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Posts Tagged ‘Dark Energy Survey’

The largest map of dark matter made with direct measurements, unveiled today by two teams of physicists at the U.S. Department of Energy’s Fermilab and Lawrence Berkeley National Laboratory (Berkeley Lab) removes a key hurdle for tracing the history of dark energy in the universe using ground-based telescopes.

This work done by members of the Sloan Digital Sky Survey collaboration points to greater successes for upcoming sky surveys, including the Dark Energy Survey, which will turn on the Dark Energy Camera on the Blanco Telescope later this year, and then the Large Synoptic Survey Telescope and the HyperSuprimeCam survey.

To find and map the invisible dark energy and dark matter that make up about 96 percent of the universe, physicists look at their effects on the matter and radiation we can see, namely galaxies.

Surveying galaxies from Earth-based telescopes is cheaper than satellite-based experiments but had traditionally had the drawback of having to make due with a less clear view of the sky. The same atmospheric distortions that make stars twinkle blurs attempts to track invisible dark matter in the universe made by measuring the distortion of background galaxy shapes, a process called weak lensing. DES and LSST will use this technique to create the largest galaxy surveys ever, covering more than one-eighth of the sky.

Layering photos of one area of sky taken at various time periods, a process called coaddition, can increase the sensitivity of the images six fold by removing errors and enhancing faint light signals. The image on the left show a single picture of galaxies from the SDSS Stripe 82 area of sky. The image on the right shows the same area with the layered effect, increasing the number of visible, distant galaxies. Credit: SDSS.

Layering photos of one area of sky taken at various time periods, a process called coaddition, can increase the sensitivity of the images six fold by removing errors and enhancing faint light signals. The image on the left show a single picture of galaxies from the SDSS Stripe 82 area of sky. The image on the right shows the same area with the layered effect, increasing the number of visible, distant galaxies. Credit: SDSS.Particle physicists and astronomers from Fermilab and Berkeley Lab have demonstrated a new technique for weak lensing that lessens the blurriness and allows researchers to see fainter galaxies, providing a younger picture of the universe. The two teams essentially layered snap shots of these distorted galaxies, in a process called coaddition, to remove errors caused by equipment or atmospheric effects and to enhance very faint light signals coming from deep in the universe.

Both teams depended upon extensive databases of cosmic images collected by the Sloan Digital Sky Survey, SDSS, which were compiled in large part with the help of Berkeley Lab and Fermilab.

“These results are very encouraging for future large sky surveys. The images produced lead to a picture of the galaxies in the universe that is about six times fainter, or further back in time, than is available from single images,” says Huan Lin, a Fermilab physicist and member of SDSS and DES.

Surveys of galaxies across large swaths of the sky track how clumps of dark matter have changed over time as dark energy exerts its repulsive push on them. Clumps of dark matter not only distort the images of galaxies behind them, but they determine how galaxies cluster around them. By combining this information with redshift data, the observed change in the color of light emitted by a star or other celestial object that is moving away from Earth, it’s possible to trace how the distribution of matter in the universe has evolved over time, offering insight into the growth of dark energy.

Researchers hope this new tool will help answer one of the largest questions for upcoming dark energy surveys and in cosmology: whether dark energy is what Einstein called a “cosmological constant”, a counterbalance to gravity’s pull on matter? Or is it something else such as gravity behaving differently at cosmic scales. The variation or lack of separation between clusters of galaxies and within the clusters across time will lead to new insight into this question.

To build one of the largest maps of dark matter and track its evolution across eras, the teams looked at two manifestations of gravitational lensing: those caused by large galaxy clusters and those caused by the overall distortion spread across the large scale structure of the universe. This second effect is called cosmic shear. Both of these distortions are caused by the gravitational fields of clumps of dark matter acting as lenses, bending the light from galaxies behind them. This distorts the shapes of these distant galaxies, making them look more elliptical. By measuring the ellipticities, or amount of distortion, physicists can infer properties of the dark matter, such as its abundance and how clumpy it is and the masses of the clusters.

