance of mass also comes in here. He assumes this CLF to have a Schechter-form and one outcome is that the luminosity per halo mass is not linear at all.
Once having the CLF you can use it to derive other properties. For example that the most light comes from halos of round 10^12 solar masses, or that the halo-distribution of L-star galaxies can have a quite wide distribution in halo mass.

E. Ensellem on "Spheroids ages, knematics and BH-relation

He talked about a lot more but just this one point: The feedback from AGN is a nice way to shut-down star formation and to explain the BH-Bulge-mass relation. It goes also into explaining the bimodality of galaxies, but the physical motivation for this mechanism may not well be well-grounded yet.

Monday morning talks

This mornings talks were about scaling relations of galaxies and the formation of bulges and disks. SOme interesting points were raised, e.g. that the bimodality of galaxy distributions in a color-magnitude diagramm can rather be seen as a bimodality in Bulge-to-Dike ratio than in galaxy type itself. Should we finally abandon the Hubble "tuning-fork" of classification? (Talk by S. Driver)

Rather than catching up with the past talks, I will try some "live-blogging" from now on.

Arrival

So, we have arrived in Prague and stay 5 minutes by foot from the conference center which is quite a big thing. Many astronomical events happen simultaneously, but I mainly attend the Symposium 235 about Galaxy evolution. The lecture ahll is not the biggest one available, but easily fits the roughly 250 attendants. Have a look at the hall and the view from here over Prag at my first pictures. More to come...

Poster done

I finally got my own contribution (a poster) to the meeting done, and printed it in big format. Tomorrow, we'll fly to Prag. If you want to have a look, you can find it here (PDF, 3MB).

Link here, please!

Since this blog is by nature very short-lived, it needs to become known very quickly in order to have a readership that makes writing worthwhile for myself and potential other authors . Please link here, if you are interested in astronomy!

(There is no commercial interest and there will be no advertising)

Invitation: Blog here!

I hereby invite all attendees at the IAU General Assembly to join this blog and write about their impressions and thoughts during this meeting. This site would become much more interesting, if we could become a group of serveral people from different fields of astronomy that attend different parts of the conference.

I suppose the only practical mode of operation is that you have your own laptop and make use of the wireless network that is supposed to exist in the conference center. That is my own intention anyway.

To be able to write here, you simply write an email to me (tmarqar (at) astro.uu.se) and ask for invitation. Then you will get an email that lets you create an account at Blogger.com (if you do not already have one) and become added to this blog. Then you are ready to publish here.

Looking forward to your emails!

Mission Statement

This blog will be a temporary enterprise. I will attend the General Assembly of the International Astronomical Union that takes place in Prague, Czech Republic, from August 14 to 25, and blog from there.

It will be a big event with hundreds, if not thousands of astronomers that are spread over different symposia and sub-conferences. I will only participate during the first week and mainly listen to the talks in Symposium 235 which is dubbed "Galaxy Evolution across the Hubble Time".

The main focus of this blog will be on astronomical results and news and I expect much interesting stuff to happen at this meeting. Postings may or may not require some background in astronomy and will probably consist in short comments and summaries that are not meant to be self-contained and complete. There might as well be some notes and reminders for myself.

I shortly considered blogging anonymously, maybe to be able to tell my "real opinion" about speakers and presentations without the fear of negative consequences for my future life in astronomy. Then I realised that astronomers usually are reasonably good at taking critics, that I do not intend to scathe anyone anyway and that I have no problem taking the responsibility for what I say or write. :-)

Therefore, some quick facts about myself: My name is Thomas Marquart and I am enrolled as a PhD-student in the Galaxy Group at the Uppsala Astronomical Observatory in Sweden. Since this blog will not be about myself, this should suffice.