Chris Lintott’s Universe

I think I made the lot of the sub-mm astronomer, working extremely hard just to identify blobs, sound pretty thankless earlier today. Strangely, I managed to do so without even complaining that the worst thing about using these short-wavelength radio waves is that most of them are absorbed by the Earth’s atmosphere so unless you’re high up, you might as well not bother.

One solution is to go as high as you can; I’m in favour of this because it means I get to go to Hawaii or Spain, but an international collaboration of astronomers has a much better idea.

BLAST hangs from balloon.

The BLAST collaboration have been flying their satellite underneath a balloon, getting high above most of that pesky atmospheric water. I’ve just come from a talk which detailed their results on a set of galaxies, but Wednesday night offers a chance for you to ride along with the BLAST team. BBC4′s Storyville thread will be featuring an excellent documentary about the project at 10pm GMT.

I was lucky enough to see a preview disk, and it’s brilliant, one of the best scientific documentaries I’ve seen for a long while. Watch it (there’s a list of opportunities here for those of you not in the UK) and feel even more amazed at the lengths sub-mm astronomers are driven to.

Update : Watch the trailer!

Hat tip : Andrew Jaffe for reminding me to post about Blast! the movie.

It’s difficult, as someone who uses telescopes which work in the sub-mm – effectively short-wave radio – it’s difficult not to be jealous of optical astronomers, many of whom are busy in the exhibit hall giving out beautiful posters of their latest hits. Instead, we end up often with spectra, or at best with a picture like this, obtained by the state of the art SCUBA camera on the JCMT.

View from the JCMT's SCUBA camera

I remember SCUBA-guru Rob Ivison’s description of the field on the Sky at Night as ‘blobology’ which hits the nail on the head. When these blobs were first discovered a decade or so ago, no-one knew what they were.

Worse, this simple question turns out to be harder to answer than you might think because the resolution in the sub-mm is so poor. When we look at a sub-mm image, we’re looking at a blurred view of the Universe. If you pointed a big optical telescope at the blob in the image above, the odds are that you’d see many separate galaxies within the one blob. Which of them is responsible for the blob? We wouldn’t know. Rather than jump straight to the optical, therefore, astronomers look deep in longer wavelength radio. Anything we see in the radio is then assumed to correspond to the sub-mm blob, and we’ll have a precise enough position to go chasing the thing with optical telescopes, allowing us to measure the distance.

This technique works for about half the sources, and the orthodox conclusion is that these are rapidly star-forming massive galaxies, the likely precursors of today’s old red and dead ellipticals. What about the other half? My assumption had always been that these were much like the others, but were radio quiet or otherwise difficult to pin down.

In a talk by Kartik Sheth of Caltech here at the American Astronomical Society meeting this morning, I realised I might have to rethink. Sheth’s group used the CARMA array to look directly at one sub-mm galaxy which hadn’t been matched with a counterpart.

The CARMA mm array.

They were able to sidestep the need for radio, and go directly to Hubble data which covered the field.

The Antennae Galaxies

To their surprise, the system was much nearer than other sub-mm galaxies. The best analogue seems to be a merging system, rather like the well-known Antennae which are pictured above. Is this a one-off? Are other nearby galaxies lurking among the distant blobs SCUBA sees? We’ll need, it seems much more data before we can say for sure.

I’m on top of a mountain in Spain; if you’d like to join me on my observing run then I’ll be posting updates on the Galaxy Zoo Blog.

Imagine being in our solar system, standing just where the Earth is now, roughly four and a half billion years ago. Around you would be the detritus of star formation, left over material forming a protoplanetary disk from which the planets are coalescing. Understanding just how this disk of dust and gas became the eight planets of the Solar System is one of the fundamental questions of astronomy, and in the penultimate plenary talk today David Wilner from the Harvard-Smithsonian Centre for Astronomy took us through the latest results from this fast moving field.

There are just two major problems with looking for these disks. The first is that most of the disk is cold, dark and not shining, and the second is that they are very small and thus difficult to image. For a nearby example, you’d be lucky if your disk appeared to have a size of a 1/4000th of a degree.

Battling manfully against these challenges, astronomers have had extraordinary success to understand these systems. To get around the first, we can look for comparatively rare chemicals such as hydrogen cyanide (HCN) or Carbon Monoxide (CO) and use these to trace the structure of the disk.

Through these and other methods, we can now measure the mass of a typical disk, and find that 1/100th of the mass of the Sun is typical; that’s a good number because you have enough stuff to form a Jupiter and a few other planets besides, but it does illustrate how small a proportion of the whole we’re talking about. We can also work out a lifetime for the disk. About half of the material disappears in the first 3 million years, and most of the rest in another 2 million; the blink of an eye in astronomical terms.

