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Hubble Flash

Posted in The Universe and Stuff with tags , , , , , on September 9, 2009 by telescoper

Just a quick post to point out that brand new “Early Release” images have just appeared following the recent refurbishment of the Hubble Space Telescope.

You can read the accompanying press release here, so I’ll just post this brief description:

These four images are among the first observations made by the new Wide Field Camera 3 aboard the upgraded NASA Hubble Space Telescope.

The image at top left shows NGC 6302, a butterfly-shaped nebula surrounding a dying star. At top right is a picture of a clash among members of a galactic grouping called Stephan’s Quintet. The image at bottom left gives viewers a panoramic portrait of a colorful assortment of 100,000 stars residing in the crowded core of Omega Centauri, a giant globular cluster. At bottom right, an eerie pillar of star birth in the Carina Nebula rises from a sea of greenish-colored clouds.

My own favourite has to be Stephan’s Quintet, but they all look pretty fantastic.

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Cosmic Haiku

Posted in Poetry, The Universe and Stuff with tags , , , on September 6, 2009 by telescoper

I haven’t had much time to post today and will probably be too busy next week for anything too substantial, so I thought I’d resort to a bit of audience participation. How about a few Haiku on themes connected to astronomy, cosmology or physics?

Don’t be worried about making the style of your contributions too authentic, just make sure they are 17 syllables in total, and split into three lines of 5, 7 and 5 syllables respectively.

Here’s a few of my own to give you an idea!

Quantum Gravity:
The troublesome double-act
Of Little and Large

Gravity’s waves are
Traceless; which does not mean they
Can never be found

The Big Bang wasn’t
So big, at least not when you
Think in decibels.

Cosmological
Constant and Dark Energy
Are vacuous names

Microwave Background
Photons remember a time
When they were hotter

Isotropic and
Homogeneous metric?
Robertson-Walker

Galaxies evolve
In a complicated way
We don’t understand

Acceleration:
Type Ia Supernovae
Gave us the first clue

Cosmic Inflation
Could have stretched the Universe
And made it flatter

Astrophysicist
Is what I’m told is my Job
Title. Whatever.

Contributions welcome via the comments box. The best one gets a chance to win Bully’s star prize.

12 Comments »

The Inductive Detective

Posted in Bad Statistics, Literature, The Universe and Stuff with tags , , , , , , , on September 4, 2009 by telescoper

I was watching an old episode of Sherlock Holmes last night – from the classic  Granada TV series featuring Jeremy Brett’s brilliant (and splendidly camp) portrayal of the eponymous detective. One of the  things that fascinates me about these and other detective stories is how often they use the word “deduction” to describe the logical methods involved in solving a crime.

As a matter of fact, what Holmes generally uses is not really deduction at all, but inference (a process which is predominantly inductive).

In deductive reasoning, one tries to tease out the logical consequences of a premise; the resulting conclusions are, generally speaking, more specific than the premise. “If these are the general rules, what are the consequences for this particular situation?” is the kind of question one can answer using deduction.

The kind of reasoning of reasoning Holmes employs, however, is essentially opposite to this. The  question being answered is of the form: “From a particular set of observations, what can we infer about the more general circumstances that relating to them?”. The following example from a Study in Scarlet is exactly of this type:

From a drop of water a logician could infer the possibility of an Atlantic or a Niagara without having seen or heard of one or the other.

The word “possibility” makes it clear that no certainty is attached to the actual existence of either the Atlantic or Niagara, but the implication is that observations of (and perhaps experiments on) a single water drop could allow one to infer sufficient of the general properties of water in order to use them to deduce the possible existence of other phenomena. The fundamental process is inductive rather than deductive, although deductions do play a role once general rules have been established.

In the example quoted there is  an inductive step between the water drop and the general physical and chemical properties of water and then a deductive step that shows that these laws could describe the Atlantic Ocean. Deduction involves going from theoretical axioms to observations whereas induction  is the reverse process.

I’m probably labouring this distinction, but the main point of doing so is that a great deal of science is fundamentally inferential and, as a consequence, it entails dealing with inferences (or guesses or conjectures) that are inherently uncertain as to their application to real facts. Dealing with these uncertain aspects requires a more general kind of logic than the  simple Boolean form employed in deductive reasoning. This side of the scientific method is sadly neglected in most approaches to science education.

In physics, the attitude is usually to establish the rules (“the laws of physics”) as axioms (though perhaps giving some experimental justification). Students are then taught to solve problems which generally involve working out particular consequences of these laws. This is all deductive. I’ve got nothing against this as it is what a great deal of theoretical research in physics is actually like, it forms an essential part of the training of an physicist.

