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On seeing the Euclid launch

On seeing the Euclid launch

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In July, I had the great luck to visit the Kennedy Space Flight Center to see the launch of the Euclid satellite. I wrote this a few days after the launch, but with the great amount of work that we have all been doing since then, I have not had time to publish this! I was thinking I had better get caught up…

My trip to Florida started inauspiciously enough, with a text message telling me that my flight to Newark, the first leg of my journey, had been delayed. This meant that I would miss my connection to Orlando. At CDG the united staff told me that, although they couldn’t rebook my flight from Paris, don’t worry, in Newark they will look after you. I imagined disembarking from the plane and walking right to the smiling United representative at the service desk who would immediately put me on the next available flight. The reality was a four-hour wait in the line-up at Newark until finally a very helpful lady booked me on a flight to Orlando the next morning. I arrived in the humid Florida heat on Friday with enough time to pick up my tickets and those of my colleagues. I will pass in silence over the night spent in a hotel in the grey post-industrial suburbs of New Jersey.

I admit that I had a certain ‘frisson’ seeing the signs for ‘Kennedy Space Flight Center’ (KSFC) as I drove away from Orlando airport. As a child in Ireland in the 1970s I wrote to KSFC and asked them to send me stuff about space and planets. Soon enough, a big wad of old press releases as well as some nice colour pictures of planets arrived from America in a big yellow envelope. It was wonderful. I couldn’t understand why more people were not interested in astronomy given the Universe was so large and the Earth was so small. And so now, 40 years later, I was on a highway heading right to KSC. Soon enough, I was flying over a large river inlet and in the distance I could see what I knew was the famous Vehicle Assembly Building, the largest building in the world. But right now, I was not going to KSC, I was only going to the hotel to get the tickets…

The next morning, I left the hotel at 07:20. The launch was scheduled for 11:12AM, but I knew that My bag was full of cameras and factor 50 sunscreen. I had a big hat I bought at the surf shop near my hotel, ready for the intense heat and light of a summer morning in Florida. I picked up a colleague at his nearby hotel.

Although we had left early, there were already many people at Kennedy for the launch. It was blisteringly hot, and the sun shone brightly in a blue sky without clouds. Although I have been working on the Euclid project for more than a decade and have been to every consortium meeting (except one), there were many people I had never seen before.

Soon enough, we left on the first bus carrying everyone to the bleachers at banana creek, a prime viewing location across the water from the launch towers. The bleachers, however, had not an inch of shade, and it was more than an hour until the launch; no question of staying outside. But next to the bleachers was the Saturn V Apollo building, and we spent a good hour there looking at this impressive space hardware from the past. Soon it was time to go outside again

At the bleachers, everyone was finding their places. There was blinding heat and light. To the right, there was a big screen relaying the SpaceX/ESA livestream, and a local commentator provided us some additional context. I stared out at the horizon at where the Euclid will soon leave the Earth. Confusingly, there were several different launch towers.

Waiting for the Euclid Launch

And suddenly, we were only a few minutes before launch. We were in the bleachers. I had promised to do a livestream with IAP auditorium where everyone was gathered to watch the launch. I put in my AirPods and my colleague Amadine tried to film me with my iPhone. There was so blinding light everywhere it was impossible to see the screen, but I could hear the questions from Paris and I tried to formulate some intelligent answers.

We were in the final minutes before the countdown. No sign of a hold or a delay. There were no clouds in the sky. We were told there was a delay between the livestream and the real world, a few seconds, not much but enough to make everyone chanting countdown pointless. We didn’t know the real-world number of minutes left. Suddenly, there was an enormous cloud on the horizon, low down, and rising from the clouds we could see the Falcon 9 rocket atop a bright orange-yellow flame. It was one of the brightest things I have ever seen. But at first it was completely silent as the rocket arched up into the sky. Then the sound came, a great rolling rumbling wave of sound energy. My cheap straw hat vibrated in time to the roar of the nine merlin rocket engines. Clearly, it takes a lot of energy to get a one-ton rocket to L2, I thought to myself.

