Happy New Year
New Year marked the start of night two of our observing run. We finished observing yesterday at just after midday – radio astronomers laugh at both sun and, in our case, cloud. The result’s weren’t great; we lost more than five hours completely to strong winds which might have been dangerous to the telescope, and the rest of the data was pretty shoddy. Not only that, but Daniel beat me soundly at first chess and then billiards.Tonight isn’t looking very good either – we’re struggling even to point the telescope at extremely bright objects – but I did at least join in with the Spanish tradition of eating twelve grapes in twelve seconds to welcome in the New Year. Let’s hope it brings us some luck.
A false start…
We’re off. Our first candidate galaxy is this rather nice system 
Before we can get to that though, we have to point the telescope at a well-known, bright source – usually an otherwise innocent and boring radio galaxy – to calibrate the system and to focus. Which is where our problems have started; the weather isn’t great (or is at least changeable) and we had trouble getting a decent focus. We ended up rotating the telescope by about 100 degrees to find a brighter standard source, and managed to focus. By the time we moved back to our galaxy, though, the wind had picked up and the telescope operator – whose concern is for the safety of the dish rather than for our observations – decided we had to stop.So we’re 90 minutes or so in, and have six minutes of useful data. It feels like it’s going to be one of those nights…
Hola from Pico Veleta
I’m sitting in what looks like a perfectly normal hotel room; bed, tv, shower and desk (with every astronomer’s essential needs – an internet connection – catered for). It’s only by opening the curtains that you might realise I’m somewhere special. Skiers are flying past in one direction, while in the other direction others are being pulled up the slopes on a chairlift. Down below the city of Granada stretches out in the foothills of the Sierra Nevada mountains. We’d worked our way through the throng earlier, looking incongruous pulling suitcases behind us among the multicoloured sportswear, on our way to use the IRAM SEO Services UK millimeter radio telescope. We’ll be looking at merging galaxies selected from the Galaxy Zoo catalogues, and then at some of the nearest blue ellipticals.IRAM is a hard working telescope – being a radio telescope we can observe right round the clock – and we’ve been allocated a shift from midnight to 12.30pm starting tonight. The skies are – at the minute – clear and so the lunch we just shared with the day crew and other observers has become dinner, and I’m off to bed. Daniel and I will be blogging throughout the run, so please do keep us company – we’ll have plenty of time to answer questions once things start running smoothly.
Getting Observing Time
If you followed the many interesting discoveries made by us all as part of the Galaxy Zoo team on the forum and the blog, you’ll have noticed that one of the most important things in astrophysics research is getting data. Unlike most other scientists, astrophysicists can’t just take a tiny galaxy into the lab and watch it evolve, perhaps feeding its (now tiny) supermassive black hole to see what happens. All we can do is observe the universe around us, and to do that, we need telescopes.
Observations are a bit like experiments. They are often designed to answer a very specific question. To take an example from Galaxy Zoo: when we first spotted the Voorwerp, and convinced ourselves that it’s real, rather than an artifact on the camera, we had to find out how far away it is by measuring its redshift and perhaps learn something about what it’s made of. To do this, we needed a spectrum, so we went about looking to obtain one. Normally, to get “time” on a telescope takes a lot of effort and waiting; in this case, we managed to convince some colleagues that the Voorwerp was exciting enough for them to forego some of their allocated time to take a peek at it.
So how do you normally get observing time? I’ll take the example of the XMM-Newton time we just got. Depending on the facility, the administrators will issue a “call for proposals” in certain intervals asking for proposals for observations. For most ground-based facilities, this will be twice a year. For many space missions, since they are harder to schedule, this may be only once a year, or even rarer. This “call” outlines the instruments of the facility, what kinds of proposals for time they will accept (lots of large proposals, no large proposals, etc.) and any technical issues proposers should be aware of.
We wanted to learn more about what physics the Voorwerp can teach us and one of the biggest questions about it is whether the supermassive black hole in IC 2497 (the spiral galaxy next to it) has really shut down, or if it is still a quasar and feeding. All indications so far are pointing towards a shutdown, but perhaps the quasar is really hidden by plenty of material in the way. So, we would like to use the X-ray vision of XMM-Newton, a 3.8 ton, bus-sized X-ray space telescope operated by the European Space Agency to take a look and see if any X-rays still get to us. Even if the quasar was highly obscured, some of the X-rays might still get through. It’s a bit like going to the doctor’s – we need an X-ray to diagnose what’s going on.
We thus sat down and wrote a proposal. The call for proposals outlines quite strictly how many pages, figures etc. you can use and what kind of information on the proposed observations they want. A proposal for observations generally consists of two parts: 1) a science justification and 2) a technical justification.
The science justification is an explanation of what you want to observe and what kind of physics you will learn from the observations. In our case, we described the discovery of the Voorwerp, how much excitement it generated with you all, and what we know about it so far. We then outlined precisely what we will learn with XMM-Newton data.