However, one of the aims of physics – especially fundamental physics – is to try to establish what the laws of nature actually are from observations of particular outcomes. It would be simplistic to say that this was entirely inductive in character. Sometimes deduction plays an important role in scientific discoveries. For example,  Albert Einstein deduced his Special Theory of Relativity from a postulate that the speed of light was constant for all observers in uniform relative motion. However, the motivation for this entire chain of reasoning arose from previous studies of eletromagnetism which involved a complicated interplay between experiment and theory that eventually led to Maxwell’s equations. Deduction and induction are both involved at some level in a kind of dialectical relationship.

The synthesis of the two approaches requires an evaluation of the evidence the data provides concerning the different theories. This evidence is rarely conclusive, so  a wider range of logical possibilities than “true” or “false” needs to be accommodated. Fortunately, there is a quantitative and logically rigorous way of doing this. It is called Bayesian probability. In this way of reasoning,  the probability (a number between 0 and 1 attached to a hypothesis, model, or anything that can be described as a logical proposition of some sort) represents the extent to which a given set of data supports the given hypothesis.  The calculus of probabilities only reduces to Boolean algebra when the probabilities of all hypothesese involved are either unity (certainly true) or zero (certainly false). In between “true” and “false” there are varying degrees of “uncertain” represented by a number between 0 and 1, i.e. the probability.

Overlooking the importance of inductive reasoning has led to numerous pathological developments that have hindered the growth of science. One example is the widespread and remarkably naive devotion that many scientists have towards the philosophy of the anti-inductivist Karl Popper; his doctrine of falsifiability has led to an unhealthy neglect of  an essential fact of probabilistic reasoning, namely that data can make theories more probable. More generally, the rise of the empiricist philosophical tradition that stems from David Hume (another anti-inductivist) spawned the frequentist conception of probability, with its regrettable legacy of confusion and irrationality.

My own field of cosmology provides the largest-scale illustration of this process in action. Theorists make postulates about the contents of the Universe and the laws that describe it and try to calculate what measurable consequences their ideas might have. Observers make measurements as best they can, but these are inevitably restricted in number and accuracy by technical considerations. Over the years, theoretical cosmologists deductively explored the possible ways Einstein’s General Theory of Relativity could be applied to the cosmos at large. Eventually a family of theoretical models was constructed, each of which could, in principle, describe a universe with the same basic properties as ours. But determining which, if any, of these models applied to the real thing required more detailed data.  For example, observations of the properties of individual galaxies led to the inferred presence of cosmologically important quantities of  dark matter. Inference also played a key role in establishing the existence of dark energy as a major part of the overall energy budget of the Universe. The result is now that we have now arrived at a standard model of cosmology which accounts pretty well for most relevant data.

Nothing is certain, of course, and this model may well turn out to be flawed in important ways. All the best detective stories have twists in which the favoured theory turns out to be wrong. But although the puzzle isn’t exactly solved, we’ve got good reasons for thinking we’re nearer to at least some of the answers than we were 20 years ago.

I think Sherlock Holmes would have approved.

15 Comments »

Audio Video Disco

Posted in Biographical, The Universe and Stuff with tags , , on August 26, 2009 by telescoper

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This scary picture is taken from an interactive exhibit in the Weller Galleries of the Royal Observatory at Greenwich, which opened in 2007. The exhibit, I mean, not the Royal Observatory. I remember going down there to record the video segments, but had forgotten all about it until somebody found this image on the net and drew my attention to it.

The exhibit consists of a series of display screens with various astronomical and cosmological concepts and questions on them, along with appropriate images. Visitors touch the screens to bring up the video segments in which distinguished astronomers (or me) attempt to provide explanations.

The lady to the bottom right is probably providing a sign language translation of my contribution. Or she could simply be screaming and waving her hands in terror. Wouldn’t you?

PS. If you want an explanation of the title of this blog post, I’ll translate Audio Video Disco from the latin for you. It means “I hear, I see, I learn”. Since they have to touch the screen, I might have added “I touch” which would be Tango….

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Return of the Clerihews!

Posted in Poetry, The Universe and Stuff with tags , , on August 2, 2009 by telescoper

As a result of an after-dinner discussion at the meeting I attended last week, I’ve decided to put a revised cosmological clerihew collection back online. I’ve removed or edited those that caused the greatest offence, and added a few new ones.

Bernard Carr
Has gone a bit far:
His Anthropic Principle
Makes theories invincible

Sean Carroll
Has me over a barrel
Because the only plausible rhyme
Plugs his new book on Time

The mind of John Barrow
Is not very narrow:
He’s more open than me
To a variable c

Stephen Hawking
Lets a machine do the talking
But even  he can’t vocalize in-
side a black hole horizon.

Joe Silk
Is one of that ilk
Who writes far more articles
Than there are elementary particles

Matt Griffin
Has healthy salad for tiffin
But he’d probably expire
If something went wrong with SPIRE.

