Universe Today
An international team led by researchers from Leiden University has produced the deepest and most detailed view of low-frequency radio galaxies in the Universe. Using the LOw Frequency ARray (LOFAR), the team observed ELAIS-N1 (European Large-Area ISO Survey-North 1), a region of the northern sky that contains very little galactic dust, gas, or stars. This makes the field highly favorable for deep multi-wavelength studies that probe the distant Universe.
For years, astronomers at the LOFAR observatory have been observing ELAIS-N1 to map low-frequency radio sources. The latest image has twenty times the resolution of the previous LOFAR image, which was made possible through advances in modern interferometry - a technique where light from multiple telescopes is combined to produce a single clearer image. The full image features 63,000 radio sources, including quasars and star-forming galaxies.
This new view of the low-frequency radio sky comes from 200 hours of observation and amounts to 400 terabytes of data in an 8-billion-pixel image. A few years ago, processing this amount of data from radio telescopes at such high resolution was impossible. But thanks to the Spider data-processing platform developed by researchers from the Netherlands Institute for Radio Astronomy (ASTRON) and their collaborators, and other improvements in calibration and data-reduction methods, processing times have been reduced by a factor of ten.
The core of the LOFAR radio telescope array near Exloo, Netherlands. Credit: LOFAR/ASTRON
"The entire dataset could be processed on Spider, the high-performance data processing platform hosted at SURF in the Netherlands, in just a few months," said Jurjen de Jong, a postdoctoral researcher at Leiden Observatory and ASTRON (who led the research). LOFAR's high sensitivity also revealed numerous filaments surrounding the radio galaxies, especially near galaxy clusters, as well as their morphology and spectral characteristics. Resolving these structures required combining high-resolution and low-frequency observations made possible by LOFAR.
Active Galactic Nuclei (AGN), also known as quasars, are particularly dominant in the image - the bright centers of galaxies powered by supermassive black holes (SMBHs) and their accretion disks. AGNs are also known to produce relativistic jets of superheated gas and dust that emanate from the black holes' polar regions and emit considerable radiation themselves. These structures are something LOFAR is especially well suited to observe, given its sensitivity to extended low-frequency radio emissions.
In previous, lower-resolution surveys, these distant galaxies and their relativistic jets would appear as little more than featureless blobs, making it difficult to distinguish individual galaxies from clusters. The high-resolution LOFAR data, in contrast, allow scientists to discern individual radio sources and massive jets, which can be traced in detail. This new view of the cosmos provides scientists with new opportunities to study how these jets interact with their environment and evolve over cosmic time.
The other major population in the image is the small, young galaxies that are still experiencing high rates of star formation. Because radio waves can pass through gas and dust that obscure the visible and infrared light of star formation, radio observatories provide a clear view of the processes taking place within these galaxies. This allows astronomers to study how galaxies that existed in the early Universe evolved into the older, larger spiral and elliptical galaxies we see in the local Universe.
The giant LOFAR radio telescope took this picture of the black holes at the heart of the active galaxy Cygnus A. Credit: J. McKean and M. Wise/ASTRON
According to the research team, this work demonstrates the potential of the upgraded LOFAR2.0 telescope, which ASTRON is currently working on with its European partners. The upgrades will enable wider, higher-resolution images, allowing LOFAR to remain competitive with next-generation radio telescopes like the Square Kilometer Array (SKA), which will combine the MeerKAT array in South Africa and the Inyarrimanha Ilgari Bundara (Murchison Radio-astronomy Observatory) in Australia.
The data will be especially useful when combined with images of the same patch of sky taken by other telescopes at other wavelengths. This includes optical, infrared, and X-ray observations, from which astronomers can determine properties like the distance and mass of each radio source.
Further Reading: Astronomie