“This image correction process should prove a valuable tool for the next generation of weak-lensing surveys,” Lin says.

— Tona Kunz


Fermilab planning a busy 2012

Tuesday, January 3rd, 2012

This column by Fermilab Director Pier Oddone first appeared in Fermilab Today Jan. 3 .

We have a mountain of exciting work coming our way!

In accelerator operations, we need to give enough neutrinos to MINERvA to complete their low-energy run, enough anti-neutrinos to MiniBooNE to complete their run and enough neutrinos to MINOS to enable their independent neutrino velocity measurement that will follow up on last year’s OPERA results. We need to provide test beams to several technology development projects and overcome setbacks due to an aging infrastructure to deliver beam to the SeaQuest nuclear physics experiment. And we need to do all of this in the first few months of the year before a year-long shutdown starts. During the shutdown, we will modify the accelerator complex for the NOvA era and begin the campaign to double the number of protons from the Booster to deliver simultaneous beams to various experiments.

In parallel with accelerator modifications, we will push forward on many new experiments. The NOvA detector is in full construction mode, and we face challenges in the very large number of detector elements and large mechanical systems. Any project of this scale requires a huge effort to achieve the full promise of its design. We have the resources in our FY2012 budget to make a lot of progress toward MicroBooNE, Mu2e and LBNE. We will continue to work with DOE to advance Muon g-2. All these experiments are at an important stage in their development and need to be firmly established this year.

At the Cosmic Frontier, we will commission and start operation of the Dark Energy Survey at the Blanco Telescope in Chile, where the camera has arrived and is being tested. In the dark matter arena we will commission and operate the 60 kg COUPP detector at Canada’s SNOLAB and continue the run of the CDMS 15 kg detector in the Soudan Mine while carrying out R&D on future projects. We continue to have a major role in the operation of the Pierre Auger cosmic-ray observatory. In addition we should complete the first phase of the Fermilab Holometer, which will study the properties of space-time at the Planck scale.

At the Energy Frontier, we play a major role in the LHC detector operations and analysis. It should be a fabulously exciting year at the LHC as we push on the hints that we already see in the data.

Beyond construction and operation of facilities we continue our R&D efforts on the superconducting RF technology necessary for Project X and other future accelerators. We will be building the Illinois Accelerator Research Center and moving forward to connect our advanced accelerator program with industry and universities. Our rich program on theory, computation and detector technology will continue to support our laboratory and the particle physics community.

If we accomplish all that is ahead of us for 2012, it will be a year to remember and celebrate when we hit New Year’s Day 2013!


A four-ton digital camera landed safely in Chile last week on its way to making history by enabling the world’s largest galaxy survey, starting next year. Getting the camera there was a worldwide feat of technlogy and transportation prowess.

Doing big science, such as building the Dark Energy Camera, takes big effort and big cooperation. Building and installing one of the world’s largest digital cameras to conduct the most extensive galaxy survey to date as part of the Dark Energy Survey experiment required scientists and manufacturers from across the globe. Researchers from more than 26 institutions enlisted the help of 129 companies in the United States and about half a dozen in foreign countries to fabricate the often one-of-a-kind components for the camera.

Most components for the camera migrated to the Department of Energy’s Fermilab for testing and assembly, as seen in this timelapse video , before being shipped to the four-meter Blanco telescope in the remote Chilean mountains. The journey required help from planes, trains, trucks and boats to traverse continents and oceans, and ended with an 11-hour drive to a mountaintop.