Peter Ade
Would never be afraid
To enter his name
In the citation game

Andy Lawrence
Would shed tears in torrents
If they finally got rid
Of the Astrogrid

Steve Maddox
Never eats haddocks
But he’s quite a dab hand
In the optical band

Ofer Lahav
Is awfully suave
But must be getting nervy
About the cancellation of funding for the Dark Energy Survey

Joao Magueijo
Was on the Today Show
Talking some shite
About travelling faster than light

Keith Mason
Said to Lord Drayson
“Can we have some more money?”
He replied “Don’t try to be funny…”

Andrei Linde
Felt rather windy
A peculiar sensation:
The result of internal inflation?

To rhyme Carlos Frenck
I’ve drawn a complete blenk
But I found in the lexicon
A good one for Mexican

When Andrew Jaffe
Plots a new graph he
Thinks fits his theory he’ll
Tell everyone at Imperial

Paul Steinhardt
Said “Lust not after beauty in thine heart”
But why he did so
I really don’t know

Feel free to offer your own through the comments box, after consulting the rules, although I remind you I don’t accept anonymous comments, even if they’re funny.

29 Comments »

Astronomy or Astrophysics?

Posted in The Universe and Stuff with tags , , , , , on July 25, 2009 by telescoper

A chance encounter with the parent of a prospective student the other day led eventually to the question What’s the difference between Astronomy and Astrophysics? This is something I’m asked quite often so I thought I’d comment on here for those who might stumble across it. I teach a first-year course module entitled “Astrophysical Concepts”. One of the things I try to do in the first lecture is explain that difference. The Oxford English Dictionary gives the following primary definition for astronomy:

The science which treats of the constitution, relative positions, and motions of the heavenly bodies; that is, of all the bodies in the material universe outside of the earth, as well as of the earth itself in its relations to them.

Astrophysics, on the other hand, is described as

That branch of astronomy which treats of the physical or chemical properties of the celestial bodies.

So astrophysics is regarded as a subset of astronomy which is primarily concerned with understanding the properties of stars and galaxies, rather than just measuring their positions and motions. It is possible to assign a fairly precise date when astrophysics first came into use in English because, at least in the early years of the subject, it was almost exclusively associated with astronomical spectroscopy. Indeed the OED gives the following text as the first occurence of astrophysics, in 1869:

As a subject for the investigations of the astro-physicist, the examination of the luminous spectras of the heavenly bodies has proved a remarkably fruitful one

The scientific analysis of astronomical spectra began with a paper  William Hyde Wollaston in the Philosophical Transactions of the Royal Society Vol. 102, p. 378, 1802. He was the first person to notice the presence of dark bands in the optical spectrum of the Sun. These bands were subsequently analysed in great detail by Joseph von Fraunhofer in a paper published in 1814 and are now usually known as Fraunhofer lines.  Technical difficulties  made it impossible to obtain spectra of stars other than the Sun for a considerable time, but  William Huggins finally succeeded in 1864. A drawing of his pioneering spectroscope is shown below.

Meanwhile, fundamental work by Gustav Kirchoff and Robert Bunsen had been helping  to establish an understanding the spectra produced by hot gases.  The identification of features in the Sun’s spectrum  with similar lines produced in laboratory experiments led to a breakthrough in our understanding of the Universe whose importance shouldn’t be underestimated. The Sun and stars were inaccessible to direct experimental test during the 19th Century (as they are now). But spectroscopy now made it possible to gather evidence about their chemical composition as well as physical properties. Most importantly, spectroscopy provided definitive evidence that the Sun wasn’t made of some kind of exotic unknowable celestial material, but of the same kind of stuff (mainly Hydrogen) that could be studied on Earth.  This realization opened the possibility of applying the physical understanding gained from small-scale experiments to the largest scale phenomena that could be seen. The science of astrophysics was born. One of the leading journals in which professional astronomers and astrophysicists publish their research is called the Astrophysical Journal, which was founded in 1895 and is still going strong. The central importance of the (still) young field of spectroscopy can be appreciated from the subtitle given to the journal: Initially the branch of physics most important to astrophysics was atomic physics since the lines in optical spectra are produced by electrons jumping between different atomic energy levels. Spectroscopy of course remains a key weapon in the astrophysicist’s arsenal but nowadays the term is taken to mean any application of physical laws to astronomical objects. Over the years, astrophysics has gradually incorporated nuclear and particle physics as well as thermodynamics, relativity and just about every other branch of physics you can think of. I realise, however, that this  isn’t really the answer to the question that potential students want to ask. What they (probably) want to know is what is the difference between undergraduate courses called Astronomy and those called Astrophysics? The answer to this one depends very much on where you want to study. Generally speaking the differences are in fact quite minimal. You probably do a bit more theory in an Astrophysics course than an Astronomy course, for example. Your final-year project might have to be observational or instrumental if you do Astronomy, but might be theoretical in Astrophysics.  If you compare the complete list of modules to be taken, however, the difference will be very small.