The next stage is to try and see these things; to do that, we string together light from many separate telescopes, producing images which are as good as telescopes many times larger than we could possibly produce. Unfortunately, perhaps, the disks tend to look just like blobs, but at least we are seeing the places where planets are forming for the first time.

So how do these disks form stars? Well, we have to first get dust grains to stick together. As the clumps get larger, then their gravity can attract further material to keep them growing all the time. If there’s enough material, then gas will be attracted too and you can form a nice new Jupiter. Remarkably, we can actually see evidence for each of these processes in the details of our observations of protoplanetary disks.

One nightmare researchers like the speaker have is their inability to prove that the disks they’re seeing are the same as those which go on to produce planets. The best evidence that they’re getting it right is the presence of large gaps in some of the studied disks; just as small moons of Saturn can create gaps in the rings, so small, newly formed planets still embedded in a protoplanetary disk might produce the gaps we see.

In some cases it’s even possible to make this connection directly. TW Hyd is a star which is known to have a disk, with an observed hole. Earlier this year, a large planet (about 10 times Jupiter’s mass) was detected orbiting the star, and while this planet isn’t the one creating the observed hole at least there’s a system with both a disrupted disk and a planet.

Our early Solar System, then, will have gaps in the disk where Earth and the rest are forming. For now, we can only see such things in detail in our mind’s eye, or in the distorted world of computer simulations. That might chance soon though, with the advent of the ALMA array high up in the Chilean Atacama desert. ALMA’s high resolution images might reveal not only the gaps in the disks, but also material streaming into those gaps to form smaller dust disks around the nascent planets. In viewing these secondary disks, we will be seeing not the birth of planets, but the birth of systems of moons like those around Jupiter. Now that’s a view worth waiting four and half billion years to get.

The Great Observatories Origins Deep Survey (GOODS) : An Observational Legacy for Studying Galaxy Evolution
Prof Marc Dickinson

The following was written during the final plenary talk of the first day at the American Astronomical Society Meeting in St Louis. I was going to post as we went along, but the wireless connection in the meeting room was very flaky (probably just as well – it means the audience are paying attention to the speaker!) I’m posting it in a lump near the end of the talk. Images to follow.

In the introduction to this talk, we were told that the hallmark of modern astronomical research is the survey, and it’s certainly true that astronomers have learnt to make use of projects which carefully chart sections of the sky. The speaker began by reminding us that it’s more than a decade since the Hubble Deep Field – as he said, every time you get a new telescope the temptation is to push it to its limits. After 150 orbits staring at the same field, it turned out Hubble was excellent at seeing the distant Universe.

The data were released, and then most other major observatories all observed the same field, producing hundreds of papers to understand this region of the sky. Not bad for a patch just 2.5 arcminutes square (an arcminute is a sixtieth of a degree). But the question is, with such a small area how can we be sure that we have a fair census? What if that patch turned out to be unusual in some way? Even if we’ve got lucky and picked the right region, then rare objects will be missed entirely.

GOODS is the solution to this problem; using Chandra in the x-ray, Spitzer in the infrared and Hubble’s ACS camera (not available at the time of the original HDF), they set out to cover two regions, each thirty times larger than the original Hubble Deep Field. The aim was to disentangle the evolution of normal galaxies in the first third of the Universe’s evolution, taking a census of black hole growth and activity, understanding how and when star formation takes place and so on.

Each telescope had a different role to play; Spitzer, for example, in the mid Infrared allowed the team to weight the galaxies. The total stellar mass in a galaxy turns out to be very sensitive to the brightness in this band (although you have to worry about the evolution of the stars, we’ve got pretty good at doing that). As before, other observatories have chipped in, with GALEX providing the Ultraviolet, for example, and the SCUBA camera on the JCMT providing a view of the cold early Universe in the sub-mm region of the spectrum.

Astronomers are greedy, though, and as well as imaging we demand data. The first step in understanding an object is to work out how far away it is, and for objects as far as those in GOODS that means measuring their redshift. Lines in their spectrum will be shifted due to the expansion of the Universe; in all more than 5000 GOODS objects have had their distance measured. That’s not a huge number compared to something like the Sloan Digital Sky Survey, but the objects are much further away (so more telescope time is required per object to get a decent spectrum).

The results were far too numerous to go into here, but there are some nice highlights. For example, we can show that galaxies were, on average, smaller in the past, just as you’d expect if the systems we see around us today were assembled by mergers of smaller galaxies. Arguments are raging about the star formation history of the Universe; we know our Universe is past its peak, forming ten times as many stars about 6 billion years ago as it does today, but the GOODS data suggest that looking further back the rate drops once more.