The DES’s combination of survey area and depth will far surpass what has come before and provide researchers for the first time with four search techniques in one powerful instrument. To find clues to the characteristics of dark energy and why the expansion of the universe is accelerating, DES will trace the history of the expanding universe roughly three-quarters of the way back to the time of the big bang.
During five years of operation, starting in 2012, the 570-megapixel camera will create in-depth color images of one-eighth of the sky, or 5000 square degrees, to measure 100,000 galaxy clusters, 4,000 supernovae, and an estimated 300 million distant galaxies, about 10 million times fainter than the dimmest star you can see from Earth with the naked eye. It will yield the largest 3-D map of the cosmic web of large-scale structures in the universe.

–Tona Kunz


DES first-light countdown, 6 months to go

Blanco telescope, on left, at sunset in Chile. Photo: Brenna Flaugher.

I have promised to provide updates on our progress towards the first light of the Dark Energy Survey’s, or DES.  First light is the first official look at the sky after readying the camera and its detection software. If you recall, we were supposed to deliver the Dark Energy Camera, or DECam, imager this summer.

So, without further ado, I am pleased to announce: Here it is!

I have been collecting DES-related pictures and videos for a while and the picture to right by Fermilab photographer Reidar Hahn is by far my favorite shot of the imager (first published in Fermilab Today). It shows the focal plane completely populated with 74 shiny, blue CCDs, ready to catch some extragalactic photons.

Shipment arrangements and installation schedule are being worked out as I write. Our team has already set foot in Chile to assemble at the Blanco Telescope the various parts that we tested on our Fermilab telescope simulator in February. Installation will start soon.

I am joining them in November in Chile and can hardly wait. But this is when my wave-like abilities, which I mentioned in a previous post, comes to play. My wave function is now quite stretched as I perform a variety of tasks these days. Read on and see it for yourself.

Blue-tinged Charged Coupler Devices in the Dark Energy Camera imager. Photo: Reidar Hahn

Galaxy clusters are my favorite thing in the universe, and in addition to my work on the DES cluster analysis group I am now building a new catalog based on the Sloan Digital Sky Survey, or SDSS, data. Our group at Fermilab is wrapping up all the parallel threads of work on that data set, and that means that I am doing a lot of writing these days, too. Papers are coming out soon and this is terrific news, which puts my mind at ease with respect to that nightmarish pressure for publications.

I’ve also been volunteered to help in the calibration group by writing a code, which was being referred to as “George” until we found a more appropriate name. But since people now ask me, “How is George doing?” all the time, I am afraid the name has stuck. Right now I am working in the first module, “George I”, to process a series of monochromatic calibration images and create a map of the system response curve at every point of the DECam focal plane. This new task is exciting because it connects the instrument I helped build with the science I want to do (good calibration is an essential requirement for cluster science) and it also gives me the opportunity to learn more about our data management system.

The reason for my excitement about this is the fact that a reliable, fast and easy-to-use database is the key for success and productivity in our field. I use the SDSS SkyServer for all my SDSS analyses and it is just great to be able to upload a text file with sky coordinates and visualize, with a single click, all the objects you are interested in. Every time I submit a query to the SDSS database, using the CasJobs web interface or my own little scripts, I wonder what the DES equivalents for that will look like. It feels a little like waiting for the next release of your favorite gadget. And as a heavy user and big fan, I, of course, have my own wish list of improvements.

Blanco Telescope April 2011. Photo: Jose Francisco Salgado

My number one wish? Support to upload my own little codes, in addition to data tables, and run them directly on the query outputs. This way I could save only the processed tables, use them later in combination with other data, make all my plots and download only the final results. That would make my work so much easier!

Well, but I’d better stop here and go back to work. George is doing well today, but there is still a long way to go. I will be back with more updates soon. Stay tuned.

–Marcelle Soares-Santos


The last time I wrote a post was in February, ages ago in this fast-paced world. Since then, a lot of things have happened. I just flew back from the April Meeting of the American Physical Society in California, where I presented our most recent result from the Sloan Digital Sky Survey-III: the creation of the largest-ever 3D map of the distant universe. Thanks to the power sockets kindly provided by United on this particular flight, I can actually spend my time doing something useful while in this metal tube — attempt to write a marginally interesting post.