I was transfixed. In the bag at my feet I had my two Leica cameras, I had my telephone and a Ricoh compact camera too, but I didn’t want to do anything but look at this bright orange candle as it disappeared into the cloudless sky. On the callout from the screen we heard ‘maxq’ indicating the rocket had passed through the zone of maximum aerodynamic pressure. And then, it was gone, and there was finally just a cloud in the sky, a cloud of water vapour made by the Falcon 9 rocket.

The livestream from ESA and SpaceX continued. We saw the booster coming back, landing on the drone ship. There in orbit was a short coast phase and the second stage ignited again. By this time, all the public had left and there were only a few of us in the bleachers or sheltering nearby. Then, on the “jumbotron” — the big screen they have there — we saw Euclid deploy, the silvery yellow foil catching the sunlight as at it separated from the SpaceX second stage. But still, the story was not over. Was the satellite alive and communicating with the Earth? Then finally on the screen we saw the first signal from the spacecraft. Euclid was alive and heading to L2. And the real work would start very soon.

Waiting for the signal from Euclid at KFC
Euclid in the clean room
The road to the space coast (looking back on the ideas that led to Euclid)

The road to the space coast (looking back on the ideas that led to Euclid)

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On Florida’s Space Coast, the Euclid satellite is undergoing the final preparations for launch on a Falcon 9 rocket next Saturday, July 1st at 11:12 EDT. Although the Euclid mission was approved by ESA in 2011, the origins of the project date back more than a decade before that, starting with the realisation that the expansion of the Universe is accelerating.

In cinema, great discoveries are usually accompanied by the leading lights throwing their hands in the air and exclaiming, “This changes everything!” But in real life, scientists are cautious, and the first reaction to any new discovery is usually: is there a mistake? Is the data right? Did we miss anything? You need to think carefully about finding the right balance between double-checking endlessly (and getting scooped by your competitors) or rushing into print with something that is wrong. At the end of the 1990s, measurements of distant supernovae suggesting the accelerated expansion of the Universe were initially greeted by scepticism.

Conceptually, what those measurements were saying was simple: the further away an object is, the faster it is receding from us. Edwin Hubble’s early observations of galaxies demonstrated that there was a straight-line relationship between the distance of an object and the speed of movement. The most simple explanation (although one that scientists took a while to accept) was that the Universe was expanding.

Over the next few decades, researchers embarked on a long quest to find different classes of objects for which they could estimate distances. Supernovae were one of the best: it turned out that if you could measure how the brightness of supernovae changed with time, you could estimate their distances. You could then compare how the distance depended on redshift, which you could measure with a spectrograph. Wide-field cameras on large telescopes allowed astronomers to find supernovae further and further away, and by the end of the 90s, samples were large enough to detect the first tiny deviations from Hubble’s simple straight-line law. The expansion was accelerating. The origin of the physical process of expansion was codified by “Lambda”. Or “dark energy”.

First measurements of distant supernovae from two teams. The most distant measurements are above the straight-line measurements by ~20%.

But those points on the right-hand side of the graphs which deviated from Hubble’s straight-line law had big error bars. Everyone knew that supernovae were fickle creatures in any case, subject to a variety of poorly understood physical mechanisms that could mimic the effect that the observers were reporting.

Initially, there was a lot of resistance to this idea of an accelerating Universe, and to dark energy. Nobody wanted Lambda. Not the theorists, because there were no good theoretical explanations for Lambda. And not the simulators, because Lambda unnecessarily complicated their simulations. And not even the observers, because it meant that every piece of code used to estimate physical properties of distant galaxies had to be re-written (a lot of boring work). Meanwhile, the supernovae measurements became more robust and the reality of the existence of Lambda become harder and harder to avoid. But what was it? It was hard to get large samples of supernovae, what other techniques could be used to discover what Lambda really is? Soon, measurements of the cosmic microwave background indicated that Lambda was indeed the preferred model, but because the acceleration only happens at relatively recent epochs in the Universe, microwave background observations only have limited utility here.

