Archive for Herschel Space Observatory

Merging Galaxies in the Early Universe

Posted in The Universe and Stuff with tags , , , , on November 14, 2017 by telescoper

I just saw this little movie circulated by the European Space Agency.

The  source displayed in the video was first identified by European Space Agency’s now-defunct Herschel Space Observatory, and later imaged with much higher resolution using the ground-based Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. It’s a significant discovery because it shows two large galaxies at quite high redshift (z=5.655) undergoing a major merger. According to the standard cosmological model this event occurred about a billion years after the Big Bang. The first galaxies are thought to have formed after a few hundred million years, but these objects are expected to have been be much smaller than present-day galaxies like the Milky Way. Major mergers of the type seen apparently seen here are needed if structures are to grow sufficiently rapidly, through hierarchical clustering, to produce what we see around us now, about 13.7 Gyrs after the Big Bang.

The ESA press release can be found here and for more expert readers the refereed paper (by Riechers et al.) can be found here (if you have a subscription to the Astrophysical Journal or for free on the arXiv here.

The abstract (which contains a lot of technical detail about the infra-red/millimetre/submillimetre observations involved in the study) reads:

We report the detection of ADFS-27, a dusty, starbursting major merger at a redshift of z=5.655, using the Atacama Large Millimeter/submillimeter Array (ALMA). ADFS-27 was selected from Herschel/SPIRE and APEX/LABOCA data as an extremely red “870 micron riser” (i.e., S_250<S_350<S_500<S_870), demonstrating the utility of this technique to identify some of the highest-redshift dusty galaxies. A scan of the 3mm atmospheric window with ALMA yields detections of CO(5-4) and CO(6-5) emission, and a tentative detection of H2O(211-202) emission, which provides an unambiguous redshift measurement. The strength of the CO lines implies a large molecular gas reservoir with a mass of M_gas=2.5×10^11(alpha_CO/0.8)(0.39/r_51) Msun, sufficient to maintain its ~2400 Msun/yr starburst for at least ~100 Myr. The 870 micron dust continuum emission is resolved into two components, 1.8 and 2.1 kpc in diameter, separated by 9.0 kpc, with comparable dust luminosities, suggesting an ongoing major merger. The infrared luminosity of L_IR~=2.4×10^13Lsun implies that this system represents a binary hyper-luminous infrared galaxy, the most distant of its kind presently known. This also implies star formation rate surface densities of Sigma_SFR=730 and 750Msun/yr/kpc2, consistent with a binary “maximum starburst”. The discovery of this rare system is consistent with a significantly higher space density than previously thought for the most luminous dusty starbursts within the first billion years of cosmic time, easing tensions regarding the space densities of z~6 quasars and massive quiescent galaxies at z>~3.

The word `riser’ refers to the fact that the measured flux increases with wavelength from the range of wavelengths measured by Herschel/Spire (250 to 500 microns) and up 870 microns. The follow-up observations with higher spectral resolution are based on identifications of carbon monoxide (CO) and water (H20) in the the spectra, which imply the existence of large quantities of gas capable of fuelling an extended period of star formation.

Clearly a lot was going on in this system, a long time ago and a long way away!

 

Orion Nebula (Herschel, after Turner)

Posted in Art, The Universe and Stuff with tags , , , on September 6, 2013 by telescoper

I stumbled across this wonderful image (and associated description) yesterday and thought I’d share it. It’s a region of the Orion Nebula (which is located in the  Midlands region of Orion’s “sword”, i.e. the long thing hanging down below his belt).  It’s a turbulent region of dust and gas in which stars are forming. This image was taken in the far-infrared part of the spectrum by the Herschel Space Observatory, which is now defunct but much data remains to be analysed. Because the image was taken at wavelengths much longer than optical light, the colours are obviously “false”. I don’t work on star formation so I tend to see images like this just as beautiful things to be enjoyed for themselves rather than as a subject for scientific research. In fact, I have no difficulty at all in describing this picture as a work of art, slightly reminiscent of the cloudscapes and seascapes of  J.M.W Turner in that it is, at the same time, both a representation of a natural phenomenon and  an abstract creation that transcends it. You can click on the image to make it larger…

Orion_A

UPDATE: I see that someone else has thought of the parallel with Turner!