Anyway, my recent results were about the Lyman-alpha forest, a completely new technique that my colleagues and I got to work for the first time. It means a lot to me, mostly because there was a great deal of skepticism in the community on whether this technique would ever work, and given that I spent the past two years in the trenches trying to make it happen, I’m very happy. You can read more about it here. Fun fact: the media attention surrounding this announcement caused my name to appear on Fox News, a somewhat bizarre occurence for a European-style liberal like me.

What I want to tell you more about today is dark energy, which is a problem that is relevant both for my Lyman-alpha work as well as the Large Synoptic Survey Telescope (LSST) science that I discussed in this post. To put it mildly: dark energy is one big embarassement for modern physics. So, what is it?

A rendering of the Large Synoptic Survey Telescope, a proposed 8.4-meter ground-based telescope that will survey the entire visible sky deeply in multiple colors every week from a mountaintop in Chile. (Image credit: LSST Corporation/NOAO)

First, one important clarification: dark energy is not dark matter. Dark matter is a substance that is omnipresent in our universe and essentially behaves as a cold, invisible dust that collapses under its own gravity. The observational evidence for dark matter is overwhelming, but there are also many good theoretical ideas about what dark matter might be. Physicists have embarked on a long program to establish a “theory of everything,” or at least a “theory of many things.” We have unified electrodynamics and the weak interactions of particles — and the strong force can be self-consistently added — but how we combine these three forces with gravity is still an unsolved problem. There are many proposals on how to do it: supersymmetry, string theories, quantum loop gravity, etc.  The beauty of all these proposals is that that, in addition to having observational signatures at the Large Hadron Collider (LHC), they naturally explain dark matter. Most of these theories have at least one stable, weakly-interacting particle that could act as dark matter. The picture hasn’t quite clicked together yet, but this will indeed happen in the next couple of years, as more results come from the LHC.

Dark energy, on the other hand, doesn’t have such beautiful connections to fundamental physics. Nobody has the slightest idea of what if could be and how it could fit into the bigger picture. So what do we know?

In the late 1990s, observations of the dimming of distant supernovae showed that the universe is undergoing a phase of accelerated expansion. In other words, the universe is expanding faster and faster. This is very counterintuitive: if you throw a ball upwards, it keeps slowing down until it reaches its maximum height and then it falls down. The universe does something similar: After the initial kick, which we call the Big Bang, the expansion of the universe went slower and slower. But, some 7 billion years ago, the universe started to accelerate. It’s like throwing a ball in the air and watching it do what it’s supposed to do for a while before it suddenly changes its mind and zooms off to the skies!

A simulated 15-second LSST exposure from one of the charge-coupled devices in the focal plane. (Image Credit: LSST simulations team)

After the initial discovery of dark energy through distant supernovae, the evidence grew stronger and stronger and now we see it in many different measurements of the universe: the Lyman-alpha forest measurements that I mentioned earlier, as well as measurements from the Dark Energy Survey and LSST will all constrain the behavior of dark energy. The amazing thing is that we can describe this accelerated expansion of the universe by putting an extra term in the equations that describes the evolution of the universe — the so-called cosmological constant. At the moment, all observations are consistent with adding this one simple number to our equations. But this number has nothing to do with the physics that we know; it is of a wrong order of magnitude and shouldn’t be there to start with. So we all measure like wackos and hope that we will detect some small deviation away from this simple solution. This would indicate that dark energy is more complicated, somewhat dynamical, and thus, give us a handle on understanding it. But it might turn out that it is just that — a cosmological constant with no connection to anything else. In the latter case we are stuck for the foreseable future hoping that someone will eventually be lucky enough to make an observation or theoretical insight that will bring everything together.