Meanwhile, several key instrumental developments were taking place. At the Canada France Hawaii Telescope and other observatories, wide-field cameras with electronic detectors — charge coupled devices, or CCDs — were being perfected. These instruments enabled astronomers for the first time to survey wide swathes of the sky and measure the positions, shapes and colours of tens of thousands of objects. At the same, at least two groups were testing the first wide-field spectrographs for the world’s largest telescopes. Fed by targets selected from the new wide-field survey cameras, these instruments allowed the determination of the precise distances and physical properties of tens of thousands of galaxies. This quickly led to many new discoveries of how galaxies form and evolve. But these new instruments would also allow us to return to the still-unsolved nature of the cosmic acceleration, using a variety of new techniques which were first tested with these deep, wide-field surveys.

In the 1980s, observations of galaxy clusters with CCD cameras led to the discovery of the first gravitational arcs. These are images of distant galaxies which are, incredibly, magnified by the passage of light near the cluster. The deflection of light by mass is one of the key predictions of Einstein’s theory of general relativity. The grossly distorted images can only be explained if a large part of the mass of the cluster is concealed in invisible or ‘dark’ matter. However, in current models of galaxy formation, the observed growth of structures in the Universe can only be explained if this dark matter is distributed throughout the Universe and not only in the centres of galaxy clusters. This means also that even the shapes of galaxies of the ‘cosmic wallpaper’ throughout the night sky should be very slightly correlated, as light rays from these distant objects pass close to dark matter everywhere in the Universe. The effect would be tiny, but it should be detectable.

Simulation of the passage of light rays through the Universe, passing close to dark matter (S. Colombi, IAP).

Around the world, several teams raced to measure this effect in new wide-field survey camera data. The challenges were significant: the tiny effect required a rigorous control of every source of instrumental error and detailed knowledge of telescope optics. But by the early 2000s, a few groups had measured the ”correlated shapes” of faint galaxies. They also showed that this measurement could be used to constrain how rapidly structures grow in the Universe. At the same time, other groups, using the first wide field spectroscopic surveys, found that measurements of galaxy clustering could be used to independently constrain the parameters of the cosmological model.

Halfway through the first decade of the 21st century, it was beginning to become clear that both clustering combined with gravitational lensing could be an excellent technique to probe the nature of the acceleration. Neither method was easy: one required very precise measurements of galaxy shapes, which was very hard to do with ground-based surveys which suffered from atmospheric blurring; the other required spectroscopic measurements of hundreds of thousands of galaxies. And both techniques seemed highly complementary to supernovae measurements.

In 2006, the report from a group of scientists from Europe’s large observatories and space agencies charted a way forward to understand the origin of the acceleration. Clearly, what was needed was a space mission to provide wide-field high-resolution imaging over the whole sky to measure the shapes, coupled with an extensive spectroscopic survey. Both these ideas were submitted as proposals for two satellites: one would provide the spectroscopic survey (SPACE) and the other would provide the high-resolution imaging (Dune). The committee, finding both concepts compelling, asked the two teams to work together to design a single mission, which would become Euclid. In 2012, the mission was formally approved.

Euclid in the clean room
Euclid in the clean room at Thales Alenia

Euclid aims to make the most precise measurement ever of the geometry of the Universe and to derive the most stringent possible constraints on the parameters of the cosmological model. Euclid uses two methods: galaxy clustering with the spectrograph and imager NISP (sensitive to dark energy) and gravitational lensing with the imager VIS (sensitive to dark matter). Euclid‘s origins in ground-based surveys makes it unique. Euclid aims to make a survey of the whole extragalactic sky over six years. But unlike in ground-based surveys, no changes can be made to the instrument after launch. After launch, Euclid will travel to the remote L2 orbit, one of the best places in the solar system for astronomy, to begin a detailed instrument checkout and prepare for the survey.

I have been involved in the team which will process VIS images for more than a decade. The next few weeks will be exciting and stressful in equal measures. VIS is the “Leica Monochrom” of satellite cameras: there is only one broad filter. The images will be in black-and-white. It will (mostly) not make images deeper than Hubble or James Webb: Euclid‘s telescope mirror is relatively modest (there are some Euclid deep fields, but that is another story). But to measure shapes to the required precision to detect dark matter, every aspect of the processing must be rigorously controlled.

