The European radiotelescope LOFAR, has obtained images of quasars in the reionisation era, only 400-800 mio years after Big Bang

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.

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.

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 arcseconds 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.

This is an important record for the time being for the LOFAR radio-telescope array. 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 were presented at an international conference in Zadar, Croatia, last week and were eagerly awaited by the astronomical community.

Source: Netherlands Institute for Radio Astronomy