Over the last twenty years or so, most Physics departments in the United Kingdom have acquired some form of research group in astronomy or astrophysics and have started to offer undergraduate degrees with some astronomical or astrophysical content. My only advice to prospective students wanting to find which course is for them is to look at the list of modules and projects likely to be offered. You’re unlikely to find the name of the course itself to be very helpful in making a choice. One of the things that drew me into astrophysics as a discipline (my current position is Professor of Theoretical Astrophysics) is that it involves such a wide range of techniques and applications, putting apparently esoteric things together in interesting ways to develop a theoretical understanding of a complicated phenomenon. I only had a very limited opportunity to study astrophysics during my first degree as I specialised in Theoretical Physics.  This wasn’t just a feature of Cambridge. The attitude in most Universities in those days was that you had to learn all the physics before applying it to astronomy. Over the years this has changed, and most departments offer some astronomy right from Year 1. I think this change has been for the better because I think the astronomical setting provides a very exciting context to learn physics. If you want to understand, say, the structure of the Sun you have to include atomic physics, nuclear physics, gravity, thermodynamics, radiative transfer and hydrostatics all at the same time. This sort of thing makes astrophysics a good subject for developing synthetic skills while more traditional physics teaching focusses almost exclusively on analytical skills. Indeed, my first-year Astrophysical Concepts course is really a course about modelling and problem-solving in physics.

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Advanced Fellowships

Posted in Science Politics with tags , , , on July 11, 2009 by telescoper

This is just a quick Newsflash that UK Astronomers will be  interested in (and depressed by). My attention was drawn to it yesterday by Frazer Pearce of Nottingham.

The Science and Technology Facilities Council (STFC) has decided in its finite wisdom to cut in half the number of Advanced Fellowships (AFs) it awards each year, that is from 12 to 6, that number to cover all of Astronomy and Particle Physics.

These fellowships are awarded to researchers who do not have a permanent position but wish to pursue research, and are designed to further the careers of individuals with outstanding potential. They last 5 years – longer than the usual 2-3 year postdoctoral positions and have been for many a scientist an important stepping-stone to an academic career. A very large fraction of my colleagues who have permanent positions were awarded one of these fellowships when they were run by PPARC (including Frazer), as was I myself but, being an Oldie, mine was even pre-PPARC so was in fact given by SERC. Of course the fact that they gave me one doesn’t itself serve as much of a recommendation for continuing them, but it is worth drawing attention to the huge amount of  high quality research done in the UK by holders of these Fellowships.

A number of people have expressed to me their shock at this decision but it doesn’t surprise me at all. For one thing, it’s an open secret that STFC considers the academic community in these areas to be too large so the last thing it wants is more people getting permanent jobs through the AF route.  In any case, STFC’s prime concern is with facilities, not with scientific research.

Who needs half a dozen top class scientists when you can have Moonlite instead?

18 Comments »

Good News, Bad News

Posted in Science Politics with tags , , on May 1, 2009 by telescoper

Further to my gloomy prognosis about the implications of the Budget for astronomy research, I’ve managed to glean the following interpretation of the outcome for the Science & Technology Facilities Council (STFC).

Just to remind you that the situation before the budget settlement was announced last week was truly dire, with  falling exchange rates leading to rises in the cost of subscriptions putting pressure on an already overstretched STFC budget. In fact, STFC actually underspent last year but was not allowed to carry the underspend forward into the tax year beginning this April so that has done nothing to help the imminent financial meltdown. The overall  shortfall for 2009-10 was estimated pre-budget to be about £80 million, meaning that £80 million of current commitments would have to be ditched if nothing was done.

First, the good news. After the budget it has emerged that the Department for Innovation, Universities and Skills (DIUS)  has taken steps to “lend” STFC money to plug the shortfall arising from exchange rate fluctuations. This means the actual shortfall is not going to be as large as the previous estimate.

Now the bad news. There is no new money for STFC,  and there is consequently still a serious gap in the finances. There will have to be about £20 million savings this financial year (against current commitment) and about £30 million next year. Not as bad as £80 million, but still very tough.

At this moment the powers that be are dusting off the Programmatic Review which involved the prioritisation of missions and facilities within the STFC remit. There is also yet another review of ground-based astronomy which is meant to be a long-term thing, but will presumably inform the decision-making process in the short term too.

A line had previously drawn as far down the  list of priorities as funding would permit. Now the available funds are less the line will have to rise and some astronomical projects that thought they were safe will have to be ditched after all. This also depends on whether STFC saves money in other ways,  such as from the grants line or by internal savings within its own administration.

It will be a nervous wait for many of us to see where and the axe will fall next…

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Budget Boost?