Lines on the Death of Herschel

Posted in Poetry, The Universe and Stuff with tags on April 30, 2013 by telescoper

So farewell, then,
Herschel
Space
Observatory.

You were named after
William Herschel,
Who lived
During the reign of
George III.
The mad King
Who went blind,
Then died.

You went blind
Then died.
But there the
Similarity
Ends.

You ran out
Of Helium;
He had no
Need of He.

And he was neither
In Space
Nor an
Observatory,
So forget
It.

by Peter Coles (aged 49 11/12).

HFLS3: the earliest Starburst yet!

Posted in The Universe and Stuff with tags , , , , on April 24, 2013 by telescoper

Once again I’ve spent all day engaged in the enjoyable but exhausting task of interview for new faculty positions, which means that I haven’t really got time for a proper blog today. What I can do, however, is shamelessly rip off a nice press release produced by the good folks here at the University of Sussex about a discovery that has been attracting a lot of press coverage since it was published last week in Nature; the paper is also available on the arXiv. If you’ve followed this blog for a while you will know than when I was at Cardiff I got interested in a large project called the Herschel Atlas survey, which is a large area galaxy survey carried out using the Herschel Space Observatory. This result is not from Herschel ATLAS but from a complementary deeper survey called Hermes, also performed using the Herschel Space Observatory and it is of a very distant and very bright starburst galaxy (a type of galaxy which, as its name suggests, in which stars are forming at a much higher rate than a “normal” galaxy).

Incidentally, although Herschel is now extremely short of the Helium it needs to keep itself cool, it is still making observations running on empty, as it were.

Anyway, that’s all I’ve got time to write. The rest is just copied from the press release I mentioned…

–o–

University of Sussex astronomers using the Herschel Space Observatory are part of an international team that has discovered a distant star-forming galaxy that challenges the current theories of galaxy evolution.

Seen when the Universe was less than a billion years old (880 million years) the galaxy, known only as “HFLS3”, is forming stars at a much faster rate than should be possible according to existing predictions. In the infant Universe, galaxies should have been forming stars at a much slower rate than is observed in HFLS3.

HFLS3 is so distant that the light we see from it has taken 13 billion years to get to Earth.

The Herschel observatory1 has been surveying the distant cosmos and finding hundreds of thousands of distant galaxies. Images produced by Herschel show how fast these distant galaxies are forming stars.

By determining the ages of the galaxies, astronomers have been building up a cosmic timeline of star formation, searching for when the first massive galaxies started churning out stars.

University of Sussex PhD student Peter Hurley, Dr Isaac Roseboom, Dr Anthony Smith, Dr Lingyu Wang and Professor Seb Oliver, who leads the HerMES2 survey that found the galaxy, analysed data from Herschel and built the HFLS3 galaxy as a computer model to discover what conditions are like in the galaxy.

Peter says: “The stars being born in HFLS3 heat up the surrounding material within the galaxy. This material contains gas molecules such as carbon monoxide and water, which emit their own unique signatures when heated. By comparing the telescope observations with models, we can gain a better understanding of the conditions within this extreme galaxy.”

The galaxy “HFLS3” was first seen as a small red dot in the Herschel images, and its colour is what first intrigued the team because red galaxies might be very distant.

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The galaxy HFLS3 as revealed by Herschel and further ground-based telescope observations. Images: ESA/Herschel/HerMES/IRAM/GTC/W.M. Keck Observatory

Further investigations using optical and near-infrared telescopes the Gran Telescopio Canarias in the Canary Islands and the Keck Telescope in Hawaii helped to rule out any other effects that might cause the HFLS3 galaxy to look so bright.

It was observations with radio and millimetre-wave telescopes, such as the Plateau de Bure Interferometer in the French Alps, which determined that this tiny galaxy, only around one twentieth the size of our Milky Way, is seen at such an immense distance. These additional observations also showed that HFLS3 is incredibly rich in carbon, nitrogen and oxygen, forming compounds such as carbon monoxide, water and ammonia. These compounds reveal the physical processes at work in this distant galaxy.