DES First Light Countdown, seven months to go

At the time of my first post in the countdown to first light series, some people suggested that I write more on what I really do and what it is like to be a postdoc in the Dark Energy Survey, DES. And as much as I feel hesitant to turn the spotlight to myself, I would hate to let my very first readers down. So read along and you will learn, from a very particular perspective, how much progress we have made in the last two months.

DECam focal plane at Fermilab almost full of CCDs. Credit: Marcelle Soares-Santos

 Being a postdoc is like being a photon. You have a wave function and, while your career momentum may be well determined, your location in the multiverse of projects, working groups, meetings and responsibilities is very uncertain.

 During the Dark Energy Camera, DECam, test phase on the telescope simulator my wave function nearly collapsed around the Fermilab Silicon Facility, or SiDet. I was sitting right next to the camera, testing the ever evolving data acquisition system and the new components (shutter, filter changer, hexapod…) as they came online. This phase was completed in February and since then my wave-like behavior is more evident again. We have changed gears towards filling the focal plane with our brand new CCDs and preparing the camera for shipment to the Blanco telescope at Cerro Tololo Inter-American Observatory, or CTIO, in Chile. This week I am in Chile, attending the DECam integration meeting. It is my first time at the observatory and not only I am having a great time, but I am also learning a lot!      

Cerro Tololo Inter-American Observatory in Chile. Credit: NOAO

But being a photon also means that your rest mass is zero and your wave length is inversely proportional to the energy you dedicate to each particular task. Supervisors and project managers seem to know this very well and deliberately loosen or tighten their grip as they see fit. But it actually depends on the time scale of each project. The fact is that from time to time you feel the stress decrease in one area and your wave function automatically stretches to other activities.

DES simulated image. Credit: DES collaboration

I am also working on the cluster finders comparison project, which will help DES identify, with high efficiency, a sample of more than 100,000 galaxy clusters, the largest gravitationally bound objects in the universe. This area is where most of my science interest lies. I developed

a galaxy cluster finder and tested it on DES simulations, computed the selection functions to be applied to our data and studied the systematics. That meant time in front of a computer terminal, programming instead of testing camera components. I find programming a lot more fun and I like the flexibility to work from virtually anywhere. My office (well, it is a cube really) is the natural choice, but I do a lot of this work at home too (yes, work-life balance is that concept from the seventies that I haven’t internalized yet).

Last week we finished the installation of the software framework for the cluster finders comparison project — we have a handful of cluster finding algorithms in our collaboration.  This fall we will conduct a comprehensive test of our pipeline, through what is called the Blind Cosmology Challenge. The idea is to verify that we can recover the right answer in a simulated data set. This would prove our ability to measure the dark energy parameters DES wants to study. A great overview of this challenging project was presented by one of our collaborators in a talk at the KITP Conference last month.

So here is where we stand, at the seven-month mark. Integration and commissioning phases are imminent. And we are working hard to get ready on several fronts simultaneously. This requires a very broad wave function!

— Marcelle Soares-Santos




A replica ring of the top-end of the Blanco telescope built at Fermilab to test assembly and operation of the dark energy camera before shipment to Chile. Credit: Fermilab/Cindy Arnold

This article ran in DOE Pulse April 4.

Building and installing one of the world’s largest digital cameras to solve the mystery of dark energy requires the collaboration of scientists and industry from across the globe. The Dark Energy Survey’s combination of survey area and depth will far surpass the scope of previous projects and provide researchers for the first time with four search techniques in one powerful instrument. More than 120 scientists are collaborating to determine the true nature of dark energy, the mysterious force that accelerates the expansion of the universe. Taking images of galaxies from the time the universe was only a few billion years old, the DES will trace the history of the expanding universe roughly three-quarters of the way back to the time of the Big Bang.

