LOFAR on the Map of GPU Computing.

Of possible interest to those involved in LOFAR is this map of the GPU (Graphical Processing Unit) computing usage for research. The LOFAR Epoch of Reionization Key Science project makes it onto the map in Groningen where GPUs are being used for signal and image processing of the data generated by LOFAR for this experiment.  

LOFAR Makes Deeper Images of the Universe than ever before

The below press release was posted at ASTRON today describing some very deep images taken by LOFAR as part of the commissioning for the Epoch of Reionization project (the part of LOFAR which is trying to look for evidence of the first stars turning on).

See the press release on the ASTRON website (copied below).

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LOFAR makes deeper images of Universe than ever before

An international team led by astronomers at ASTRON and the Kapteyn Institute of the University of Groningen have used the LOFAR telescope, designed and constructed by ASTRON, to make the deepest wide-field images of the sky in the relatively unexplored part of the spectrum around 150 MHz. It reveals faint radio sources never seen before.

3C196-Sarod: A tiny part of the LOFAR image of the field centered 

on the North Celestial Pole. It shows at least 7 discrete sources, some 

of them double or complex. The faintest source has a flux density of only

 a few mJy at 150 MHz.  The image has an angular resolution of 8 arcseconds 

but still needs to be deconvolved. The data was processed by Dr. Sarod Yatawatta 

on the EoR-cluster at the University of Groningen

The results were presented at an international conference in Zadar, Croatia, last week (May 23-27, see http://www.astron.nl/FGC2011) and were eagerly awaited by the astronomical community. The Zadar conference (organised by team member dr. V. Jelic, ASTRON), discussed the properties of the foregrounds that trouble our view of the distant Universe. Two projects were central at the conference: Planck observations of the Cosmic Microwave Background and (searches for) redshifted 21cm line observations of an era known as the Epoch of Reionization (EoR). This phase in the Universe is believed to have taken place in the period between about 400 and 800 million years after the Big Bang. The birth of the Universe took place about 13.8 billion years ago. During the EoR the neutral hydrogen was slowly disappearing, probably as a result of the strong 'ionizing' power of the first stars and quasars. Detecting the EoR is one of the hottest projects in astronomy today.

A group of astronomers based at ASTRON and the Kapteyn Institute of the University of Groningen, headed by Prof. Ger de Bruyn, Dr. Michiel Brentjens, Prof. Leon Koopmans and Prof. Saleem Zaroubi, is in the race to first detect these signals. They lead a team of about a dozen members, including astronomers currently working in Germany, USA, Canada and Sweden (see http:/www.astro.rug.nl/~LofarEoR). The results presented at the conference constitute an important step on the road to detecting the elusive signals. However, there is still a long way to go along this road.

Most of the antenna stations of the International LOFAR Telescope have already been rolled out across the Netherlands and Europe. It has been taking data for a large number of astronomers after its official opening by Her Majesty queen Beatrix of the Netherlands last year. The LOFAR data on which the images are based, were obtained in a 6-hour synthesis on the night of 29/30 January 2011 and the evening of 1 April 2011 using 18 core stations and 7 remote stations. Signals were recorded with the High Band Antennas and covered the frequency range from 115 - 163 MHz. After initial processing on the central LOFAR cluster they were transferred and further processed on a cluster dedicated to the processing of data for the LOFAR Epoch-of-Reionization project. This cluster is also located at the Computing Centre of the University of Groningen.

Cutouts from a very small part of the giant images are shown in the associated figures. One of the fields is centered at the celestial North Pole which is special in the sense that night-time observations can be obtained all year round. The second field was centered at the bright compact quasar 3C196 in the constellation of Lynx. The images, which have a resolution of 8" are already comparable to, or even slightly better, than the best published images taken with the Giant Meter Wavelength Radio telescope (GMRT) in India. The images contain a large number (>1000) of both very bright and very faint sources, spanning a so-called dynamic range of more than 200,000:1 in brightness between sources in the 3C196 image.

3C196-Panos: A very small part of the raw LOFAR image of the field centered 

on the bright quasar 3C196. It  shows tens of discrete sources, the faintest having 

a flux density of only a few mJy at 150 MHz. The image has an angular resolution 

of 8 arcseconds.  The image still needs to be deconvolved. The data was processed 

by Dr. Panos Labropoulos on the EoR-cluster at the University of Groningen.