The technical justification following the science case is an explanation of why your proposed observations are really feasible. Will you really gather enough data to answer your question? Will the observations damage the telescope? Are there any other constraints? Are you (gasp!) asking for more time than you really need? All these are important. Even if you have the greatest science case, if you can’t make a convincing argument that your observations will work, you still won’t get time.
Preparing such a proposal is a lot of work. After submission (hopefully before the deadline!), the facility sends out the proposals to an anonymous panel for review (a bit like for scientific papers). This panel reads the proposals and meets somewhere for discussion. They assign each proposal a grade and so rank them. The telescope planners then approve proposals from the top until they’ve filled the available time. The remaining proposals are then rejected. This is actually the fate of most proposals. Popular facilities like XMM-Newton, Hubble or the VLTs are highly “oversubscribed”, regularly receiving five or even ten times more requests for observing time than they can give.
Astrophysicists thus spend a lot of time writing proposals in the knowledge that they’re unlikely to be accepted. Getting time is very precious and of course, every observation is an opportunity for discovery. As you can see from this description, it also takes a long time between applying for time, getting the time, and the actual observations. It’s fairly common to wait for your data for a year.
Luckily, so far Galaxy Zoo has been very successful with getting observing time….
4 Calling birds, 3 French hens, 2 Turtle Doves and 37,000 seconds of XMM-Newton Time
Just in time for the holidays, we got a little early Christmas present in our inbox. Applying for telescope time can be a large part of an astronomer’s work, and because astronomers often apply for far more time than is available, many worthy proposals don’t make it. If you’ve been following the blog, you know that in the past we were successful in getting time on facilities like Hubble, WIYN and IRAM to work on discoveries made by you all. So we were very happy to receive an email from esa confirming that we were awarded 37,000 seconds (or, in X-ray astronomer lingo 37 ksec) on the XMM-Newton space telescope.
Artist impression of XMM-Newton in space (from esa)
The title of our accepted program is: “How fast can an AGN shut down? XMM-Newton observation of IC 2497“. It’s with the piercing X-ray eyes of XMM–Newton that we hope to better understand the mystery Voorwerp. Just like at your doctor’s, X-rays in space can be a great tool to diagnose what’s going, in this case a supermassive black hole. One of the Big Questions about the Voorwerp is whether the quasar in IC 2497 (the spiral galaxy next to it) has really shut down, or whether it’s just hidden (obscured) by lots of gas and dust around it. With the help of this X-ray observation, we will hopefully be able to tell the difference between these two scenarios. When supermassive black holes feed, they emit radiation at many wavelengths, but X-rays are the most reliable measure of just how much material they really are gobbling up. The interpretation isn’t necessarily straightforward, as even X-rays can be blocked if there’s enough material in the way, but in 37 ksec (or just over 10 hours) with XMM-Newton, we should be able to tell the difference and make another step towards understanding what the Voorwerp really tells us about astrophysics.
So when do we get the data? As with all observations, it might take a while. The next cycle of observations lasts from May 2009 to April 2010…
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Update: A nice artist’s impression by Adrianus V from the forum :
Blue Sky and Red Spirals
This post is from Karen Masters at Portsmouth, who is working on red spirals….
When light travels through stuff it is scattered and absorbed. This is true of light passing through our atmosphere, and it is also true of light as it passes through galaxies. Light of different wavelengths is affected by this scattering and absorption in different ways. Bluer (or shorter wavelength) light is easier to scatter. The sky is blue on a cloudless day because the bluer light from the Sun is scattered out of the line of sight. This light “bounces around” off atoms and molecules in our atmosphere and eventually reaches our eye from some random direction – making the sky look blue. Obviously the light from the Sun itself appears slightly reddened by the same effect since the blue light is preferentially removed. At sunset or sunrise, when the Sun is close to the horizon the light from the Sun has to take a longer path through the atmosphere to get to us. More scattering takes place and the Sun appears redder than normal and makes a beautiful sight to see.
In spiral galaxies, the length of the path the light takes through the galaxy before it gets out and heads towards us depends on our viewing angle. When we see a spiral galaxy face-on the light has the shortest possible path out of the galaxy. By contrast, in an edge-on galaxy, the light must travel through most of the disk before getting out. We expect then that if scattering is important, edge-on galaxies will appear to be redder than face-on galaxies – for similar reasons that sunsets are red. The big question here though is “is scattering important”. Put another way we want to ask “are the disks of spiral galaxies transparent?”. We enjoy a fairly clear view of the extragalactic sky out of our spiral galaxy (the Milky Way), which suggested to early researchers than spiral galaxies probably were transparent. However it is also clear that there is a lot of “extinction due to dust” (our Astronomers terminology for the effect of scattering and absorption of light by particles in the inter-stellar medium) when we look towards the Galactic centre.
