Archive for the ‘ground based observing’ Category

Dusty Galaxies & Gravitational Telescopes

November 9, 2010

It was an exciting time at the end of last week when the H-ATLAS consortium’s first paper to the journal Science came out. As a co-author I’ve been aware of this result for some time, but it was interesting to see how it got taken up by the press etc..

What we’ve found is that some bright sources seen by Herschel that appear to be associated with fairly nearby galaxies, in cosmological terms at least, are in fact dusty objects behind those nearby galaxies, having their far-IR light amplified through gravitational lensing. The process is illustrated in this figure form one of our press releases.

Herschel finds gravitationally lensed dusty galaxies

Herschel finds gravitationally lensed dusty galaxies

This result started off a long time ago, when the author of the paper, Dr Mattia Negrello, produced models in his PhD thesis of the sources we might expect to find in the Herschel surveys and came to the conclusion that many of the brightest objects would be the result of gravitational lensing. This result was included in the proposal for the H-ATLAS large area survey but I suspect that a fair number of us thought that this aspect of the proposal was a long shot – hugely important if it worked, but not that likely to be the case.

When the first H-ATLAS data came in and we started looking at the brightest reddest sources, though, it looked as if Mattia might have been onto something after all. But we couldn’t be sure. What followed was a rapid dash around many telescopes to get the multiwavelength data needed to confirm the nature of these objects. We needed optical and near-IR imaging, some of which came from Keck, we needed high resolution submm interferometry, which came form the SMA, and we needed submm spectroscopy, which came from the CSO and PdB interferometers. More data is coming from Spitzer and elsewhere, and this will appear in future papers. This is truly multiwavelength astronomy at its best, bringing a wide variety of tools and techniques together to produce the final answer.

And that answer is that Mattia was right, and there are lots of lenses to be found in the Herschel surveys. More than that, the lenses are easy to find. Previous searches for lenses in the optical and radio have had hit rates – ie. the number of lenses found to number of candidates looked at – as low as 1 in 1000. With Herschel, we seem to have a hit rate of 100%.

This has several implications. Firstly we can use the lenses as gravitational telescopes, allowing us to look at very distant objects that are much fainter than would otherwise be possible. Secondly, since mass is responsible for the lensing effect, we can use these systems to look at dark matter and how it evolves.

It’s early days yet, and the initial crop of lenses from H-ATLAS are just 5 in number, but this was based on less than 3% of the final H-ATLAS survey, and there are other Herschel surveys, like HerMES, that are adding to the database. Larger surveys with these lenses central to the science case are also planned, though we have yet to be awarded the time.

This result is also a great example of how science works. Mattia came up with this prediction as a student and has tested it in his postdoctoral work. It’s not often that the predictions and tests are done by the same person, but this is generally how things are meant to go.

The media, needless to say, has been quite interested. The story has been picked up from India to Italy. It’s also appeared on David Ike’s forums though quite where this result fits in with UFOs and alien conspiracy theories I don’t know. Perhaps most significant is that the BBC Today programme’s science correspondent was moved to write about it on his blog even though BBC journalists were on strike that day.

All in all, a great achievement for Mattia, for H-ATLAS and for Herschel!


The ground campaign

July 29, 2010

While Herschel is a wonderful instrument and delivering great results, we can’t achieve our science goals without other observations. I’m currently at Mauna Kea working on followup observations with the Sub-Millimetre Array of sources detected by Herschel. This observing run is just a small part of the large campaign of ground-based observations needed by the large Herschel surveys to find out what’s really going on in the sources we’ve detected.

For the large galaxy surveys I’m involved with among the many things we need to do are to pin down the positions of the sources seen by Herschel, so that we can find counterparts at other wavelengths, obtain spectroscopy in the optical or other bands to measure the redshifts of the sources and to determine the relative importance of star formation or black hole accretion in powering them, get higher resolution images of the sources in the submillimetre so that we can better understand the relationship between dust emission and what’s seen at other wavelengths, and get better, deeper images in the optical and near infrared so that we can see how the stars are distributed in these objects.

The observations from the SMA are steps forward on submm imaging and obtaining better positions.

Some of the antennae of the Submillimetre Array

One of the nice things about observing at the SMA is that the control room has an oxygen enriched atmosphere, so that most of the effects of altitude can be avoided. You can read more about the overall experience of an observing trip to Mauna Kea here in an article I wrote a while back for Clarkesworld magazine.

Doomsday Approaches

December 14, 2009

The funding axe is about to arrive in the UK. STFC council will meet tomorrow to approve the plans, with the details coming out on Wednesday afternoon.

Further discussion available here, here, and here.

There’ll also be a major Herschel press briefing on Wednesday afternoon. We’ll try to cover that here, but I hope you’ll understand if we’re a bit distracted by news about the cuts.

News and more news…

December 11, 2009

Next week will see the first science releases from Herschel at a big ESA press and science event in Madrid. There will be lots of exciting new science results and some stunning new images to look at. We’ll do our best to cover things here, but also look at all the other usual sources of information like ESA, the BBC and Cardiff’s SPIRE webpages.