Posted in Science Politics with tags , , , , on April 19, 2009 by telescoper

This Wednesday (22nd April 2009) the Chancellor of the Exchequer, Alistair Darling, will deliver the UK government’s budget for this year. The background is of course the economic recession and the consequent collapse of our public finances. The government will have to borrow an estimated £175 billion over the next year, and it likely that taxes will eventually have to rise considerably to balance the books in the longer term.

Rumours are abounding about what will be in the budget and what won’t. According to today’s Observer, the centrepiece is likely to be a £50 billion scheme to revitalize the housing market.  If this is the case then I think it’s a mistake. Our economy has been run for too long on the basis of money raised from inflated property valuations, and we need to take this opportunity to change to a more sustainable way of running the country. Other schemes that may emerge include a £2 billion scheme to help unemployed young people which is a better idea, but much of it would probably be wasted in bureaucracy rather than doing real good.

My own attention will be focussed on whether there is anything in Alistair Darling’s speech that indicates some help for science, particularly fundamental science like physics and astronomy. In yesterday’s Guardian the Astronomer Royal and President of the Royal Society, Lord Martin Rees argued  for an injection of cash to stimulate science and innovation. About a month ago the BBC reported on efforts by Ministers to convince the treasury of the benefit of a £1 billion stimulus package for science along these lines. However, even if the powers that be listen to this argument (which is, in my view, unlikely), any increase in science funding would not necessarily be directed towards fundamental physics. I think if there isn’t anything for those of us working in astronomy in this budget, then we’re completely screwed.

I believe the funding crisis at the Science & Technology Facilities Council (STFC) was precipitated by a conscious government decision to move funds away from blue skies research and into more applied, technology driven areas.  The 2007 Comprehensive Spending Review was extremely tough on STFC but quite generous to some other agencies.  Moreover, within STFC itself there seems to be a shift from science-driven to technology-driven projects,  signalled by the cancellation of projects such as Clover to save a couple of million, and the allocation of funds to projects such as Moonlite which is devoid of any scientific interest and which could end up costing as much as £150 million over the next five years or so.

The true depth of the ongoing STFC crisis is only gradually becoming apparent. It was bad enough to start with, but has been exacerbated by the fall in value of sterling against the euro since 2007 which has meant that the cost of subscriptions to CERN, ESA and ESO have risen dramatically (by about 40%). These form such a large part of STFC’s expenditure – the CERN subscription alone is £70m out of a total budget of around £800m – that it cannot absorb the increased cost and it is now looking to make swingeing cuts on top of the 25% cut in research grants already implemented.

News emerged last week that STFC has abandoned plans to fund any R&D grants for ESA’s Cosmic Vision programme, and there are dark rumours circulating that it is considering cancelling all astronomy grants this year as well as clawing back money already given to universities in previous rounds. I hope these are not true, but I fear the worst.

Cuts on this scale would be devastating, demoralising, and I honestly think would destroy the United Kingdom as a place to do astronomy. They would also signal a complete breakdown of trust between scientists and the research council that is supposed to support them, if that hadn’t happened already.

Incidentally it is noticeable that STFC hasn’t bothered to report any of these matters publically through its website. Instead, the lead story on the STFC news page is about a visit by Prince Andrew to the Rutherford Appleton Lab. No sign yet, then, of the promised improvement in communication between the STFC Executive and its community.

The way I see it, the urgent issue is not whether we get a stimulus package , but whether we even get the bit of sticking plaster that is needed to  saves physics and astronomy from utter ruin. The cost would be a small fraction of the billions lavished on profligate bankers, but I’m not at all sure that the government either appreciates or cares about the scale of the problem.

Anyway, coincidentally, next week sees the Royal Astronomical Society’s National Astronomy Meeting (NAM), which is this year held jointly with the European Astronomical Society’s JENAM at the University of Hertfordshire. I won’t be going because it has unfortunately been organized in term time apparently because European astronomers refuse to attend meetings in the vacations, at least if they’re in places like Hatfield.  STFC representatives  have been invited; it remains to be seen what, if anything, they will have to say.

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Full Blast

Posted in Science Politics, The Universe and Stuff with tags , , , , , on April 9, 2009 by telescoper

Yesterday, Paolo Calisse and I were paid a visit by a reporter (Martin Shipton) and a photographer from Welsh newspaper The Western Mail who wanted to cover the sad story of Clover.

Paolo is heavily involved with Clover, but I was a bit hesitant about doing this because I’m not really part of the Clover team. Paolo suggested it might be an advantage that I wasn’t so directly involved as I might be able to give a more balanced view of the importance of the experiment than him. Anyway, the story came out today in the newspaper and is available online too.

