Showing posts from 2012

Young accreted globular clusters in the outer halo of M31

Due to the Twilight Zone between Christmas and New Year, I am losing the catch-up game, but have just spent a rather wonderful couple of days up at Barrington Tops, camping in the wilderness and being "off the grid"; while I love camping, being off the grid is a rare situation for me. But that's not the story.

It's time to look at something I have written about before, and that is where did the globular clusters we see orbiting the Andromeda Galaxy come from? And as you might guess, this is another result drawn from the Pan-Andromeda Archaeological Survey (PAndAS).

This work is led by Dougal Mackey who is now at The Mount Stromlo Observatory in Canberra. Now, there are lots of globulars in Andromeda, most of them found close to the galaxy that is plain to see. What we have been doing in PAndAS is looking for the distant globulars, those far out in the faint stellar halo of the galaxy. Here's a picture from the paper
The underlying grey-scale is the density of sta…

Star talk slows chat

More alternative publishing success. This letter appeared in the Sydney Morning Herald just before Christmas
Being an astronomer and lecturer in relativity, I had to respond, and my letter was published today. Here it is
I wonder if this counts as the elusive "impact" that scientists will be judged on in the future? Anyway, the keen-eyed will see that a typo has crept into the text, as Tau Ceti is almost 12 light years away, not 120. I am sure there will be some smart-alec follow-up letters :)

Decelerating the Universe

It's Christmas day here in Sydney, and the rain has fallen incessantly; it feels like when I was growing up in Wales.

Anyway, I thought a short post. Over at In The Dark, Peter Coles was talking about the new results from the WMAP satellite, the latest of the probes of the Cosmic Microwave Background; I've mentioned before that I am old enough to remember the results from COBE, especially this front page story.
Basically, Peter's article points out that these observations have radically changed your understanding of the Universe. Mind you, looking at the above newspaper, and seeing "Bosnia ceasefire crumbles", tells me that in the same period, humans haven't advanced very far in the same period.

Anyway, in the comments, there was an interesting issue raised by Phillip Helbig (hi Phil!). Phillip and I are of the same vintage, and were raised on a diet of VMS before Unix became all pervasive in astronomy. Essentially, it is to do with the coincidence problem.


First Science with SAMI: A Serendipitously Discovered Galactic Wind in ESO 185-G031

Still playing catch up with papers, research, and just about everything at the moment. Even though my university has closed down for the Christmas break, work has not stopped (or even really slowed down that much), but I will try and fire off a few quick posts to at least get the papers out of the way. I also don't have too much time this morning, as I have to head to The Opera House to see this
Just for the kids of course!

I've written about the Sydney AAO Multi-Object Integral FIeld Spectrograph (SAMI) previously. Here's a bit on it that I pinched from James Allen's webpage on it.
The concept is simple (but the implementation is not). In the old days, we would do single-slit spectroscopy, where we would collect light from a distant galaxy through a narrow slit, and pass that through a disperser to get a spectrum. This would give us the details of what was going on along that slit (so we could measure rotation curves).
But this is slow. You can only look at one galaxy…

Paratrooper Speakers

Given that the Christmas period is upon us, but the rate of things to do has not declined, and people keep asking me if I have completed my Christmas shopping (no! and in truth, I haven't even started) time for a Scrooge-like post.

The following may upset my colleagues, so I will lay my card on the table. I am as guilty as the next person, but I am trying very hard not to be. I no longer want to be a Paratrooper Speaker. And I think my colleague should do the same.
Conferences, meetings and workshops have long been seen as an important aspect in astronomy (and a lot of academia). The chance to get together, hear some great talks discuss some good science, meet people and network. A chance for Early Career Researchers to meet some of those names on papers, and see just what is going on.

I am going to reminisce about the good old days, about conferences I went to when I was a student. Once, I got invited, after the conference dinner, to sit at the table with Geoffrey BurbidgeMarti…

PAndAS in the mist: The stellar and gaseous mass within the halos of M31 and M33

Time for another PAndAS papers (and yes, there are more to come!), but this one is from me :)

As you know, the Pan-Andromeda Archaeological Survey (PAndAS) is a big program we've been doing on the Canada-France-Hawaii Telescope, mapping out the locations of all the stars in the halo of Andromeda (M31) and Triangulum (M33) galaxies.