VIS images will cover tens of thousands of square degrees. Over the next few years, our view of the Universe will dramatically snap into high resolution. That, I am certain, will reveal wonders. Those images will be one of the great legacies of Euclid, together with a much deeper understanding of the cosmological model underpinning the Universe that will come from them and the data from NISP.

This Thursday, I’ll be travelling to Florida to see Euclid start its journey to its L2 orbit for myself. I’ll be awaiting anxiously with many of my colleagues for our first glimpse of the wide-field, high-resolution Universe that will arrive a few weeks later.

Looking into (the) COSMOS with the James Webb Space Telescope

Looking into (the) COSMOS with the James Webb Space Telescope

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With the imminent launch of JWST — we hope! — I am resurfacing an article I wrote earlier this year which appeared in a different form on the IAP front page. Next year I will be giving a public conference about this which will be streamed live.

Astronomers learned to read the patterns of stars in the starry night skies as clues to the shape of our own Milky Way. Powerful telescopes soon showed that galaxies themselves were spread out across the sky in a pattern that holds profound clues to the nature and eventual fate of the Universe itself. This is the history of astronomy: with each new instrument, scientists take a step towards a better understanding of our Universe. Very soon, using the James Webb Space Telescope (JWST), an international team of astronomers — my friends in the COSMOS project — will map out a vast unexplored region of the very distant Universe. A key prediction of current theories of the formation of the Universe is that stars and galaxies form hot ionised bubbles of gas in the early Universe. With JWST we will see for the first time the imprint of these bubbles on the large-scale distribution of the very first stars and galaxies. They will also help us to understand how mysterious dark matter helps galaxies to form at the earliest times.

Bubbles in the early Universe (from A. Loeb)

Over the past three decades, the Hubble Space Telescope has opened up vistas of the distant Universe only dimly glimpsed by ground-based observatories. However, charting out how galaxies are linked together across the sky seemed at first like an impossible task for Hubble. The telescope’s cameras can only see a tiny part of the sky in each exposure. But a team of astronomers ambitiously used Hubble to survey a region of the sky larger than the full moon — now known as the COSMOS field — making it the latest ever contiguous patch of the sky covered by Hubble. Since then, thousands of scientific papers have delved deep into the COSMOS field, drawing a detailed picture of how galaxies, dark matter, gas, and dust interact on large scales and how they have changed over cosmic time. Since those first Hubble observations, COSMOS has been covered by every major telescope and this data has been shared in a remarkably open and productive collaboration between all the world’s astronomers.

The original COSMOS Advanced Camera for Surveys HST mosaic

The COSMOS catalogues have become an essential reference point for the evolution of galaxies over cosmic time and an invaluable starting point to ask any new questions about the Universe. The papers describing them are among the most highly cited in astronomy. COSMOS catalogues have also played a crucial role in preparing for Esa’s Euclid mission.

Of course, astronomers would always like to see further. Data from COSMOS has hinted at another Universe of very distant, massive galaxies just out of reach of current surveys. The finite speed of light is a wonderful time-machine which means that these most distant objects lie, in fact, at the very beginnings of the Universe. But the expansion of the Universe means their light becomes redder and redder as it speeds towards us. To see so very far back, one needs a not only a telescope with a mirror large enough to collect these lonely photons arriving from the edge of the Universe — but also one sensitive to the infrared light bringing messages from these distant galaxies. An even greater challenge is that every ordinary object also emits infrared photons; these would drown out the faint signal from such distant galaxies. To detect this ancient light, the telescope must be cooled to a few degrees above absolute zero and placed far from terrestrial sources. The ten-billion-dollar James Webb Space Telescope (JWST), with its golden 6.5 meter foldable mirror, due to be launched and sent to one of the coldest places in the solar system, is just such a telescope. It is optimised for the study of these faint distant objects. A single exposure from JWST will see deeper than the decade-long ground-based infrared surveys that we in the COSMOS team have been carrying out.