Meanwhile, on a more local, UK scale, we’re having a week of ups and downs. Wednesday’s ‘pre-budget report’ announced £600 Million of cuts to ‘higher education, science and research budgets’ which is going to be really painful for the UK academic community. Late yesterday some possibly better news came in with the announcement of the formation of a UK space agency. It’s unclear what form this agency will take, how it will be funded or what it will spend its money on, but it is clear that Space in general is getting a higher profile in government than it has previously had, and its contribution to the UK economy is at last being recognised.

Elsewhere, there are some great new images from UK’s new VISTA telescope, and the launch of the WISE infrared survey satellite is eagerly awaited.

Another UK Astronomy Funding Crisis?

September 30, 2009

Rumours are coming in to the effect that the UK research council that funds astronomy, the STFC, is in the throes of a further funding crisis.

The full and sorry story of the STFCs financial woes, which go back to its formation from the amalgamation of PPARC (who used to fund astrophysics and particle physics in the UK) and the CCLRC (the ‘large labs’ funding council in the UK, looking after Daresbury, Rutherford and Diamond) can be found in great detail here. It had looked as if things were calming down, though we were all rather worried about the current reviews underway on both astronomy facilities and research areas. Worries were heightened today with the following news from STFC:

‘STFC Council policy on grants

STFC Council examined progress of its current science and technology prioritisation exercise at a strategy session on 21 and 22 September. Without prejudging the outcome of the prioritisation, Council agreed that prudent financial management required a re-examination of upcoming grants.

Council therefore agreed that new grants will be issued only to October 2010 in the first instance. This temporary policy is in place pending the outcome of the prioritisation exercise, expected in the New Year.’

From STFC.

This suggests that the current money shortages are so severe that the reviews will lead to substantial changes in priorities, possibly with significant areas of research being cut. Any grants from the current application round, already nearing completion, will not reflect these cuts so, without some way of keeping those grants short term, as was announced today, there is the risk of ‘sending good money after bad’.

One might think that this is a rather paranoid interpretation, but there are other rumours circulating of budget holes at STFC in the tens of millions. Again.

The short term exploitation of Herschel data in the UK is probably safe, but the long term prospects for astronomy don’t look so good this evening…

Meanwhile, there should be another press release from Herschel soon, so I can return you to pretty pictures rather than depressing news.

ALMA Construction Underway

September 26, 2009

Herschel is going to be an amazingly successful mission – what I’ve seen of early data confirms that – but it is not going to be the final word in far-IR and submm astronomy. We’re already planning the next satellite, SPICA, and the next generation ground-based submm camera, SCUBA2, is just being commissioned. The biggest ground-based project in this area, though, is ALMA – the Atacama Large Millimetre Array. This consists of an array of 66 dishes on the high plain of the Andes at Chagnantor, and will give submm astronomers the kind of angular resolution of the Hubble Space Telescope, and sensitivities we can only dream of at the moment.

ALMA is being put together by a combination of European, US and Japanese research organisations. Usually, in such combined projects, the US seems to get all the credit in the media – did you know, for example, that Hubble is a joint NASA-ESA mission? I was thus rather amused to see the latest report on ALMA in Wired to describe it as a European Southern Observatory project. But aside from the sociological aspects the article is interesting and has some great photos of the telescope moving vehicle!

Two up, two down

May 18, 2009

There must be some kind of rule of balance with astronomy projects. No sooner have Herschel and Planck got on their way, but Spitzer runs out of cryogens. This means that two of it’s three instruments are now permanently dead. One of them, IRAC, can carry on, limited to just two of its four channels, but there’s great science to be done with this new mode. I know my colleagues in the SERVS project, one of several large scale legacy programmes for this new ‘warm’ mode, are raring to go.

Meanwhile I’m at the joint Gemini/Subaru conference in Kyoto, Japan. It was just announced here that WFMOS, a giant and highly capable multi-object optical spectrograph planned for Gemini, has been cancelled as it’s just too expensive for the current climate. Only one of the instruments from the much vaunted ‘Aspen Instrumentation Process’ will now be built. This can’t be considered a success for Gemini or for the Aspen process.

The Night Begins

March 30, 2009

My first ever night on Subaru has started. The cirrus hasn’t gone away, but it’s not as bad as it looked when I took the photos yesterday.

We’re currently observing one of the fields to be studied by the Herschel HerMES project. The aim is to get optical data so that we can identify the optical counterparts to the sources that Herschel will find in HerMES.

Let’s hope the weather holds up!


March 29, 2009

While Herschel will be a great far-IR observatory, for a lot of our science goals we need data at other wavelengths as well. One of the projects I’m working on with Herschel is the HerMES deep cosmological survey. We aim to uncover the history of dusty galaxies and their role in the universe by getting very deep observations with Herschel. However, to fully understand the objects that Herschel finds we need to match the Herschel objects up with sources at other wavelengths.

I’m currently in Hawaii at the Mauna Kea Observatory to start to get the deep optical data we need for this task. I’ll be observing on the Subaru telescope, of which more later. Tonight is my acclimatization night, staying 24 hours at 10000 feet altitude so that I’m functional when I get to the telescope at 14000 feet tomorrow night.

Unfortunately the weather isn’t looking great…

Rather too much cirrus cloud for good observing

Rather too much cirrus cloud for good observing

The weather forecast for the next few days is that the sky should stay like this, which wouldn’t be good.

Fingers crossed that it improves!

Of course one thing Herschel won’t suffer from is weather in space.