Combined with the Herschel observations, these measurements allow the astronomers to deduce that this tiny star factory is producing stars around two thousand times faster than our own Milky Way, making it a type of galaxy known as a “starburst”. Environments like this do not exist on galaxy-wide scales in the Universe today.

Professor Oliver says: “We’ve shown that Herschel data can find these extreme examples. “The next step is to sift through the Herschel data more carefully, and try to deduce just how common such galaxies were in the early Universe. I am also very pleased that a Sussex PhD student has been able to make an important contribution to this work.”

Jamie Bock (Caltech, USA), who co-leads the HerMES survey with Professor Oliver, says: “This galaxy is just one spectacular example, but it’s telling us that early star formation like this is possible,” explains Jamie Bock, Caltech, and one of the leaders.

Dominik Riechers (Cornell University, USA), who led the HFLS3 study, says: “Looking for the first examples of these massive star factories is like searching for a needle in a haystack. We were hoping to find a galaxy at such vast distances, but we could not expect that they even existed that early on in the Universe.”

The Heat Death of Herschel

Posted in The Universe and Stuff with tags , , , , on March 13, 2013 by telescoper

Most of the astronomers who read this blog will have heard the news that the Herschel Space Observatory is running out of the Helium that it has been using to keep it cool enough (~1.4K) to be sensitive to the far-infra-red radiation emitted by very distant objects.

There’s a gallery of wonderful images obtained by Herschel since it was launched in 2009 at the news item linked to above, but my favourite is one of the least photogenic:

_66205134_goodsn_3colour_cropped

Many of these fuzzy blobs correspond to immensely distant galaxies; what we see is starlight from very young stars absorbed by vast amounts of cosmic dust and then re-radiated in the infra-red. Understanding these sources is decidedly non-trivial and it will take many years to get all the information out that is hidden in images like this.

Anyway, one thing worth pointing out here is that what is going on now with Herschel is not some kind of failure. Quite the contrary, in fact. The original mission lifetime was planned to be three years, and Herschel has now been operating for nine months longer than that. The supply of Helium was always going to be the limiting factor as the spacecraft operates at the second Lagrange point of the Earth-Sun system, which is almost a million miles away and thus too far to be replenished. When the Helium does run out, Herschel will rapidly heat up to the point where its detectors are swamped. It will then be blind.

I was at this point going to make a cheap joke to the effect that after years on its own in the dark preoccupied with images of heavenly bodies, it was entirely predictable that Herschel would go blind. But I decided not to. I’ll save that kind of off-colour remark for Twitter…

ps. Coincidentally, on this day (March 13th) in 1781,  William Herschel  discovered the planet Uranus. The telescope is named in Herschel’s honour because he was also the first person to demonstrate the existence of infra-red radiation.

Herschel at the Royal Society

Posted in The Universe and Stuff with tags , , , on July 2, 2012 by telescoper

I found this nice little video about the forthcoming Royal Society Summer Science Exhibition which opens tomorrow at the Royal Society’s premises in Carlton House Terrace in London.

Astronomers from Cardiff University are heavily involved in one of the exhibits related to the Herschel Telescope – To infrared and beyondI’m actually doing a couple of shifts on the Herschel stand myself, on  Thursday and Friday afternoons, as well as during a posh black tie  “soirée” on Thursday evening. Last time I attended such an event (in 2009) was during a heat wave, which made the soirée an uncomfortably sticky experience, but the forecast suggests the weather might be a bit different this time round…

The Eagle Nebula (as seen by Herschel)

Posted in Poetry, The Universe and Stuff with tags , , , on January 17, 2012 by telescoper

It’s been a while since I posted anything from the Herschel Space Observatory, but here’s a stunning image I just saw on the BBC website which will more than rectify that omission. This is the Eagle Nebula, a much-studied object in terms of the optical light it emits, but this is a remarkable picture taken in the far-infrared part of the spectrum.