DrThis is the picture they took of me and Paolo in the Clover lab, fiddling with the cryostat. I’ve already had my leg pulled enough about pretending to be an instrumentalist for the photograph so no jokes please…

 

 

 

 

In the same issue of the paper there is another feature about Cardiff’s astronomy research, concerning BLAST (Balloon-borne Large Aperture Submillimetre Telescope). This is a much happier story, as it marks the release of results from a highly successful science run from 2006. In the print version of the Western Mail the two stories were run on the same page, one above the other, making very effectively the point that cutting the funding of the Astronomy Instrumentation Group jeopardizes a great deal of world-leading research besides Clover itself. And when I say “world-leading” I mean it, whatever the RAE panel might have thought.

A deluge of articles about BLAST appeared on the arXiv today, one of which is now published in Nature. I thought I’d put up the abstracts here in order to draw attention to these results. The author lists contain many Cardiff authors and, as you’ll see, the results are both fascinating and wide-ranging. I’ve put links to the arXiv after each abstract:

Title: BLAST: Correlations in the Cosmic Far-Infrared Background at 250, 350, and 500 microns Reveal Clustering of Star-Forming Galaxies

Authors: Marco P. Viero, Peter A. R. Ade, James J. Bock, Edward L. Chapin, Mark J. Devlin, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Carrie J. MacTavish, Gaelen Marsden, Peter G. Martin, Philip Mauskopf, Lorenzo Moncelsi, Mattia Negrello, Calvin B. Netterfield, Luca Olmi, Enzo Pascale, Guillaume Patanchon, Marie Rex, Douglas Scott, Christopher Semisch, Nicholas Thomas, Matthew D. P. Truch, Carole Tucker, Gregory S. Tucker, Donald V. Wiebe

We detect correlations in the cosmic far-infrared background due to the clustering of star-forming galaxies, in observations made with the Balloon-borne Large Aperture Submillimeter Telescope (BLAST), at 250, 350, and 500 microns. Since the star-forming galaxies which make up the far-infrared background are expected to trace the underlying dark matter in a biased way, measuring clustering in the far infrared background provides a way to relate star formation directly to structure formation. We test the plausibility of the result by fitting a simple halo model to the data. We derive an effective bias b_eff = 2.2 +/- 0.2, effective mass log(M_eff/M_sun) = 13.2 (+0.3/-0.8), and minimum mass log(M_min/M_sun) = 9.9 (+1.5/-1.7). This is the first robust clustering measurement at submillimeter wavelengths.

http://arxiv.org/abs/0904.1200

Title: Over half of the far-infrared background light comes from galaxies at z >= 1.2

Authors: Mark J. Devlin, Peter A. R. Ade, Itziar Aretxaga, James J. Bock, Edward L. Chapin, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Gaelen Marsden, Peter G. Martin, Philip Mauskopf, Lorenzo Moncelsi, Calvin B. Netterfield, Henry Ngo, Luca Olmi, Enzo Pascale, Guillaume Patanchon, Marie Rex, Douglas Scott, Christopher Semisch, Nicholas Thomas, Matthew D. P. Truch, Carole Tucker, Gregory S. Tucker, Marco P. Viero, Donald V. Wiebe

Journal-ref: Nature, vol. 458, 737-739 (2009) DOI: 10.1038/nature07918

Submillimetre surveys during the past decade have discovered a population of luminous, high-redshift, dusty starburst galaxies. In the redshift range 1 <= z <= 4, these massive submillimetre galaxies go through a phase characterized by optically obscured star formation at rates several hundred times that in the local Universe. Half of the starlight from this highly energetic process is absorbed and thermally re-radiated by clouds of dust at temperatures near 30 K with spectral energy distributions peaking at 100 microns in the rest frame. At 1 <= z <= 4, the peak is redshifted to wavelengths between 200 and 500 microns. The cumulative effect of these galaxies is to yield extragalactic optical and far-infrared backgrounds with approximately equal energy densities. Since the initial detection of the far-infrared background (FIRB), higher-resolution experiments have sought to decompose this integrated radiation into the contributions from individual galaxies. Here we report the results of an extragalactic survey at 250, 350 and 500 microns. Combining our results at 500 microns with those at 24 microns, we determine that all of the FIRB comes from individual galaxies, with galaxies at z >= 1.2 accounting for 70 per cent of it. As expected, at the longest wavelengths the signal is dominated by ultraluminous galaxies at z > 1.

http://arxiv.org/abs/0904.1201

Title: The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) 2006:
Calibration and Flight Performance

Authors: Matthew D. P. Truch, Peter A. R. Ade, James J. Bock, Edward L. Chapin, Mark J. Devlin, Simon R. Dicker, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Gaelen Marsden, Peter G. Martin, Philip Mauskopf, Lorenzo Moncelsi, Calvin B. Netterfield, Luca Olmi, Enzo Pascale, Guillaume Patanchon, Marie Rex, Douglas Scott, Christopher Semisch, Nicholas E. Thomas, Carole Tucker, Gregory S. Tucker, Marco P. Viero, Donald V. Wiebe