One of the reasons this is controversial is that most of the energy emitted by the newly formed stars is absorbed and then reradiated by dust. This process makes the galaxies bright in the infrared, and so Spitzer can help here. Prof Dickinson went so far as to call the early Universe (before z=0.7 if you understand and care about redshifts) ‘the age of obscurity’.

As well as changing sizes and star formation rates, the population of galaxies has changed too. In the first third of the Universe’s evolution, the average massive galaxy was what is called a ULIRG – an Ultra-Luminous InfraRed Galaxy. Spin forward to today and you’ll find that in the present day the typical massive galaxy is an elliptical – old, red and dead, devoid of star formation and about as far from a ULIRG as it’s possible to be while still being a massive galaxy.

Disentangling everything that might contribute to the light we receive from a galaxy is hard work, to say the least. The team looked at a set of galaxies which had an excess of light in the mid-infrared – the massive galaxies described in the previous paragraph. It’s tempting to assume that the infrared is due entirely to star formation, but by looking with Chandra they detected x-rays from hidden Active Galactic Nuclei. In other words, these galaxies are not just forming stars, but half of all galaxies had black holes at their centre which were in the act of consuming large amounts of material. As Prof Dickinson said, it seems that around 4 billion years after the Big Bang was an important time in a galaxy’s life.

Perhaps one of the most surprising results is the presence of another population of galaxies at this time. There seem to be a set of galaxies which aren’t doing very much at all – they’ve already formed their stars and are already quietly and passively enjoying the galactic equivalent of late middle age. One mystery is that there are smaller for their weights than we’d expect – and it’s hard to imagine how they might ‘puff up’ to see the galaxies that we see today.

Looking further back, the team managed to detected light emitted from galaxies when the Universe was not much more than a billion years old. Even at this time, there’s evidence for a fairly mature stellar population, so substantial numbers of stars must have been formed before the epoch of the earliest galaxies astronomers have seen to date. They have some candidates from this early epoch, but it’ll have to wait for the next generation space telescopes to confirm these detections, so don’t hold your breath.

As if all of that wasn’t enough, the team realised that by going back to the same parts of the sky every 40 or so days, they stood a great chance of discovering distant supernovae. Of those they discovered, almost 50 are a particular type of exploding star – supernovae type 1a. These explosions seem to contain a clue to their true luminosity, and so by comparing how bright they appear with how bright they actually are we can try and measure the acceleration of the Universe.

At this stage I’m being to feel a bit breathless after all the work the GOODS team have done. Prof Dickinson is finishing his talk by asking ‘are we done yet’? The answer, perhaps not surprisingly, is an emphatic no. One of the major problems is tht the measured star formation rate should tie up with the measurements of the total number and mass of stars –and they don’t. They also know there must be more black holes hiding, because they see energetic x-rays with no obvious source. Black holes hiding behind dust are the obvious candidates.

What we really need is a new telescope, working in the far infrared. ESA’s Herschel space telescope – larger than any other telescope ever to fly into space – is due for launch early next year is designed to solve this problem, and will take a long early look at the GOODS fields. I’m planning to head straight from AAS to go and visit Herschel which is undergoing final tests, so it’s great to hear that people are already anticipating the data it will provide.

As you probably realised, my trip to Hawaii was more or less a complete washout. Of the four nights we had on the telescope, we made it to the summit for one and a half of them. The last night was the most depressing, when we sat there for hours waiting for fog to clear only for it to start snowing heavily. Once that happens, you need a team with shovels to be able to open up and it’s time to head down. We did manage to get about an hour’s data on the third night, for a program which didn’t need as good conditions as mine did, providing data on targets which will be viewed by the new Herschel telescope.

Herschel doesn’t need to worry about snowstorms, as it’s ESA’s new space telescope. With a 3.5m mirror, it will be the largest telescope ever to fly. Designed to work in the far-IR – a region of the spectrum that hasn’t been covered by recent missions – it should produce spectacular views of the coolest bits of the Universe, from nearby star formation to the most distant galaxies. In order to make sense of the results expected when it launches later this year, scientists are currently carrying out large surveys with existing ground based telescopes. These will be used to calibrate and to help interpret Herschel’s results – which will no doubt send scientists scurrying back to Mauna Kea. If it isn’t snowing, that is.

No telescopes open and more snow on the way. We could do some laundry for excitement, but are saving that for tomorrow in case we need more excitement then. Chris needs cheering up – please help!