For more details, see here.

There’s much more to astronomy than looking at pretty pictures, but the opportunity to stare at things like this is definitely one of the perks of the job. It makes me think of Tennyson’s Poem, The Eagle

He clasps the crag with crooked hands;
Close to the sun in lonely lands,
Ring’d with the azure world, he stands.

The wrinkled sea beneath him crawls;
He watches from his mountain walls,
And like a thunderbolt he falls.

The Day After…

Posted in The Universe and Stuff with tags , , , on December 14, 2011 by telescoper

Yesterday was a memorable day for more reasons than the outbreak of Higgs-teria I blogged about. The main event was in fact the PhD examination of my student Jo Short. Being the supervisor, I didn’t actually attend the examination in person but did get to have lunch with the Chair and other examiners, including external examiner Andrew Jaffe from Imperial College, who blogs at Leaves on the Line.

After lunch the Examiners, Chair and candidate disappeared into the special room we keep for such occasions (complete with thumbscrews, etc) and I went back to my office to wait it out while Jo was grilled. I always feel a bit protective towards my PhD students, and a viva voce examination always brings back painful memories of the similar ordeal I went through twenty-odd years ago. Although I had every confidence in Jo, I was a bit nervous sitting in my office wondering how it was going. However, this is something a PhD candidate has to go through on their own, a sort of rite of passage during which the supervisor has to stand aside and let them stand up for their own work.

About 90 minutes after the viva started I remembered that I had to pick up some medication from a chemist, so braved the inclement weather to do that.  Yesterday, incidentally, threw an extraordinary range of weather at us: hail, thunder, gales and dark apocalyptic clouds. When I returned the examination was already over; Jo passed with minimal corrections to be made. My nerves clearly weren’t justified. Congratulations Dr Short!

Caught on the hop by the fact that the viva finished in just over 2 hours, I then had to mobilize the obligatory champagne which was chilling in a fridge belonging to the Astronomy Instrumentation Group. Worse, a team of PhD students which had been dispatched to buy celebratory gifts hadn’t returned with the goodies by the time we opened the bubbly. Nevertheless, an appropriate celebration was eventually held in the department, followed – so I’m told – by an evening of revelry in the town. I didn’t go to the latter, as I’m far too old for that sort of thing.

By the way, Jo’s thesis is partly about the analysis of the pattern of temperature variations in the cosmic microwave background and partly about modelling galaxy clustering revealed by the Herschel Space Observatory and she’s staying on at Cardiff on a research fellowship.

P.S. Our genial external was last seen getting into a taxi to get to the station and thence back to London. I assume he got home safely…

P.P.S. For the sake of complete disclosure I should admit that I wrote this blog post while chairing another viva…

The Curious Case of the Twisted Ring

Posted in The Universe and Stuff with tags , , , , , , , on July 21, 2011 by telescoper

Just time for a quickie this morning, prompted by the appearance of our own Professor Matt Griffin on the Today programme on BBC Radio 4 earlier on talking about newly published results from the Herschel Space Observatory. I didn’t hear it live as I’m strictly a Radio 3 person, but it must have made a pleasant change from stories about the imminent collapse of the euro and continuing extraordinay revelations about widespread corruption involving the British media, police force and political establishment. Among all this doom and gloom it’s nice to hear news of something that’s actually successful.

Anyway, the news from Herschel is that it has unveiled a ring structure in the centre of our Milky Way galaxy. The ribbon of gas and dust is more than 600 light years across and appears to be twisted, for reasons which have yet to be explained. The origin of the ring could yield important clues about the history of the Milky Way.