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) operated successfully during a 250-hour flight over Antarctica in December 2006 (BLAST06). As part of the calibration and pointing procedures, the red hypergiant star VY CMa was observed and used as the primary calibrator. Details of the overall BLAST06 calibration procedure are discussed. The 1-sigma absolute calibration is accurate to 10, 12, and 13% at the 250, 350, and 500 micron bands, respectively. The errors are highly correlated between bands
resulting in much lower error for the derived shape of the 250-500 micron continuum. The overall pointing error is <5″ rms for the 36, 42, and 60″ beams. The performance of the optics and pointing systems is discussed.

http://arxiv.org/abs/0904.1202

Title: A Bright Submillimeter Source in the Bullet Cluster (1E0657–56) Field Detected with BLAST

Authors: Marie Rex, Peter A. R. Ade, Itziar Aretxaga, James J. Bock, Edward L. Chapin, Mark J. Devlin, Simon R. Dicker, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Gaelen Marsden, Peter G. Martin, Philip Mauskopf, Calvin B. Netterfield, Luca Olmi, Enzo Pascale, Guillaume Patanchon, Douglas Scott, Christopher Semisch, Nicholas Thomas, Matthew D. P. Truch, Carole Tucker, Gregory S. Tucker, Marco P. Viero, Donald V. Wiebe

We present the 250, 350, and 500 micron detection of bright submillimeter emission in the direction of the Bullet Cluster measured by the Balloon-borne Large-Aperture Submillimeter Telescope (BLAST). The 500 micron centroid is coincident with an AzTEC 1.1 millimeter detection at a position close to the peak lensing magnification produced by the cluster. However, the 250 micron and 350 micron emission is resolved and elongated, with centroid positions shifted toward the south of the AzTEC source and a differential shift between bands that cannot be explained by pointing uncertainties. We therefore conclude that the BLAST detection is contaminated by emission from foreground galaxies associated with the Bullet Cluster. The submillimeter redshift estimate based on 250-1100 micron photometry at the position of the AzTEC source is z_phot = 2.9 (+0.6/-0.3), consistent with the infrared color redshift estimation of the most likely Spitzer IRAC counterpart. These flux densities indicate an apparent far-infrared luminosity of L_FIR = 2E13 L_sun. When the amplification due to the gravitational lensing of the cluster is removed, the intrinsic far-infrared luminosity of the source is found to be L_FIR <= 1E12 L_sun, consistent with typical luminous infrared galaxies.

http://arxiv.org/abs/0904.1203

Title: Radio and mid-infrared identification of BLAST source counterparts in the Chandra Deep Field South

Authors: Simon Dye, Peter A. R. Ade, James J. Bock, Edward L. Chapin, Mark J. Devlin, James S. Dunlop, Stephen A. Eales, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Gaelen Marsden, Philip Mauskopf, Lorenzo Moncelsi, Calvin B. Netterfield, Luca Olmi, Enzo Pascale, Guillaume Patanchon, Marie Rex, Douglas Scott, Christopher Semisch, Nicholas Thomas, Matthew D. P. Truch, Carole Tucker, Gregory S. Tucker, Marco P. Viero, Donald V. Wiebe

We have identified radio and/or mid-infrared counterparts to 198 out of 351 sources detected at >= 5 sigma over ~ 9 sq. degrees centered on the Chandra Deep Field South (CDFS) by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) at 250, 350, and 500 microns. We have matched 92 of these counterparts to optical sources with previously derived photometric redshifts and fitted SEDs to the BLAST fluxes and fluxes at 70 and 160 microns acquired with the Spitzer Space Telescope. In this way, we have constrained dust temperatures, total far-infrared/submillimeter luminosities and star formation rates for each source. Our findings show that the BLAST sources lie at significantly lower redshifts and have significantly lower rest-frame dust temperatures compared to submm sources detected in surveys conducted at 850 microns. We demonstrate that an apparent increase in dust temperature with redshift in our sample arises as a result of selection effects. This paper
constitutes the public release of the multi-wavelength catalog of >= 5 sigma BLAST sources contained within the full ~ 9 sq. degree survey area.

http://arxiv.org/abs/0904.1204

Title: BLAST: Resolving the Cosmic Submillimeter Background

Authors: Gaelen Marsden, Peter A. R. Ade, James J. Bock, Edward L. Chapin, Mark J. Devlin, Simon R. Dicker, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Philip Mauskopf, Benjamin Magnelli, Lorenzo Moncelsi, Calvin B. Netterfield, Henry Ngo, Luca Olmi, Enzo Pascale, Guillaume Patanchon, Marie Rex, Douglas Scott, Christopher Semisch, Nicholas Thomas, Matthew D. P. Truch, Carole Tucker, Gregory S. Tucker, Marco P. Viero, Donald V. Wiebe

