Cosmic Horizons

I am still playing catch up on papers, and I've just woken up early here in San Francisco and have a small amount of time before I have to prepare for my talk today. So, this will be quick. The topic again is our nearest largest companion, the Andromeda Galaxy, especially working out the history of how stars have formed in the (relatively) inner regions of the galaxy. It might seem a little strange that we can work that out, because all we can see is stars, but with the magic of science, it is possible. That's the topic of this new paper by postdoctoral researcher,  Edouard Bernard . This beautiful science is done with the Hubble Space Telescope. The first thing you need to do is decide where to look. So, here's the fields we looked at One of the sad things is that the area Hubble can image (its field of view) is tiny compared to the extent of Andromeda, and so we are doing key-hole surgery in select areas on interesting bits of Andromeda, especially prominent bits ...

Well, I don't know where that month vanished, but I now find myself sitting in the very nice  Swan's Hotel  in Victoria, Canada, after doing some nice new work with  Alan McConnachie  at the  Herzberg Institute of Astrophysics . The week has gone fast, and I've given two talks, and have four more to give in California next week. But I realised that I have neglected the blog, and there has been quite a few papers of mine put on the arxiv I should talk about. I have quite a bit of catching up to do, so here's a first post, and I will try and post some more over the next couple of weeks. A few weeks ago, I posted an article about the fact that we now have  the final catalog  of the globular clusters found in the PAndAS survey. This has been a major undertaking, seeing out these balls of a few million stars in the outer reaches of Andromeda. But it's been very successful, and we can now start to ask the question "what have we learnt?" This is the topi...

Back from an exhausting week in Canberra allocating grants for the Australian Research Council.  Handing out a few tens of millions of dollars really takes it our of you. The sad part is not the excellent projects we funded, but the many excellent projects we could not as we ran out of cash. Anyway, the meetings are confidential, so I can't discuss them here. But time to catch up on some of my own science. There is something super exciting coming, so here I'll focus on a merely excellent piece of work by globular cluster finder extraordinaire,   Avon Huxor  (excuse his ever so happy face!). I've written many times about the  Pan-Andromeda Archaeological Survey , our superb survey of our nearest neighbour, the  Andromeda Galaxy.  As well as identifying lots of substructure, the shredded remains of small galaxies, we also see lots of globular clusters, balls of roughly a million stars living together. The Milky Way has about a hundred of these orbiting i...

A cool paper this week, written by long-time collaborator,  Nicolas F. Martin . Again, it's a  PAndAS paper  but the focus is not Andromeda but our very own Milky Way. How, I hear you say. The starting point is the  Field of Streams , a truly wonderful image of a massive area of sky taken as part of the  Sloan Digital Sky Survey . Here it is The Sloan Survey had many goals, but one of those was to look at the stars in our own Galaxy, especially in the  Galactic Halo . If our picture of how galaxies form and grow are correct, basically by eating smaller systems, we should expect the halo to be full of the debris from things being consumed at the present time. And this is what we see in the Field of Streams. The big swoop across the image is the tidal debris from the  Sagittarius Dwarf Galaxy , which, even though it was only discovered in 1994, completely wraps the Galaxy. There's lots of other debris in there too, including the  Monoceros R...

Before we start, well done to the  Running Astronomer  on her most recent race. Papers are like buses. Well, their not really, but hot on the heels of yesterdays cosmology paper, another paper on the arxiv, this time with the friendly title of  A thousand shadows of Andromeda: rotating planes of satellites in the Millennium-II cosmological simulation . This is a cool paper and harks back to our discovery last year of the  discovery of a strange corotating plane of satellites  in the  Andromeda Galaxy . Well, here we are more than a year later, and there is still no satisfactory answer to what it is doing there (or the equally strange, and badly named,  Vast Polar Structure of the Milky Way ). Over the last few decades, we've built up a complex model for the formation and evolution of structure in the Universe, and the favourite picture, know as  ΛCDM , works extremely well on large scales. The Λ part refers to the influence of  d...

A quick post as I wait for the first coat of paint in the kid's bedrooms to dry. There's been a picture floating around on the interwebs showing a composite of the full Moon and the Andromeda Galaxy. Here it is. There is a discussion of this image over at  Bad Astronomy , and it's a composite of an image taken by  Stephen Rahn (over on flikr)  and an image of Andromeda taken by  GALEX , made by  Tom BH. Anyway, as you know, the disk of Andromeda is not all there is to the galaxy, and as part of the  Pan-Andromeda Archaeological Survey (PAndAS)  we've been mapping out the substructure into the halo of Andromeda. What if we plonked that on the above image? Well, I've done that and made the following (and credit to Stephen Rahn for the original image). How cool is that? It's an optical image of Andromeda itself on the same scale as in the GALEX image, but now I've also included the debris that we find in PAndAS. Just outside the main disk, t...

And now for a major paper from the  Pan-Andromeda Archaeological Survey (PAndAS) , led by astronomer-extraordinare  Rodrigo Ibata . I've written a lot about PAndAS over the years (or maybe a year and a bit I've been blogging here) and we've discovered an awful lot, but one of the key things we wanted to do is measure the size and shape of the  stellar halo  of the Andromeda Galaxy. The stellar halo is an interesting place. It's basically made up of the first generation of stars that formed in the dark matter halo in which the spiral galaxy of Andromeda was born, and the properties of the halo are a measure of the  formation history of the galaxy, something we can directly compare to our theoretical models. But there is always a spanner in the works, and in this case it is the fact that Andromeda, like the Milky Way, is a cannibal and has been eating smaller galaxies. These little galaxies get ripped apart by the gravitational pull of Andromeda, and their st...

Another week has flown by and I don't know where the time went. But another good week in terms of research with a new paper accepted. This one is led by postdoctoral researcher,  Nick Bate , with newly minted doctor,  Anthony Conn , and PhD student,  Brendan McMonigal . The focus of the study, substructure in the halo of the  Andromeda Galaxy  from, you guessed it, the rather fantastic  Pan-Andromeda Archaeological Survey (PAndAS).  The focus this time is a particularly prominent blob, known as the South-West Cloud (or, more colloquially to us, Japan). Here's a map of the substructure again. OK - I'll admit that the SW-Cloud doesn't look a lot like Japan, but the name stuck. As you can see, it's a reasonably big chunk of stuff, but we want to know what it is. And that's the focus of the present paper. This is my favourite picture from the paper, presenting the density of stars in and around the SW-Cloud. As you can see, it's a bit of ...

After a week of battling jet-lag, it's time to get back to some science. And this week, a new paper from the PAndAS , from Heidelberg based researcher,   Michelle Collins . The target here is  dwarf galaxies . Here's one from wikipedia. There's lots of dwarf galaxies out there in the Universe. In fact, in terms of number, they represent the dominant galaxies out there, but they are much smaller than our own Milky Way, so they don't have the dominant mass. Don't believe me? Well, my colleague,  Alan McConnachie , recently compiled the most comprehensive compilation of the galaxies within our  Local Group ; you can read the details  here.  So, we have three large galaxies, the Milky Way, Andromeda and  Triangulum , and then almost 100 smaller galaxies, a sea of dwarf galaxies. Now, you might think that dwarfs are simple things, just a billion or so stars living together in a dark matter halo, just a smaller version of large galaxies, but n...