There were two plenary talks on the first day of NAM and both were pretty interesting. The first was by Richard Ellis and was about galaxy evolution. He described how our understanding of galaxy formation has suffered a bit of a set-back in recent years as heirarchical growth - growing big galaxies from small ones - has been challenged. Apparently massive galaxies can happily form at high redshift (big distances/early time) and smaller mass galaxies are continuing to grow at low redshifts (relatively nearby/late time).

He also told us about another problem in our understanding. We have measurements of the mass assembly history and the star formation history of galaxies but these don’t really seem to agree. Either there is too much star formation (not likely because we usually over-estimate) or we under-estimate the stellar mass. He suggested that there may have been a problem with the calibration of the data (likely) or there may be something about the universe we don’t yet know (unlikely, but would be interesting).

My favourite quote of the talk was that “a large fraction of massive galaxies are already red and dead by redshift 2 or 3.”

Richard posed the questions: Why do massive galaxies that form early on in the universe not really grow with time whereas smaller mass galaxies are still forming? What cuts off the star formation in massive galaxies? One answer may be that the radio jets from the central black hole stop cooling flow.

He mentioned that gravitational lensing surveys are being used to look for very faint and distant objects that have been greatly magnified. That means that we can look back to earlier times. Also, with adaptive optics on telescopes we can now observe galaxies with a resolution of 100 pc - that is around 326 light years - at a redshift of 3. That is a fairly impressive resolution.

The second plenary talk was by Don Pollacco on the search for exoplanets. As Don said, we live at a tremendous time in astronomy and although the UK was quite slow to join in the area of exoplanet discovery we are now fully involved. The talk started by giving a potted history of exoplanet discovery. The first exoplanet was found around a pulsar in 1991 and is still the only earth sized planet(s) known. The first exoplanet around a Sun-like star was found four years later in 1995. We are now up to around 270 known exoplanets.

Many of the early planets were found to be very close to their stars and that was a shock to astronomers who expected things to look much like our own solar system. It is thought that the planets have to form further out from the stars than we observe them so they must migrate inwards. Interestingly, a lot of the exoplanets have elliptical orbits and there are not many low metallicity stars with planets.  A plot was shown that compared simulations of planet formation (colour-coded by gas giant, icy planet or rocky planet) with the currently observed planets and it seems to show that we are mainly detecting the gas giant planets. Techniques such as gravitational microlensing will probably help find the smaller planets though.

Part of the talk was about the SuperWASP project, which Don works on, and which today announced the discovery of 10 new transiting planets. That is pretty impressive especially considering that only 35 had previously been discovered by the transit method.

Nick (The Jodcast) managed to record audio interviews with both speakers and we’ll try to post them on the NAM Blog tomorrow.