So what’s the problem of just looking at a bunch of spiral galaxies and seeing if they get redder as they get edge-on? Well nothing… except that you need to know you’re definitely looking at spirals, and you need to figure out how to measure how edge-on the spirals are. This of course is where Galaxy Zoo helps out so much. Thanks to you we now have an enormous number of visually classified unquestionably spiral galaxies. You even picked out the edge-on ones for us. We can also use the “axial ratios” (the ratio of the maximum dimension to the minimum dimension) of the galaxies from Sloan, which (with some assumptions about how thin the average galaxy is when it’s totally edge-on) gives an estimate of the exact angle of the galaxy’s orientation to us.
And what we’re finding is that spirals definitely get redder as they get more edge-on. So extinction due to dust is clearly important. Because Sloan measures the galaxies in 5 different wavelengths, we can make 4 Sloan colours (in Astronomy the colour is just the difference in the brightness in two different bands) and look at the relative amount of extinction with wavelength which provides information on the source of the scattering and absorption. We can also go to other surveys (for example UKIDSS which measures near-infra red light) to extend this further for some of the galaxies.
Extinction seems to be quite a hot topic lately with Sloan data, but what we have which other researchers don’t is the Galaxy Zoo classifications. They have to use other estimates of if the galaxy is a spiral or not, such as how concentrated the light is, or the exact details of the light profile. Neither is as simple or as reliable as having a human just look at the galaxy. Measuring the amount of extinction is important because it’s been largely neglected in studies using Sloan data up until now. The physical parameters of a galaxy ought not to depend on our viewing angle, but when researchers use colours and luminosities to estimate the star formation history or stellar mass of a spiral galaxy the answer will depend on viewing angle if extinction due to dust is not corrected for. More importantly, elliptical galaxies do not suffer from this effect, so if you compare the mean properties of ellipticals and spirals your answer will be biased by the effect of dust.
So most red spirals seem to be edge-on dusty star forming galaxies which would be normal blue spirals if seen face-on…. but this can’t explain all red spirals. We can still see a significant population of red face-on spirals, and by measuring the average amount of reddening we will even be able to pick out the edge-on spirals which would still be red if seen face-on.
I moved to Portsmouth in October and I was delighted to start working with the Galaxy Zoo team and data. I knew about the project (and even classified a handful of galaxies) before I moved here. I’m currently working on a short paper describing what I’ve told you about here and hope to have it submitted early in the New Year.
Merry Christmas!
Some example images:
A blue face-on spiral galaxy.
A red face-on spiral galaxy.
A red edge-on spiral galaxy.
Mergers Paper submitted
This is from Dan Darg, a graduate student at Oxford, who’s been working on the mergers:
The mergers paper is finally out and will be quite a tour de force. We are confident Galaxy Zoo is the largest visually examined parent sample from which any merger sample has ever been derived and we were able to put together ~3000 merging systems. By contrast, a decade or so ago, a sample with 20 mergers would have been considered a `large’ sample. Galaxy Zoo has thus enabled us to examine several of the key properties of merging galaxies. These include their colours, (stellar) masses, environment, star-formation rates and AGN activity.
The paper is quite long but should be fairly readable to a general audience. I begin in section 1 by an overview of the issues that concern mergers in modern astrophysics and previous methods to find them. This gives us a means to contrast and compare the Galaxy Zoo method which we believe has several advantages.
In section 2 I describe the construction of our catalogue of ~3000 mergers. Here you can see exactly how your votes were used to find the most robust merging systems and is well worth a read (especially if you want to see what issues arose and what we’ll try to overcome in the Galaxy Zoo 2 project).
In section 3 we start to look at results, starting with colour-magnitude digrams since these are the most direct things we detect when we look at pretty much anything in astronomy, i.e. how much and what colour light is coming from mergers. We compared the light with that from a randomly select “control” sample of galaxies taken from SDSS and found that our mergers have a wider spread in colour! In particular, we found a lot of very “blue” looking galaxies in mergers. This can be interpreted to mean that mergers involve (or bring about) new star formation.
We then found some useful results in section 4. Firstly, we estimated the fraction of galaxies in the local universe involved in a major merger. This sort of thing has been sought a lot in modern research and our figure, 1-3%, is very much in the range of expectation. We also were able to estimate something new though, namely, the fraction of spiral to elliptical galaxies in mergers. No other empirical study to date has been able to do this. Interestingly, we found more spirals in mergers than ellipticals compared with the global population!
In section 5 and 6 we studied the environments and stellar masses of our merging galaxies and found that our merging galaxies tended to occupy slightly denser environments and, ellipticals in particular in mergers, seemed to be more massive than their control counterparts.
In section 7 we studied the spectra of our mergers in order to figure which ones had Active Galactic Nuclei, which ones are producing lots of new stars and which ones are inactive. All of these processes and properties are important to our understanding of how galaxies form and evolve and our paper will hopefully provide the impetus for lots of new projects that seek to answer these questions.
Many thanks to all you all for pressing that “merger” button! Lots of interesting science is coming out of it!
Dan
Galaxy Zoo 