Over and out
That's it for today. More to come tomorrow.
Time for food and some of the good czech beers.
Blogging from the International Astronomical Union Meeting, Prague, August 14 to 25, 2006
That's it for today. More to come tomorrow.
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).
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.
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.
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.
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.
I found my lost USB-cable at the "lost & found" counter and therefore, there are some more pictures from yesterday afternoon in the gallery.
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.
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.
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.
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.
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.
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.
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.
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?
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.
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...
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.
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.
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.