Warmer gas and dust from the Centre of our Galaxy is shown in blue in the  image below, while the colder material appears red. The ring, in yellow, is made of gas and dust at a temperature of just 15 degrees above absolute zero. The bright regions are denser, and include some of the most massive and active sites of star formation in our Galaxy.

and here it is with the curious ring drawn on with crayons:

The central region of our Galaxy is dominated by an elongated structure, rather like a bar, which stirs up the material in the outer galaxy as it rotates over millions of years and is probably connected with the spiral structure seen in the disk of the Milky Way. The ring seen by Herschel lies right in the middle of this bar, encircling the region which harbours a super-massive black hole at the centre of our galaxy. The ring of gas is twisted, so we see two loops which appear to meet in the middle. These are seen in yellow in the image above, tilted slightly such that they run from top-left to bottom-right. Secondly, it seems to be slightly offset from the very centre of our Galaxy. The reason for the ring’s twist and offset are unknown, but understanding their origin may help explain the origin of the ring itself. Computer simulations indicate that bars and rings such as those we see in the centre of our Galaxy can be formed by gravitational interactions, either within the Milky Way itself or between it and the nearby Andromeda galaxy, M31.

For the experts, and others interested, the scientific paper containing these results can be found here.

Finding Gravitational Lenses, the Herschel Way…

Posted in The Universe and Stuff with tags , , , , , , on November 4, 2010 by telescoper

It’s nice to have the chance to blog for once about some exciting astrophysics rather than doom and gloom about budget cuts. Tomorrow (5th November) sees the publication of a long-awaited article (by Negrello et al.)  in the journal Science (abstract here) that presents evidence of discovery of a number of new gravitational lens systems using the Herschel Space Observatory.

There is a press release accompanying this paper on the  Cardiff University website, and a longer article on the Herschel Outreach website, from which I nicked the following nice graphic (click on it for a bigger version).

This shows rather nicely how a gravitational lens works: it’s basically a concentration of matter (in this case a galaxy) along the line of sight from the observer to a background source (in this case another galaxy). Light from the background object gets bent by the foreground object, forming multiple  images which are usually both magnified and distorted. Gravitational lensing itself is not a new discovery but what is especially interesting about the new results are that they suggest a much more efficient way of finding lensed systems than we have previously had.

In the past they have usually been found by laboriously scouring optical (or sometimes radio) images of very faint galaxies. A candidate lens (perhaps a close-set group of images with similar colours), then this candidate is followed up with detailed spectroscopy to establish whether the images are actually all at the same redshift, which they should be if they are part of a lens system. Unfortunately, only about one-in-ten of candidate lens systems found this way turn out to be actual lenses, so this isn’t a very efficient way of finding them. Even multiple needles are hard to find in a haystack.

The new results have emerged from a large survey, called H-ATLAS, of galaxies detected in the far-infrared/submillimetre part of the spectrum. Even the preliminary stages of this survey covered a sufficiently large part of the sky – and sufficiently many galaxies within the region studied – to suggest  the presence of a significant population of galaxies that bear all the hallmarks of being lensed.

The new Science article discusses five surprisingly bright objects found early on during the course of the H-ATLAS survey. The galaxies found with optical telescopes in the directions of these sources would not normally be expected to be bright at the far-infrared wavelengths observed by Herschel. This suggested that the galaxies seen in visible light might be gravitational lenses magnifying much more distant background galaxies seen by Herschel. With the relatively poor resolution that comes from working at long wavelengths, Herschel can’t resolve the individual images produced by the lens, but does collect more photons from a lensed galaxy than an unlensed one, so it appears much brighter in the detectors.

 

Detailed spectroscopic follow-up using ground-based radio and sub-millimetre telescopes confirmed these ideas :  the galaxies seen by the optical telescopes are much closer, each ideally positioned to create gravitational lenses.

These results demonstrate that gravitational lensing is probably at work in all the distant and bright galaxies seen by Herschel. This in turn, suggests that in the full H-ATLAS survey might provide huge numbers of gravitational lens systems, enough to perform a number of powerful statistical tests of theories of galaxy formation and evolution. It’s a bit of a cliché to say so, but it looks like Herschel will indeed open up a new window on the distant Universe.

P.S. For the record, although I’m technically a member of the H-ATLAS consortium, I was not directly involved in this work and am not among the authors.

P.P.S. This announcement also gives me the opportunity to pass on the information that all the data arising from the H-ATLAS science demonstration phase is now available online for you to play with!


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