Let’s hope that it will look like this in a few months…

JWST is a remarkable instrument, perhaps the most sensitive telescope ever constructed. Its cameras can record light from objects infinitely fainter than anything we have ever observed before. But where do you point such a beautiful and sensitive machine if it is looking deep into a country that no-one has ever visited before? The best thing to do, right at the start, is to survey a wide swath of this new territory to guide future scientist-explorers. But once again, such a survey seemed an impossible task with the tiny field-of-view of the JWST cameras. Nevertheless, we proposed a highly ambitious program — now called COSMOS-Web — to cover one third of the COSMOS field with JWST’s infrared and near-infrared cameras. Such a survey would require more than 200 hours of observations, an enormous amount for the highly competitive first year of Webb’s operations. Astronomers around the world requested more than four times the amount of time than were actually available. The results of this competition were announced earlier this year: the COSMOS-Web proposal was accepted, making it the largest survey to be carried out during the first year of JWST’s operations. We call it COSMOS-Web because it will map out the web of large-scale-structure of the Universe at the earliest epochs.

Simulated image of the JWST-COSMOS field

Our program comprises 206 hours with JWST’s NIRCAM instrument and 80 hours taken simultaneously with the longer-wavelength MIRI camera. Together, in COSMOS-Web these instrument will produce a new map of the very distant Universe. All data will be public. The new data will contain tens of thousands of very faint and distant galaxies, signposts for follow-up observations with JWST’s other very sensitive instruments. Astronomers will see, for the first time, the structure and form of galaxies in the early universe. And we will see, we hope, things we do not expect to see. Over the years observations in COSMOS has turned up countless interesting and peculiar objects and I am certain JWST observations will continue this tradition!

Olivier Le Fèvre

Olivier Le Fèvre

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It was the winter of 1998. I was reaching the end of my thesis in Durham, England, and I knew it was time to start looking for a new city to live in, a new place to go. By this point in my life I’d already spent almost three years in North America (Socorro, New Mexico, and Victoria, BC) and six years in England (Durham and Manchester), and I knew that I really didn’t want to live in those kinds of of places any more, I knew that they weren’t for me. But was there any place in Europe that did the kind of science I wanted to do, what I had done in Canada and England? By that I meant surveys of the Universe with tens of thousands or hundreds of thousands of galaxies, studying what everything looked like on the largest scales, finding new objects and galaxies that no-one had ever gazed upon before. So I was more than just intrigued when I saw the job advertisement for a postdoctoral research assistant at the Laboratoire d’Astrophysique Spatiale (LAS), in Marseille. “Observational cosmology / VLT-VIRMOS deep redshift survey” it said. They were looking for someone to help out with a survey of the distant Unvierse that would be an order of magnitude larger than anything attempted before using a new instrument on one of the four European Very Large Telescopes, in Chile. And I although in my ignorance I had never heard of the LAS, I had certainly heard of the person offering the position — Olivier Le Fevre. He had already authored or co-authored many papers on distant galaxies, surveys, clustering, all the kinds of topics that I had been immersed in during my studies. In my anglocentric innocence I wasn’t sure if this science was being done in the Old World. It seemed like a wonderful opportunity to do some exciting work on the shores of the Meditteranean. I had never been to the south of France before and after long years in the North of England I was ready for sunshine. I applied, and was invited for an interview.

I remember very clearly that I had arrived early at the LAS and was waiting in the lobby for Olivier to arrive. The building dated from the 1970s; outside the facade was all lightly-tarnished metal and glass and inside there were narrow corridors with worn linoleum on the floor. It had been well lived in. Outside, the sun shone brightly even on that early in the morning in winter and from the lobby it was hard to see who was coming through the doors. I stood with Vincent Le Brun, waiting, and I saw the silhouette of a tall man walking towards me, ah there he is now … and I was surprised. He seemed to be only slighly older than me. He was tall, handsome, athletic and impeccably dressed. But from his impressive publication record I was expecting a greybeard and not this man I saw before me.