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) has made one square-degree, deep, confusion-limited maps at three different bands, centered on the Great Observatories Origins Deep Survey South field. By calculating the covariance of these maps with catalogs of 24 micron sources from the Far-Infrared Deep Extragalactic Legacy Survey (FIDEL), we have determined that the total submillimeter intensities are 8.60 +/- 0.59, 4.93 +/- 0.34, and 2.27 +/- 0.20 nW m^-2 sr^-1 at 250, 350, and 500 microns, respectively. These numbers are more precise than previous estimates of the cosmic infrared background (CIB) and are consistent with 24 micron-selected galaxies generating the full intensity of the CIB. We find that more than half of the CIB originates from sources at z >= 1.2. At all BLAST wavelengths, the relative intensity of high-z sources is higher for 24 micron-faint sources than it is for 24 micron-bright sources. Galaxies identified very broadly as AGN by their Spitzer Infrared Array Camera (IRAC) colors contribute 32-48% of the CIB, although X-ray-selected AGN contribute only 7%. BzK-selected galaxies are found to be brighter than typical 24 micron-selected galaxies in the BLAST bands, and contribute 32-42% of the CIB. These data provide high-precision constraints for models of the evolution of the number density and intensity of star-forming galaxies at high redshift.

http://arxiv.org/abs/0904.1205

Title: BLAST: A Far-Infrared Measurement of the History of Star Formation

Authors: Enzo Pascale, Peter A. R. Ade, James J. Bock, Edward L. Chapin, Mark J. Devlin, Simon Dye, Steve A. Eales, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Gaelen Marsden, Philip Mauskopf, Lorenzo Moncelsi, Calvin B. Netterfield, Luca Olmi, Guillaume Patanchon, Marie Rex, Douglas Scott, Christopher Semisch, Nicholas Thomas, Matthew D. P. Truch, Carole Tucker, Gregory S. Tucker, Marco P. Viero, Donald V. Wiebe

We use measurements from the Balloon-borne Large Aperture Sub-millimeter Telescope (BLAST) at wavelengths spanning 250 to 500 microns, combined with data from the Spitzer Infrared telescope and ground-based optical surveys in GOODS-S, to determine the average star formation rate of the galaxies that comprise the cosmic infrared background (CIB) radiation from 70 to 500 microns, at redshifts 0 < z < 3. We find that different redshifts are preferentially probed at different wavelengths within this range, with most of the 70 micron background generated at z < ~1 and the 500 micron background generated at z >~1. The spectral coverage of BLAST and Spitzer in the region of the peak of the background at ~200 microns allows us to directly estimate the mean physical properties (temperature, bolometric luminosity and mass) of the dust in the galaxies responsible for contributing more than 80% of the CIB. By utilizing available redshift information we directly measure the evolution of the far infrared luminosity density and therefore the optically obscured star formation history up to redshift z ~3.

http://arxiv.org/abs/0904.1206

Title: BLAST: The Mass Function, Lifetimes, and Properties of Intermediate Mass Cores from a 50 Square Degree Submillimeter Galactic Survey in Vela (l = ~265)

Authors: Calvin. B. Netterfield, Peter A. R. Ade, James J. Bock, Edward L. Chapin, Mark J. Devlin, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Gaelen Marsden, Peter G. Martin, Phillip Mauskopf, Luca Olmi, Enzo Pascale, Guillaume Patanchon, Marie Rex, Arabindo Roy, Douglas Scott, Christopher Semisch, Nicholas Thomas, Matthew D. P. Truch, Carole Tucker, Gregory S. Tucker, Marco P. Viero, Donald V. Wiebe

We present first results from an unbiased, 50 square degree submillimeter Galactic survey at 250, 350, and 500 microns from the 2006 flight of the Balloon-borne Large Aperture Submillimeter Telescope (BLAST). The map has resolution ranging from 36″ to 60″ in the three submillimeter bands spanning the thermal emission peak of cold starless cores. We determine the temperature, luminosity, and mass of more than a thousand compact sources in a range of evolutionary stages and an unbiased statistical characterization of the population. From comparison with C^18 O data, we find the dust opacity per gas mass, kappa/R = 0.16 cm^2/g at 250 microns, for cold clumps. We find that 2% of the mass of the molecular gas over this diverse region is in cores colder than 14 K, and that the mass function for these cold cores is consistent with a power law with index alpha = -3.22 +/- 0.14 over the mass range 14 M_sun < M < 80 M_sun, steeper than the Salpeter alpha = -2.35 initial massfunction for stars. Additionally, we infer a mass dependent cold core lifetime of tau(M) = 4E6 (M/20 M_sun)^-0.9 years — longer than what has been found in previous surveys of either low or high mass cores, and significantly longer than free fall or turbulent decay time scales. This implies some form of non-thermal support for cold cores during this early stage of star formation.

http://arxiv.org/abs/0904.1207

You can find a lot more detailed information on the dedicated BLAST website.

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