And in a rash moment, he gave posting access to his fellow observers, heheh… so
Chris Quote of the day: (we were walking past the visitor centre where someone was grappling with a shiny metal thermos) “Look, that man has a telescope!” Um… yeah, that’s why they pay you the big bucks, Chris…
Survival Tactic of the day: not eating the Prawns of Death, which re-appeared again on the salad buffet. They’re kinda brown now.

The above image is from the latest release from the context camera on Mars Reconnaissance Orbiter which, Emily reports, has now covered 20% of Mars at a resolution of 6m per pixel. Ironic that this should come out just after I’d written about faces on Mars for the BBC, but it does fit with my being told to be more cheerful about the observing run. So, reasons to be cheerful :

1. I’ve made it up the mountain; not to the summit just yet, but close enough to get there if a miracle happens and we get a clear night tonight (it’s currently 6.15am on Wednesday, local time).

2. I have no excuse for getting a large percentage of the things on my ‘to-do’ list done. Have internet connection, will travel.

3. The new instruments on both JCMT and UKIRT are performing brilliantly. HARP – essentially a 3d camera for the sub-mm – is a joy to use, and I’ve already written this year about the survey that UKIRT’s new camera has produced.

4. Cloudy observing runs mean an excuse to come back.

5. The residence up here, Hale Pohaku, has ice cream available 24 hours a day. With proper cones and everything.

At about five am this morning, two thirds of the way through my second shift on the telescope, I went outside to watch the dawn. The peak immediately behind the JCMT is called Pu’u Poliahu and I decided that would be the perfect spot to watch the Sun come up. Poliahu is the Hawai’ian snow goddess, who was constantly at war with her sister, the volcano god Pele. Pele’s home is the still active Mauna Loa, whereas Poliahu lived on the summit of Mauna Kea which is frequently snow covered. Pu’u Poliahu is therefore a sacred site, but as the place where the first astronomical site testing on the mountain was done, I suppose it might be considered sacred to astronomers too!

The sky was already bright when I stepped out of the door, with a crescent moon hanging about the summit ridge which is home to Gemini, UKIRT and several other telescopes. I walked through one of the JCMT’s neighbours down here in ‘sub-mm valley’, the SMA which consists of eight small dishes, and began climbing the mountain. I could see Jupiter extremely low on the horizon, and off to the right I could see the neighbouring island of Maui sticking above the clouds.

As I climbed higher, I began to feel the effects of the altitude. Climbing even a small hill at more than 14,000 feet above sea level is not easy, and I found myself becoming short of breath. I was also being blown about a bit by an extremely strong wind cutting across the summit, gusts of which blew me from one side of the track to the other. I had my back to the West, and between concentrating on breathing and resisting the wind I didn’t turn round to look at the dawn until I reached the top.

My pictures – taken while crouching down trying to shelter the camera from the wind – don’t do the sight justice. With the crescent moon above the greatest collection of professional telescopes anywhere in the world, the colour of the dawn was a deep red, purple low on the horizon rising to a golden yellow higher up. There were still stars visible in the sky as well as the Moon, and most of the telescopes were still open, most of them pointing toward me, away from the rising Sun.

I know it may be hard to believe, but sitting up there I was thinking of all the times when doing research feels like a hard slog, a prison sentence in front of a computer which won’t cooperate. Combined with the excellent data we got last night, it’s trips like this that remind me why I’m doing any of this in the first place. All I could think about (apart from the need to avoid being literally blown away) was how incredibly, incredibly lucky I am. I think I stayed up there for about twenty minutes, not able to tear my eyes away from the colours laid out in front of me (and realising that clouds are useful for something!).

And walking back down, frozen but ecstatic, I thought about how unique this wonderful island is. On the way up to the telescope, we’d looked over and seen the glow of the vents from one of the world’s most active volcanoes. Where else in the world could you find such an amazing variety within an area not much bigger than greater London? I also think I found the perfect spot to capture almost all of Mauna Kea’s telescopes on pixels.

From left to right: Subaru, Keck, IRTF (NASA), Canada-France-Hawaii Telescope, Gemini North, Uni. Hawaii, UKIRT, small Uni. Hawaii dome and in valley JCMT and CSO.

I love my job.

It’s 7.20am. I started my shift when we left the astronomer’s residence at 8pm. It’ll be at least another three, probably more like four hours until I’m back in bed. And then we’ll do it all again tomorrow.

And yet getting fantastic data with Harp, the new instrument on the JCMT, can make react like this (spontaneous movement captured by the webcam). It’s not even my data as the weather’s still preventing us from doing what we came here for.

I went out and watched the dawn earlier, but I’ll save that story for when I’ve got the pictures off the digital camera.