During my one-day stay at the LAS I was very well looked after. Olivier and Alain Mazure took me to lunch at a restaurant nearby surrounded by the rolling green fields of a golf course. I remembered Roger Davies’ advice and spoke slowly during my talk which detailed our painful efforts during my thesis in Durham to map a tiny part of the sky with hundreds of hours of telescope time. I soon learned that Olivier’s under-construction VIMOS instrument, combined with the new wide-field cameras coming online at the Canada-France-Hawaii-Telescope, planned to make all this instantly redundant and open up a completely new window on the Universe. Precise distance measurements would be possible for tens of thousands of galaxies and there would be photometry for millions more. The galaxy-counting skills I learned at Durham were what the team needed to help make the input catalogues for this new instrument. After my talk, I spent some time with Olivier in his office. I was immediately taken by the his motivation and the vast amount of data he intended to collect and the chance that it might answer all those hanging questions we’d had until now. It was very exciting and it was in France!

A few months later I had finished my thesis, and on the first week in January 1999, I started my postdoctoral position at the LAS with Olivier. Incredibly, they had offered me the position; I was certain that there must have been crowds of people banging on the doors of the LAS. Only later did I discover that there was only one other applicant. “Observational cosmology”, as Olivier’s job application promised, had yet to really come to the LAS which was not yet on the post-doc radar. A colleague from the UK even confided in me that he wouldn’t ring a telephone number in a French laboratory in case the person picking up the telephone spoke French to him! I soon discovered I was the only post-doc in the lab and in those early days almost the only person in the building after 19:00. The LAS had a certain charm: and there was a long table outside under the trees where you could eat lunch most days. After a few months there I got to know some wonderful people and my French steadily improved. However, the “observational cosmology group” promised in Olivier’s job announcement for the moment didn’t comprise more than five people, including myself and two or three students. I mention all this here only to insist that the LAM (the fusion of the LAS and Marseille Observatory) has become the great force that is today in surveys largely thanks to Olivier’s work.

In 1999, however, such a happy ending was far from certain. Data was steadily arriving from CFHT telescopes in Hawaii and the computer in my office had attached disks piling up to the ceiling. Could we keep with the data? Worse yet, VIMOS turned out to be a very challenging instrument to build and commission. It took all of Oliver’s skills in management and persuasion to get the instrument on the sky and keep to the schedule. The team worked very well together and although there was a very long period before the spectra arrived Olivier kept us motivated. At an observing run in Hawaii I met Yannick Mellier who put the resources of TERAPIX at our disposal which helped us a lot with the early data. In the end, despite these difficult early years, tens of thousands of spectra were collected and VIMOS has gone on to be one the most successful instruments at ESO.

Already, in the first few years of new century, the context was changing: in the space of a few short years observational cosmology was gaining in importance in the community. The group at LAS was growing. The skills I had learned were becoming increasingly important, important enough that in the summer of 2003 I was recruited as a staff astronomer at the Institute d’Astrophysique de Paris. Olivier played a very important role in that change through his tireless support of countless other projects and instruments. For example, the VIMOS spectrograph turned out to be a crucial instrument for spectroscopic follow-up of the COSMOS survey, one of the largest-ever allocations of Hubble Space Telescope time. As well as that, Olivier brought TERAPIX into the COSMOS project to help with initial imaging at CFHT. That was the origin of my own highly fulfilling involvement with the COSMOS project, a collaboration which is still going strong after a decade.

In the winter of 2017 at a meeting in Paris I told him that I had been diagnosed with thyroid cancer. The treatment was going well, I said. I am sure I told him (as I told everyone) that if you want to have a cancer, that’s the one you should get; treatment is straightforward. Unfortunately, only a week or so later, he would fall from his bicycle and be diagnosed with a brain tumor. It didn’t slow him down. He worked as tirelessly as ever to realise his countless projects even as his body weakened. He still came to meetings. He was there at at our COSMOS meeting in Copenhagen in the summer of 2018. One evening, Olivier, and Olivier Ilbert and myself ate together in a restaurant, outside on the terrace. Olivier was unfailingly positive even though he must have known his chances of survival were slim.

Today, more than twenty years after my first meeting with him in that distant winter of 1998, observational cosmology and survey astronomy is now firmly established in France. And this is in large part due to Olivier’s work.