This is an important record for the time being for LOFAR. The image quality, however, is still not perfect and significant improvements can be expected in the months ahead using improved knowledge of the effects of the LOFAR station beams. Continued efforts are also needed to improve the software to deal with imaging artefacts and the ionosphere. These two fields and several others will be observed for about 100 nights to conclusively detect signals from the EoR.

The results, and their implications, will soon be written up in two papers headed by Dr. Panos Labropoulos (ASTRON) and Dr. Sarod Yatawatta (ASTRON/ RuG) who lead the processing of the datasets for the 3C196 and NCP fields, respectively.


End of press release

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For more information, please contact:

ASTRON:

Prof. Ger de Bruyn, senior astronomer. Phone: +31 521 595 787. E-mail: ger@astron.nl

Dr. Michiel Brentjens, support scientist. Phone: +31 521 595 781. E-mail: brentjens@astron.nl

University of Groningen:

Prof. Leon Koopmans, astronomer. Phone: + 31 50 363 6519. E-mail: Koopmans@astro.rug.nl

Captions to the images:

3C196-Panos: A very small part of the raw LOFAR image of the field centered on the bright quasar 3C196. It  shows tens of discrete sources, the faintest having a flux density of only a few mJy at 150 MHz.The image has an angular resolution of 8 arcseconds.  The image still needs to be deconvolved. The data was processed by Dr. Panos Labropoulos on the EoR-cluster at the University of Groningen.

3C196-Sarod: A tiny part of the LOFAR image of the field centered on the North Celestial Pole. It shows at least 7 discrete sources, some of them double or complex. The faintest source has a flux density of only  a few mJy at 150 MHz.  The image has an angular resolution of 8 arcseconds but still needs to be deconvolved. The data was processed by Dr. Sarod Yatawatta on the EoR-cluster at the University of Groningen

Acknowledgements:

The data were obtained as part of the commissioning of LOFAR and the results obtained thus far are a tribute to the hard work of a large group of people, usually referred to as the LOFAR collaboration.  

About LOFAR:

The International LOFAR telescope is a Pan-European collaborative project led by ASTRON Netherlands Institute for Radio Astronomy. Combining thousands of simple dipole receivers with powerful digital signal processing and high-performance computing, LOFAR can rapidly survey wide areas of the sky, looking in multiple directions simultaneously and relatively unexplored low frequencies, opening open up a new window for astronomers.

LOFAR will focus on six areas of research:

1. The Epoch of Reionisation - understanding how the first stars and black holes made the universe hot.
2. Extragalactic surveys - what is the history of star formation and black hole growth over cosmological time?
3. Transients and Pulsars - probing the extreme astrophysical environments that lead to transient bright bursts in the radio sky.
4. Cosmic rays - what is the origin of the most energetic particles in the universe?
5. Solar and space environment - mapping the structure of the solar wind, how it relates to solar bursts, and how it interacts with the Earth.
6. Cosmic Magnetism - what is the origin of the large-scale magnetic fields that pervade the universe?

See also www.astron.nl and www.lofar.org.

LOFAR on the Jodcast

You can listen to me on the May 2011 Extra Jodcast talking about LOFAR (among other things). I'm the first interview in the podcast.

What might LOFAR see of the first stars?

One of the main science drivers for LOFAR is the detection of the point in the history of the Universe when the first stars turned on.

We know that the Universe formed in a Big Bang, after which it was filled a hot soup (plasma) of elementary particles (like electrons, protons, neutrons and photons as well as much more exotic things). When the Universe cooled sufficiently, the electrons combined with the protons to make hydrogen atoms. At that point the photons which had previously been stuck bumping around between the particles could finally stream across the universe - and we see from that time the first light in the Universe - now cooled to microwave radiation (what we call the cosmic microwave background, or CMB).

After the CMB not much happened for a long time. There still wasn't a lot of structure in the Universe - no stars or galaxies. There was nothing to create any light - so we call this period the "dark ages". During this time the material in the Universe ever so slowly collects together under its gravity. Eventually parts of the Universe start getting more and more dense, and the first stars turn on in the densest parts. Suddenly there is light in the Universe once more, and all these new photons hit the hydrogen atoms and strip them of their electrons (ionizing them, but since they started before the CMB as separate protons and electrons, we like to call it "reionization").