But first researchers needed to build the 570-megapixel camera at DOE’s Fermi National Accelerator Laboratory and make sure it works. Nearly all of the camera’s parts made their way to Fermilab for assembly and testing during the last 12 months. The components were assembled and operated on a full-size replica of the front end of the 4-meter Blanco telescope in Chile, built by Fermilab and Argonne National Laboratory.  Testing finished successfully in February. During the next few months, physicists will be putting the finishing touches on pieces of the camera and shipping them to the Cerro Tololo Inter-American Observatory in Chile where they will receive another round of tests before installation.

The high-tech supply chain tapped the expertise at four DOE Office of Science national laboratories and more than two dozen institutions and universities in the United States and abroad.  More than 120 companies in the United States contributed know-how and parts. Fermilab took the lead in the assembly and testing of the camera and building a cryogenics system several times larger than those used in previous ground-based sky surveys, while Berkeley and Argonne national laboratories played key roles in the camera development.

Berkeley Lab developed the Charge Coupled Devices used in the camera and did some of the processing of the silicon for the CCDs before sending the pieces to Fermilab for packaging of CCD chips. The unique design of these CCDs will give the camera unprecedented sensitivity for red and near-infrared wavelengths, allowing it to record more light for a given exposure time. The camera contains 62 CCDs for observing with 8 million pixels each, plus 12 CCDs with 4 million pixels each for guiding and focusing.

Argonne National Laboratory helped construct the calibration camera to conduct a mini-sky survey last year from a telescope adjacent to the Blanco telescope. This scaled-down version of the dark energy camera allowed for testing of the experiment hardware, software and observing strategies as well as created a baseline of celestial objects for Dark Energy Survey. Argonne also constructed several smaller components for the full-size camera and some large mechanical systems, including the heavy apparatus that installs and removes a 1-ton mirror from the front of the camera.

SLAC National Accelerator Laboratory took the lead in constructing a separate, small telescope with an infrared camera that will sit on a mountain near the Blanco telescope in a separate enclosure. This telescope will monitor cloud coverage so that the Dark Energy Camera can adapt its survey modes to various atmospheric conditions.

The DES collaboration expects to take its first astronomical images with the installed Dark Energy Camera before the end of 2011.

— Tona Kunz


As the time for our camera’s first light approaches, workload and excitement increase exponentially among the Dark Energy Survey collaborators and it is about time we start sharing the latter. Beginning today, you will find here at Quantum Diaries an insider’s account of our fast progress, frequently updated as we countdown to first light.

So, here we go. If you haven’t heard of us yet, DES is an experiment designed to investigate dark energy, one of the most trending topics of the last 30 years, featured among the top priorities in the world-wide scientific agenda despite a recent funding blow up. DES will image an area of 5,000-square degrees (nearly 1/8 of the sky) using five optical-bands, obtaining detailed measurements of about 300 million galaxies. With this data we can shed light on the mystery of cosmic acceleration by analyzing four complementary probes: supernovae, baryonic acoustic oscillations, galaxy clusters and weak lensing.

DES will use its own powerful new instrument, the Dark Energy Camera, or DECam, which is under construction at  Fermilab.  Building an entirely new system to answer a specific question is a growing trend in astrophysics, probably a consequence of developing close ties with the field of high energy physics.

This 570-megapixel, giant camera is being tested on a telescope simulator (the yellow and red rings that you see in the video) until the end of this month. As a Fermilab postdoc, I am heavily involved in these tests, together with a team that keeps up the fast pace even during the blizzard last week.

Check out this time-lapse video of the DECam construction:

We are now getting ready for a simulated observing run, a comprehensive integration test of the full system. We will use a star projector to simulate the sky and the goal is to take one night’s worth of data. The atmosphere here at the lab is of stress and excitement as this is our last test of the full system before we bring DECam down from the telescope simulator. The results of this test will be very important to guiding us through the next steps.

So here is where we stand nine months before first light. Stay tuned for more updates here or follow us on Facebook. Leave a message in the comments if you want to know more or would like to visit us while the camera is still up on the simulator.

–Marcelle Soares-Santos