It's taken a lot of work, but with all the data now in, it's time to squeeze out the science. There is actually a bit of a hurry about this, as in the next year, we are making all of the data public, and even you can write PAndAS papers.

What's this current paper about? Well, let's start with the first picture in the paper.
So, the dense bits are M31 in the topish-right, and M33 in the bottom-left. The grey-scale is the density of stars in the map, and the regions outlined are the various bits of substructure orbiting around. Basically, there is a lot of stuff there, lots of streams, chunks, bits and pieces. Clearly, there has been a lot…

Alert: you may be living in a simulated universe

Today is a busy day, with the allocation of supercomputer time though ASTAC and the announcement of the 2012 Excellence in Research for Australia, which always leads to robust "discussion", and board of examiners meetings. So, only time for a quick post.

A new article in The Conversation on the controversial topic of "Are we living in a Synthetic Universe?". It's called Alert: you may be living in a simulated universe.

Given the comments, I could have alternatively called it "Baiting philosophers is easy and fun", but have a read yourself and let me know what you think.

Misunderstanding Peer Review

Sunday morning. I've got a busy week coming up, having to head to Canberra tomorrow for my induction into the Australian Research Council (ARC) College, then a few board of examiners meetings, the allocation of supercomputer time, and then Christmas drinkies on the Botany Lawn.

So a quick post on peer review.
There has been an awful lot written on this, and I will focus on academic peer review, especially when it comes to publications. I read this interesting article on peer review, which points out that the press does not seem to understand the difference between a published article, and things written in popular science magazines, on blogs, or simply chatted about down the pub.
But before I start, let me remind you how a paper gets published in a journal. 
It starts by you having your idea, doing your work, and deciding that the results are significant enough to be interesting to everyone else. 
You need to decide where you are going to publish it. Journals are tiered. There are…

Young accreted globular clusters in the outer halo of M31

I am still playing catch up on the papers I've recently had accepted, and after this one there are two more that I have to write up.

Today's paper is lead by Dougal Mackey at Mount Stromlo Observatory in Canberra (officially, its name is now The Research School of Astronomy and Astrophysics (RSAA), but it will always be Mount Stromlo to me).

The paper is yet another from the Pan-Andromeda Archaeological Survey (PAndAS), and so you know will be a cool result :). Dougal's expertise is globular clusters, balls of a few million stars that orbit large galaxies.

If we look at a nice globular in our own galaxy, it looks like this.
How beautiful is that?

However, the ones in the PAndAS images are 2 million light years away, and look something like this
Yes, those little balls of stars in the middle. Maybe a little less spectacular, but still extremely interesting. Why?

Well, the question we have is "Where do globular clusters come from?" Unlike other groups of stars we s…

‘Overmassive’ black hole holds the mass of 17 billion suns

A very quick post tonight. I was interviewed to comment on the discovery of a very massive black hole, much more massive than we would expect from the galaxy in which it is found.

This is a big black hole. Say it slowly... 17 billion times more massive than the Sun. That is a lot of mass in a very small volume.

The article is presented in The Conversation. You can read it here, and, as ever, I am happy to address any questions in the comments spot below.

Black holes. You have to love them!

Dynamics in the satellite system of Triangulum: Is AndXXII a dwarf satellite of M33?

I am playing serious catch up here, as we've had a wee flurry of papers accepted in the last few weeks, and I want to make sure they all get a mention. The good news is that I should have plenty to post over the Twilight Zone of the Christmas/New Year Period.

Today's paper takes us back to M33, and a bit of a curly question. As we've seen over recent papers, we've seen that the larger Andromeda Galaxy has a large population of dwarf galaxy companions, at least about 30 of them buzzing around (although not randomly, something I will come back to in the New Year).

M33 is about a tenth the size of Andromeda, and so we have the question "Does M33 have any dwarf galaxies of its very own?" This is actually a little complicated because M33 is in orbit about Andromeda, and passed near the larger galaxy a few billion years ago. It will do so again in a few more billion years.

