Professor Richard Ellis gave a plenary talk on galaxy evolution on Tuesday morning. We caught up with him to find out more.

MP3: Prof Richard Ellis Interview

I’m currently sitting in the Young Astronomers’ Session at NAM, coming to terms once again with the fact that I’m not really a young astronomer any more. Although PhD students present their work throughout the week, this is an extra opportunity to hear about the best work from a wide range of people.  As an example, the current speaker is Iraklis Konstantopoulous from UCL; it was inevitable I’d write about this topic because M82 is one of my favourite objects in the entire sky.  

 
M82 from HST (colour) and WIYN H-alpha showing galactic wind (pink)

As you can see, it’s an edge on spiral with lots of star formation, which is driving in turn the dramatic wind you can see. Iraklis & co have been studying star clusters in the galaxy; while they’re interesting in themselves they also contain information about the galaxy itself. For example, a large region of the galaxy appears to have fewer clusters than it should do.To understand this, you have to think about how M82 would look from elsewhere in the Universe. In fact, we have to consider what M82 would look like when viewed edge on. We need a galaxy with two prominent spiral arms, and a dominant bar. Rather like this one

NGC 1365 as seen by the Very Large Telescope

Now imagine viewing this galaxy from the bottom of the picture. On the right, you’ll see material ‘behind’ the spiral arm blocked by dust contained within the arm; hence the lack of clusters here. On the left, we see directly to the spiral arm, and this is where many clusters are found lurking. The best bit is that we can check this hypothesis by looking at the relative velocity of the clusters; and Iraklis does indeed find that clusters on the left are moving at a different speed to those on the right.The conclusion? Maybe M82 isn’t so weird after all…

You might think that with all the wonderful work astronomers have been doing in the last few decades, we’d know our local neighbourhood pretty well. However, Dan Zucker of the Institute of Astronomy took twenty minutes during one of the morning sessions today to introduce us to a few new neighbours. In 2003 we only knew of nine dwarf spheroidal galaxies, and even fewer around the Andromeda galaxy, far fewer than predicted by models of galaxy formation. In 2003 and 2004 several new galaxies were found in Sloan Digital Sky Survey data, alongside several streams of stars linking systems, but the level of complexity was still much less than that seen in computer simulations.

Astronomers turned to a more systematic technique, plotting the density of stars across the whole quarter (or so) of the sky that the SDSS data covers. As well as the streams of stars that were already known, a few small patches of the sky leapt out; lots of these were perfectly normal globular clusters, but others turned out to be new Milky Way satellites.

These are really faint systems, spread between 30 to 420 kpc away. Intriguingly, their stars are moving rapidly; the stars are moving so fast, in fact, that unless the galaxies are embedded in large haloes of dark matter they would quickly evaporate. The visible light we see would then be just the tip of the iceberg. Yet these galaxies are irregular in shape; normally, we’d attribute these irregularities to tidal interactions, but the gravitational pull of a massive halo should protect a system from this kind of disruption. These newly discovered next door neighbours have plenty more to teach us, it seems.

It must only be UK astronomers who associate NAM with meeting old friends and catching up on science rather than old war movies and Apocalypse Now, but at least this year’s National Astronomy Meeting is starting with a bang. An new image released by a team from our hosts, Queen’s University Belfast, shows a supernova in the galaxy NGC 2397.

The picture includes an image of supernova 2006bc, an explosion that marked the death of a massive star. Unusually, the image includes the supernova while it is still on the rapid climb to maximum brightness; capturing supernovae early is crucial to improving our understanding of these dramatic events. The work of the team at QUB focuses on combing through images taken before the explosion in order to determine the nature of the stars which will end their lives so dramatically. Their hard work seems to show that a stellar mass of just seven times that of the Sun is sufficient to produce such an explosion, but no very massive stars have been identified as supernova precursors. That suggests that these massive stars might be directly collapsing to black holes - an intriguing possibility.