Cosmic Horizons

Where did that month go? Winter is almost over and spring will be breaking, and my backlog of papers to comment on is getting longer and longer. So a quick post this morning on a recent cool paper by PhD student, Brendan McMonigal , called "Sailing under the Magellanic Clouds: A DECAm View of the Carina Dwarf". The title tells a lot of the story, but it all starts with a telescope with a big camera. The camera is DECam , the Dark Energy Camera located on the 4m CTIO telescope in Chile. This is what it looks like; It's not one CCD , but loads of them butted together allowing us to image a large chunk of sky. Over the next few years, this amazing camera will allow the Dark Energy Survey  which will hopefully reveal what is going on in the dark sector of the Universe , a place where Australia will play a key-role through OzDES . But one of the cool things is that we can use this superb facility to look at other things, and this is precisely what Bendan did...

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...

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...

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...

Science has been in the news over the last week, and it's been quite a successful research week for me. But while science has been in the news, I'm not 100% impressed by the way it has been presented. Firstly, there was  the lack of a dark matter detection by the Lux experiment . The reports around the web on this have been generally OK, but some have indicated that this is somehow a failure. But what is important, and is often not appreciated, is that in science the lack of a detection is as important as a detection. Negative results like this rule out possibilities and so are vital in cutting down the possibilities for what dark matter is. In fact, a lot of dark matter searches basically following the Holmes adage " eliminated the impossible, whatever remains,  however improbable , must be the truth ". Not seeing something increases our knowledge. The second made me a little unhappy. The article in question appeared in the Conversation and was titled " Is...

Back to research! And this week, it's a new paper from  Mark Fardal . Mark is an expert in modelling galaxy collisions, and we've been looking at the big collision going on next door, the  Giant Stellar Stream in Andromeda. One of the tough things to do is measure the mass of an object.  Measuring the mass of stars  is possible as long as it is orbiting another star, or has a planet orbiting it. Basically, the laws of gravity and motion given to us by  Isaac Newton  means that we can unravel the masses involved. However, measuring the mass of  galaxies  is much harder. Firstly, unlike stars, which can effectively be treated as point mass, the mass in galaxies is more complex. It is at its highest densities in the middle, but is roughly continuous, falling off as we head outwards. In this situation, using the laws of gravity and motion are messier to use. There is another, bigger problem. That is that the majority of the mass in a galaxy is...