Here's a map of the dwarf galaxies that we have found in the PAndAS survey, taken from th…

Kinematics of the stellar halo and the mass distribution of the Milky Way using BHB stars

I've been back for about a week, but it has been busy with a number of things.

Firstly, success in the current round Australian Research Council Discovery Projects. I'll write about this in a little more detail soon, but here's the summary.
There has been some uncertainty in the current round of funding, but it has all come out in the wash.

But there is more news. When I was traveling, PhD student, Parjwal Kafle, had his paper on measuring the mass distribution in the Milky Way.

This might strike you as a little odd. We live in the Milky Way, and it is the most studied galaxy in the entire Universe. Surely we know the mass of our own home galaxy? Don't we just add up all the stars we can see?

Well, if the stars were all there is, that would be correct. But we know there is more, much much more! There is dark matter, this stuff that dominates the gravitational attraction of the Universe. Our Sun is kept in its orbit by the halo of dark matter that surrounds the Galaxy.

On the good ship Volendam

I'm back! But where have I been? I've spent on 10 days on a cruise ship, the m/s Volendam. Here's what she looks like.
I wasn't just enjoying myself, I was there to lecture astronomy. The trip trundled from Darwin to Perth, calling in at the islands of Komodo and Lombok in Indonesia.

To pay my way, I had to give five lectures. I wasn't sure who the audience was (it turned out to be mainly people over 60, but from a range of nations), so I talked on
The Secret Lives of GalaxiesThe Big and Small of StarsHow to fall into a Black HoleJust what happened at the Start of the UniverseDark Energy and the Long Term Future of the Universe As well as me, there was also Victor Gostin of the University of Adelaide, who spoke on the geology and geophysics of South East Asia and Australia - did you know there was a now drowned continent called Sundaland (not to be confused with Sunderland!)? I didn't, and I think it was cool. Here's a map from wikipedia.
Anyway, I think tha…

Publishing Success!!!!

A very short post this week, as I am swamped - I will be away for almost 2 weeks and will explain in detail when I get back - but today was a good day in terms of my publishing.

Firstly, I got a letter accepted in the Sydney Morning Herald on science funding. Here's the letter.
But the bestest bit is that not only did I get the letter published (does this go on my CV), but I also got the letters' page cartoon dedicated to my letter.
I'm going to order a copy of the original cartoon to hang on my wall - I think it is excellent.

More when I have some more time.

Unearthing Foundations of a Cosmic Cathedral: Searching the Stars for M33's Halo

The Stellar Halo of a galaxy is a tenuous population of stars and other things surrounding the the bright spiral disk that characterises galaxies like our own Milky Way. Some of the oldest, most pristine, stars that we know can be found in the halo of our own galaxy, and so they provide clues to the processes that bought large galaxies into existence.

The problem is that they are, well, tenuous. When we look for halo stars in our own Milky Way, we have to sift through a sea of nearby fainter stars, to pick out the giant stars that are far away.

I've mentioned before about my work with the Pan-Andromeda Archaeological Survey, which has been mapping out the stars of our nearest large neighbours, the Andromeda and Triangulum galaxies.

Now that all the data is in, we're dissecting the various stellar populations in the vicinity of these tow galaxies, especially with regards to the large amount of substructure (the left over remnants of disrupted systems). But also we want to measu…

Catching the bus.....

OK, it's been a very good week (for reasons that will become clearer in the near future) and so I am going to take a breather for half an hour for a little recreational mathematics. The question is all about catching the bus.

One good thing about living in Sydney, which I've noted before, is that it easy to get to see international rugby at the Olympic Park. An excellent free bus service is provided to bring people in from the far-reaches of Sydney, and then take them home again.
It is quite impressive that it works, with tens of thousands of people pouring out of the grounds and onto buses quite efficiently.

So, I've been thinking - If people turn up at a bus stop at a certain rate, and buses arrive at a certain rate, then what do we expect the number of people on each bus to be?
OK, the question is easy if the people arrive at a fixed regular intervals, as do the buses. But we are not here to do the easy things.

Being a physicist, we start by simplifying the problem. Let…