As I described in a previous blog post "LOFAR in Sky and Telescope", and you can read about in the May 2011 issue of Sky and Telescope, neutral hydrogen emits a characteristic spectral line at 21cm (1.4 GHz), due to hyperfine splitting of it's ground state. The neutral hydrogen that was around in the Universe just before the first stars turned on was emitting this line, which is now redshifted to much lower frequencies (which we think should be in the range that LOFAR can detect). Suddenly at the redshift which the first stars turned on, the amount of this 21cm emission will drop dramatically. It is this phase change in the Universe which LOFAR hopes to detect.

A slice through a simulation of the reionization of the Universe. Credit Illian Illiev, SEPnet/Sussex

Exactly when and how the first stars turn on in the Universe is an important measurement to further our understanding of cosmology. Researchers involved in LOFAR (and LOFAR-UK) are working on models of what LOFAR and other telescopes like it might see. One such researcher is SEPnet Fellow Dr. Illian Illiev at the University of Sussex. It was his images and animations of what reionization might look like which were used to illustrate the Sky and Telescope article.

Reionization Animation.

Here's a description of the image and animation provided by Illian:

This is what a giant radio telescope like LOFAR is expected to see as it looks deeper into the past (going right) - a sea of neutral hydrogen atoms (yellow) gently excited into emission by the cosmic microwave background photons.

As the very first stars and galaxies form in the universe, some of their radiation is energetic enough to kick out the electron out of the hydrogen atom (a process called ionization), which leads to the gas 'disappearing' from point of view of the radion telescope, illustrated by the blue regions above, growing with time (going left) as more stars form over time.

The variation in the intensity of the yellow across the image indicates regions with different density, the higher the density, the more intensive the colour (since there is higher concentration of emitting atoms there). This is a manifestation of the 'Cosmic Web' of structures - a honeycomb-like structure which forms due to gravity.

LOFAR in Sky and Telescope

One of the feature articles in the May 2011 edition of Sky & Telescope is "The End of the Cosmic Dark Ages" (or "Cosmic Enlightenment - the first stars") which covers how the International LOFAR Telescope plans to try to detect the "phase change" in the early universe when most of the hydrogen changes from neutral to ionized (called "reionization"). This is detectable by low frequency radio telescopes as a sudden decrease in (redshifted) 21cm emission. It works like this.... Neutral hydrogen emits a characteristic spectral line at 1.4 GHz (or 21cm) due to hyperfine splitting in its ground state. Ionized hydrogen does not emit this line. Because of the expansion of the universe, 21cm emission from very early in the universe has been redshifted to much longer wavelengths (detectable by LOFAR hopefully), and the amount of the redshift tells you how far back in the universe you're looking. LOFAR plans to look for a frequency at which redshifted 21cm emission suddenly stops being present (ie. the emission is there at longer wavelengths, but not at shorter ones).  This would provide a time stamp for when the phase change happened which is an important measurement to further our understand of the evolution of the universe.

Anyway check out the article to learn more. It features a series of images (and a link to an animation) from a simulation of the universe being reionized done by LOFAR-UK member Illian Illiev (the SEPnet LOFAR fellow at the University of Sussex) and quotes from LOFAR-UK member Steve Rawlings (from the University of Oxford).

It is a very nice article, and I'm very grateful to Sky and Telescope for sending me a preview version (we helped them locate some nice images of LOFAR stations). There are a couple of small corrections I would like to point out though. The first is that the image shown on Page 28 called "LOFAR First Light", described as being the first image taken by the whole array isn't quite that. That image is described in an earlier blog post "First Images from LOFAR Including Chilbolton" and was taken as part of observations which included the Dutch core and remote stations, as well as Chilbolton, Nancay and Tautenberg (but not the other German stations, or the Swedish one), and as I understand it that image actually only included data from the Dutch stations - it's the zoom in shown in our blog post which included data from the LOFAR-UK station). Also as we have discussed it's not the separation of the array, but the number of antennas and collecting area which make the International LOFAR Telescope the largest telescope in the world (at the moment). Finally Steve Rawlings is not leading LOFAR-UK (although he is very heavilly involved). Rob Fender (Southampton) is our current leader, soon to be replaced by Phil Best (Edinburgh).